NC0082376_Report_20071001

Assessment of Raleigh's Recycle System
Submitted to
City of Raleigh
Raleigh, North Carolina
Submitted by
EE&T, Inc.
712 Gum Rock Court
Newport News, Virginia 23606
October 2007

CONTENTS
LIST OF TABLES ....................................... ...
LISTOF FIGURES........................................................................................................................................ iv
EXECUTIVE SUMMARY........................................................................................................................... vi
OBJECTIVESAND APPROACH.............................................................................................................. 1
BACKGROUND............................................................................................................................................ 4
RecycleSystem.................................................................................................................................. 4
DataUsed in This Evaluation....................................................................................................... 7
SamplingLocations......................................................................................................................... 10
RESULTSOF DATA ANALYSIS...........................................................................................................
11
Flow....................................................................................................................................................
11
Turbidity.............................................................................................................................................
12
TotalOrganic Carbon.....................................................................................................................
18
Manganese........................................................................................................................................
20
Iron......................................................................................................................................................
22
TotalColiform..................................................................................................................................
23
HeterotrophicPlate Count.............................................................................................................
23
TotalSuspended Solids..................................................................................................................
24
TTHMand HAA5...........................................................................................................................
24
Cryptosporidiumand Giardia.......................................................................................................
25
SUMMARY................................................................................................................................................... 28
RECYCLE REQUIREMENTS...................................................................................... ........... 21
.................
RECOMMENDATIONS............................................................................................................................. 32
REFERENCES............................................................................................................................................... 36
ii

LIST OF TABLES
Measured Cryptosporidium and Giardia concentrations.............................................................. 26
2 General concentration trends for recycle, raw, and influent water ............................................... 28
iii

LIST OF FIGURES
1 Schematic of recycle/residuals system (as of June 2007).............................................................. 5
2 Flow rates (Mar 2006 — Feb 2007)................................................................................... 37
3 Recycle flow rate (Mar 2006 — Feb 2007)........................................................................ 38
4 Turbidity (Mar 2006 - Feb 2007)...................................................................................... 39
5 Turbidity: log -scale plot (Mar 2006 - Feb 2007).............................................................. 40
6 Raw lake water and recycle water turbidity (Mar 2006 - Feb 2007)................................ 41
7 Turbidity (May — Aug 2006)............................................................................................. 42
8 Settled and finished water turbidity (May — Aug 2006)................................................... 43
9 Turbidity during Nov. and Dec. 2006............................................................................... 44
10 Recycle, settled, and finished water turbidity (Mar 2006 — Feb 2007)............................. 45
11 TOC concentrations (Feb 2006 — Mar 2007).................................................................... 46
12 Percent TOC removal (Feb 2006 — Mar 2007)................................................................. 47
13 TOC concentrations (May — Aug 2006)........................................................................... 48
14 Settled water TOC concentrations (Jan — Mar 2007)........................................................ 49
15 Manganese concentrations (Mar 2006 - Feb 2007).......................................................... 50
16 Finished and raw lake water manganese concentrations (Mar 2006 - Feb 2007)............. 51
17 Influent manganese compared to applied dose and influent turbidity (Mar 2006 —
Feb2007).......................................................................................................................... 52
18 Manganese concentrations during the period of no permanganate addition (July 5 —
Nov12, 2006)........................................................................................................ ..... 53
19 Manganese concentrations (May — Aug 2006)................................................................. 54
20 Manganese concentrations for raw lake water and finished water (May — Aug 2006) .... 55
iv

21 Source of manganese over time (Mar 2006 - Feb 2007).................................................. 56
22 Manganese mass loadings for raw lake water vs. recycle water
(Mar 2006 - Feb 2007)...................................................................................................... 57
23 Manganese mass loadings during the period of no permanganate addition (July 5 —
Nov12, 2006)......................................... ::........................................................................ 58
24 Iron concentrations (Mar 2006 - Feb 2007)...................................................................... 59
25 Applied dose of ferric sulfate (Mar 2006 - Feb 2007) ........................... ............ 60
................
26 Finished water iron concentrations (Mar 2006 - Feb 2007)............................................. 61
27 Iron concentrations (May — Aug 2006)............................................................................. 62
28 Total coliform (Mar 2006 - Feb 2007).............................................................................. 63
29 Heterotrophic plate count (Mar — Sept 2006)................................................................... 64
30 Total suspended solids (Mar — Sept 2006)........................................................................ 65
31 Finished water TTHM and HAA5 (Mar 2006 - Feb 2007).............................................. 66
32 Finished water TTHM and HAA5 versus finished water TOC (Mar 2006 - Feb 2007) .. 67
33 Finished water TTHM and HAA5 versus influent water TOC (Mar 2006 - Feb 2007) ... 68
VA

EXECUTIVE SUMMARY
Objectives and Approach
An extensive evaluation of the E.M. Johnson water treatment plant's waste stream
recycling system and related water quality data was performed to determine if the recycling
practice has any observable adverse impact on finished water quality. Plant schematics and
existing data on the residuals system, recycle quality, reservoir quality, and plant operating data
were obtained and reviewed. These data were then compared to recommendations in the
AWWA report "Self Assessment of Recycle Practices" previously prepared by EE&T, Inc.
(Cornwell, et al., n.d.).
The evaluation process examined raw source (lake) water, recycle water, combined
influent, filtered water, settled water, and finished water quality over time. Water quality and
flow data were obtained primarily for a full one-year period, from March 1, 2006 through
February 28, 2007, and the following primary scenarios were considered to help determine if
recycling of the treated Spent Filter Backwash Water (SFBW) supernatant has had any adverse
impacts on treated water quality:
1. Comparison of water quality during periods with and without recycle
2. Normal vs. worst -case conditions:
High water production (high flow)
High influent turbidity
• High Temperature (for disinfection by-product (DBP) formation)
• Substantial change in operations (e.g., doubling of the ferric sulfate dose)
• Low water production (low total flow) with recycling
Each of these scenarios was examined for its potential impact on a series of different water
quality parameters, including turbidity, TOC, manganese, iron, total coliform, HPC, suspended
solids, THMs and HAAs, and protozoa (Cryptosporidium and Giardia).
vi

Summary of Results and Discussion
The recycle practice did not have any adverse impacts on finished water quality for any
of the water quality parameters examined. In fact, concentrations of several key parameters in
the recycle water were less than that of the raw water (e.g., turbidity, TOC, TSS), while in cases
where the recycle water did have a higher concentration than the raw water (e.g., Mn, Fe, BPC)
there was no observable impact at any time on finished water quality.
There are several positive aspects of the E.M. Johnson water treatment plant's recycling
system that help provide for no observable adverse impact from the recycling on finished water
quality. First, the physical system is well -designed and relatively extensive. Secondly, WTP
personnel appear to do an excellent job monitoring performance of the various residual and
recycle treatment units and responding to changes in water quality as needed. Lastly, in summer
2007 (subsequent to the period of the data analyzed in this report), three significant improvements
were made to the recycle system at the WTP, including (1) a UV disinfection treatment system
was installed for the backwash water settling basin supernatant to help reduce or eliminate the
viability of bacteria, Cryptosporidium, Giardia, and other pathogenic microorganisms; (2) a new
recycle pump station was constructed that now directs the backwash water settling basin
supernatant (after UV disinfection) to both the East and West raw water reservoirs; and (3) piping
and valve improvements were made to ensure all of the drying bed underdrain water is directed
to the sewer system, which should lower the manganese levels in the settling basin supernatant.
Recommendations
Based on the above analysis, it is apparent that the recycle system is well -designed and
well -operated. Nonetheless, certain improvements could be made to improve recycle water
quality, and additional study performed to further understand some of the key issues.
Accordingly, we offer the following recommendations:
1. Issue: When the main WTP sedimentation basins are cleaned out, the wash water
is currently routed to the SFBW clarifiers. This arrangement results in substantial
vii

fluctuations of recycle water turbidity levels and levels that are often higher than
the raw lake water turbidity. There would be much less impact from this wash
water if it was instead directed to the splitter box leading into the three thickeners.
That way the wash water would be treated with polymer and clarification prior to
that supernatant entering the SFBW clarifiers.
Recommendation: Install appropriate piping and valves to route the wash water
from the five main WTP sedimentation basins to the splitter box entering the
thickeners, and discontinue the current practice of routing that wash water directly
to the SFBW clarifiers. Draining of the clear water in the basins should still be
directed to the SFBW settling basins, and the wash water used for cleaning out the
solids could be directed to the thickeners. Currently finished water is used to
wash the main WTP sedimentation basins, and WTP staff are concerned that the
relatively high alkalinity in the finished water would affect the settling in the
thickeners if it was directed to them. Accordingly, if the wash water is directed to
the thickeners, the effect of using finished water on thickener settling should be
evaluated, and if there is an adverse impact then settled water should be used for
this washing (a means of storing and pumping the settled water may be
necessary). Further analysis of the potential ramifications of this recommendation
should be performed to assess all potential issues.
2. Issue: An improved mass balance analysis would be useful to better understand
the fate of manganese in the WTP. Also, manganese levels in the SFBW settling
basin supernatant (recycle water) were historically as high during periods when
permanganate was not used as they were when it was being applied, and it would
be good to determine the source of that manganese. Until piping improvements
were made in May 2007, some of the underdrain water from the filter cake drying
beds (which is high in manganese) was inadvertently pumped to the SFBW
settling basins. Permanganate has been used continuously since that time, so it is
as yet unknown if the piping improvements will help reduce recycle water
manganese levels.
viii

Recommendation: Measure the manganese concentration of the thickener
overflow and the SFBW (during both periods of permanganate use and non-use),
and perform a mass balance analysis. Also, when permanganate use is next
discontinued, increase the frequency of analysis of manganese in the SFBW
supernatant to daily to better assess any improvement in manganese levels
(currently weekly analyses are performed).
3. Issue: No TTHM of HAA5 data are available for the recycle water; only finished
water TTHM and HAA5 data are available. The highest DBP results of the year
were obtained during the warmest month (83.4 µg/L for TTHM and 66.7 µg/L for
HAA5 on August 7, 2006) Since these numbers are at least approaching the
future LRAA MCL, it would be good to determine if recycle is contributing to the
levels. Recycle can add to both the instantaneous DBP levels by recycling
preformed DBPs and add to the formation potential by adding precursors.
Recommendation: Obtain TTHM and HAA5 data for the recycle stream during
the warmest months (July and August, when DBP levels are expected to be
highest) at the same time as the monthly DBP sampling of the finished water.
Analyze for both instantaneous DBPs and SDS levels by adding additional
chlorine, buffering the pH to the distribution system level, and holding for an
appropriate time (— 3 days).
4. Issue: The City is currently required by the North Carolina Department of
Environment and Natural Resources (NCDENR) to discharge the SFBW settling
basin supernatant (recycle water) to a nearby unnamed tributary of Honeycutt
Creek for one 2-week period each year. The above analysis showed that this
requirement is unnecessary and unduly burdensome. In fact, many parameters are
lower in the recycle than the raw water and thus improve the plant intake levels.
The requirement puts. a physical and water quality load on the receiving stream
(normally dry except for storm events) with no recognizable benefit to the WTP,
ix

and can lead to unnecessary objections from local residents who are not familiar
with the specific quality of the discharged water nor the reasons for its discharge.
Recommendation: The City should negotiate with the State to rescind the
requirement for occasional discharge of SFBW settling basin supernatant to the
nearby creek. The NPDES permit that allows that discharge should be
maintained, however, in the event of some unforeseen circumstance where
operational conditions mandate a release of SFBW settling basin supernatant to
the creek.
5. Issue: The City has resisted using a polymer in the SFBW settling basins to
improve coagulation and clarification because of toxicity concerns from the
polymer for occasions when the supernatant is discharged to the nearby unnamed
tributary of Honeycutt Creek, as required for one 2-week period per year by the
NCDENR. The City previously determined in 2005 that the polymer used for the
splitter (entering the three thickeners) and the filter presses was causing toxicity in
the water discharged to the creek. Subsequent modifications to the residuals
system now direct the press filtrate to the sewer, and no polymer is recycled from
the presses. Any polymer left over in the thickener supernatant passes along to
the SFBW settling basins.
Recommendation: Consider evaluating the use of a polymer to improve
clarification in the SFBW settling basins and the quality of the supernatant water
recycled. Polymer addition might be particularly helpful during the times when
wash water from cleaning out the five main WTP sedimentation basins is directed
to the SFBW settling basins (note that Recommendation No. 1 above suggests
directing that wash water to the thickeners). Since the SFBW settling basin
supernatant might on occasion need to be discharged to the nearby creek (e.g., as
was done when there was a problem with the pump station at the UV disinfection
facility in July 2007), the issue of potential toxicity of the supernatant water
containing polymer should be reevaluated. This evaluation should also include an
assessment of any impacts from recycling polymer to the raw water reservoirs.
x

6. Issue: Recycle water turbidity levels on occasion were measured higher than the
raw water turbidity. However, the recycle flow averages only 5.0 percent of the
influent flow (maximum of 10.0 percent), and as such on those occasions
contributes a minor increase in turbidity for the influent water compared to that in
the raw water. Overall through the one-year period studied, there were 337 days
when recycle was occurring, and of those 337 days there were 43 occasions (12.5
percent) where the recycle water turbidity level exceeded that measured for the
raw water. Furthermore, of the times when recycle turbidity was greater than for
raw water, recycle turbidity was > 4 NTU on only 13 occasions (3.6 percent of all
sample days), and only 23 occasions where recycle turbidity was > 3 NTU (6.8
percent of all sample days). Raw water turbidity averaged 5.5 NTU during the
year.
Recommendation: Some type of informal goal for the level of recycle water
turbidity may be appropriate. One goal would be to establish a recycle water
turbidity maximum value, such as 4.0 or 5.0 NTU. Alternatively, the maximum
could be set at the influent turbidity, but this is a harder operating goal to monitor
and maintain and during times of low influent turbidity could be difficult to
achieve.
xi

v
ASSESSMENT OF RALEIGH'S RECYCLE SYSTEM
CITY OF RALEIGH, NORTH CAROLINA
OBJECTIVES AND APPROACH
This report provides an evaluation of the recycle system employed at the E.M. Johnson
water treatment plant (WTP). The overall objectives of this project are as follows:
Evaluate the existing recycle system and make any recommended improvements
• Offer opinions as to the acceptability of the current recycle system with respect to
water quality and operational impacts
Evaluate the state requirements for the recycle system
• Identify additional data collection needs
In order to evaluate the recycle system's possible impacts on water quality, EE&T and
the City worked together to gather historical data. That data were then reviewed in detail to
evaluate impacts. Fortunately, the City has a large database that allowed for this evaluation. We
often do not find that cities are as productive in collecting data on recycle systems as Raleigh has
been. The staff should be commended for their efforts in this area.
The first step was to obtain and review plant schematics and existing data on the residuals
system, recycle quality, reservoir quality, and plant operating data. These data were then
compared to recommendations in the AWWA report "Self Assessment of Recycle Practices"
previously prepared by EE&T, Inc. (Cornwell, et al., n.d.), following the flowchart provided in
that report for performing an evaluation of a recycle system. Additional guidance was obtained
from the Awwa Research Foundation report on "Water Treatment Residuals Engineering"
(Cornwell 2006) and the US Environmental Protection Agency's "Implementation Guidelines for
the Filter Backwash Recycling Rule (FBRR)" (USEPA 2002). A site visit was also conducted.
The evaluation process called for in the AWWA guidance examines raw water, recycle
water, combined influent, settled water, filtered water, and finished water quality over time. If
the finished water quality is not variable under normal or worst -case conditions, or if that
1

variability is not caused by recycle, then the recycle stream is not causing adverse perturbations
in finished water quality, and no further action would be recommended.
For this analysis, water quality and flow data were obtained primarily for a full one-year
period, from March 1, 2006 through February 28, 2007. The recycling of Spent Filter Backwash
Water (SFBW) settling basin supernatant was started on February 9, 2006 (data collection for
that water started on the same day); prior to that the flow was discharged to the nearby creek. As
such, the first full month of data collection was in March 2006. The following primary scenarios
were considered to help determine if recycling of the treated SFBW has had any adverse impacts
on treated water quality:
1. Comparison of water quality during periods with and without recycle: recycling
was discontinued from June 7 to 19, 2006 and August 1 to 14, 2006, and during
those periods the filter backwash sedimentation basin supernatant was discharged
to a nearby unnamed tributary of Honeycutt Creek. The June 7 to 19 period was
used to fulfill compliance with requirements set by the North Carolina
Department of Environment and Natural Resources (NCDENR 2005), and the
August 1 to 14 period resulted because the recycle pumps couldn't keep up with
the backwash rates due to excessively high consumer demand during this time
(Figure 2). These two 2-week periods were compared to results from the rest of
the year, with focus on the few weeks immediately preceding and following each
of those two periods.
2. Normal vs. worst -case conditions were examined. `Worst -case' conditions are
defined in the AWWA manual as times when recycle has the most potential to
impact water quality. The following conditions were evaluated.
• High water production (high flow): the highest influent flows were over
70 mgd (Figure 2), and occurred on July 17-18 (up to 75.2 mgd) and eight
days in August (up to 72.5 mgd)
High influent turbidity: possible periods include June 15 — 28, 2006 (>20
NTU; including during and immediately following the June 7 - 19 period
of no recycle); late April — mid May 2006 (up to 14 NTU), a couple days
2

in the month of December 2006 (6.1 — 13.2 NTU), and February 2007 (10
—12 NTU)
• High Temperature (for disinfection by-product (DBP) formation): month
of August (26.6 — 30.1 °C; avg. 28.1 °C) — this period coincided in part
with the period of no recycle on August 1-14, 2006
• Substantial change in operations: doubling of the ferric sulfate dose (it
was increased from 58.8 to 110 mg/L during December 10 —14, 2006)
• Low water production (low total flow) with recycling was also considered
since the percentage of recycle in the influent would be highest during low
production. The lowest total flows occurred in the winter (December —
March). However, flow data show that the percentage of recycle water
was consistent throughout the year (Figure 3), and thus no specific period
could be examined where the recycle water provided a larger than normal
relative contribution to the overall WTP influent flow. This analysis
would have to be performed on a day to day basis as opposed to selecting
longer periods of time to be representative of relatively low and high
periods of percent recycle
Each of these scenarios is discussed below in terms of its potential impact on a series of
different water quality parameters. The comparative analysis focused on different treatment
process streams — raw lake water, the recycle stream, the WTP influent (mix of raw lake water
and recycle stream), settled water, filtered water, and finished water. The impact of the recycle
stream on filtered water quality could potentially be a determining factor for either practicing or
discontinuing recycle of certain residual streams, or may indicate the need for additional
treatment prior to recycle. Settled water was studied to identify potential recycle impacts on the
primary coagulation and clarification process. Settled water quality can vary more than filtered
water quality and, therefore, may provide a clearer indication of potential recycle impacts.
Settled water data were available for two parameters only: turbidity from July 1, 2006 through
February 1, 2007, and Total Organic Carbon (TOC) from January 5 through March 15, 2007.
3

BACKGROUND
The impact analysis is presented on a contaminant by contaminant basis. The
contaminants evaluated were turbidity, TOC, manganese, iron, total coliform, HPC, suspended
solids, THMs and HAAs, and protozoa. In some cases only limited data could be analyzed.
When possible, the contaminant data were analyzed in accordance with the criteria and
evaluation factors listed above.
Recycle System
The City of Raleigh's E.M. Johnson water treatment plant (WTP) is rated for a capacity
of 86 mgd in April through October, and 78 mgd for November through March. The amount of
water treated averaged 52.5 mgd during the period from March 1, 2006 through February 28,
2007. The plant uses ozonation for primary disinfection (to help meet -disinfection by-product
(DBP) regulations), ferric sulfate coagulation and clarification (five sedimentation basins), high -
rate sand filtration (22 filters; up to 5.5 gpm/fl ), and chloramination for residual disinfection. In
the month of March chlorine is used instead of chloramines. Powdered activated carbon (PAC)
is also occasionally used. Raw water is obtained from Falls Lake.
Raw lake water and recycled water are combined in each of two raw water reservoirs (the
East and West Reservoirs), both with a rated capacity of about 70 million gallons. With an
average WTP influent flow of 52.5 mgd (combined from both reservoirs), each reservoir
provides approximately 2.7 days of detention time. Potassium permanganate or sodium
permanganate is added to the raw water lines before the two raw water reservoirs for oxidation of
organics and taste- and odor -causing compounds (and has been since the early 1990s).
Permanganate is generally not used at the same time as ozone.
A schematic of the recycle and residuals management system is provided as Figure 1.
There are two primary waste streams generated by the WTP processes: sedimentation tank
blowdown and filter backwash. Sedimentation tank blowdown is intermittent, occurring
approximately once per hour, and is conveyed by gravity to three thickeners. Polymer (Praestol
A3025L, Ashland Specialty Chemical, Greensboro, NC) is introduced at the thickeners to aid
in
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RALEIGH RESIDUALS SYSTEM
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Figure 1 Schematic of recycle/residuals system (as of June 2007)

in sludge blanket formation and maintenance. Thickener effluent is conveyed by gravity to the
two filter backwash sedimentation basins (described below) on a continuous basis. Thickener
sludge is pumped to sludge blending tanks and then dewatered through belt filter presses.
The same type of polymer (Praestol A3025L) is introduced before the filter presses to
aid in dewatering. Belt filter press filtrate and spent spray wash water are pumped to the sanitary
sewer through the sewer pump station. In addition, there is a spray stream used to clean the
solids conveyor belt ("conveyor belt spray down"), and that stream is also pumped to the sanitary
sewer through the Sewer Pump. The filter press solids are stored in one of the open outdoor mud
cake storage pad/drying beds (other drying beds are currently unused), and underdrain liquid
from all of the drying beds is pumped to the sanitary sewer through the sewer pump station. The
current system for filter press cake handling requires the cake be handled twice — once to move it
to the storage area, and a second time to load it onto the 20 cubic yard trailers used by the hauler.
Spent filter backwash (including filter to waste) is conveyed by gravity to two filter
backwash sedimentation basins (the North and South Basins). The spent filter backwash water
(SFBW) flow is intermittent, up to 22 times per day if each filter is backwashed once. Each filter
backwash typically produces 77,600 gallons of waste. Calcium thiosulfate, used for
dechlorination, is introduced to the SFBW prior to the North and South Basins. The thiosulfate is
added in case of an operational event that necessarily leads to discharging recycle water to a
nearby unnamed tributary of Honeycutt Creek (which drains back into Falls Lake). Caustic is
also added occasionally to the SFBW before the settling basins. SFBW clarifier sludge (from the
North and South basins) is collected and pumped back to the head of the residual waste treatment
system into the three thickeners.
The flow of supernatant from the SFBW clarifiers (the "recycle stream") is normally
continuous. During this study period, the recycle pump station pumps the North/South Basin
effluent (recycle stream) to the West Raw Water Reservoir, where it is combined with the raw
lake water to form the plant combined influent ("WTP influent"). The inlet for the recycle stream
into the reservoir is located fairly near the raw lake water inlet, and a good distance from the
outlet of the reservoir that carries water to the head of the WTP. Accordingly, there is a
reasonable level of mixing between the recycle water and raw water before it is used by the WTP.
R

A 26-MG on -site sludge storage lagoon is used occasionally to store solids resulting from
cleaning out the SFBW settling basins. The cleaning is done approximately once per year, but has
not yet been done since recycling started in February 2006. The solids remain in the lagoon until
dredged and hauled off -site.
On July 5, 2007 (subsequent to the period of data reviewed for this report), two
improvements were made to Raleigh's recycle system. First, a new ultraviolet (UV) disinfection
treatment system was started up to provide a high level of disinfection for the supernatant from
the filter backwash settling basins. The UV will help further remove coliform bacteria from the
recycle stream, and it is also particularly effective for sterilizing Cryptosporidium and Giardia,
depending upon the delivered dose. Secondly, a new pump station (three 8-mgd pumps) was
installed to pump the treated spent filter backwash water to both the East and West raw water
reservoirs. While the new pumping arrangement won't necessarily result in additional dilution
of the recycle water with the raw lake water (since water from the two reservoirs is combined
anyway prior to entering the WTP), it does provide sufficient pumping capacity such that during
periods of relatively high flow all of the filter backwash settling basin supernatant can be
pumped to the raw water reservoirs (that was not always the case previously, as in August 2006
the flow of supernatant was too high for the old pumps to handle and the supernatant was
discharged to the creek for two weeks). Both of these improvements are expected to provide an
additional safeguard for recycling the treated streams to the head of the WTP.
Lastly, piping and valve improvements were made on May 18, 2007 to discharge the
drying bed underdrain water to the sewer system. Previously the underdrain water was pumped
to the splitter box just before the three thickeners, but a leaking valve allowed some of that water
to be directed to the SFBW settling basins, potentially resulting in unnecessarily elevated
manganese levels in the settling basin supernatant.
Data Used In This Evaluation
This assessment is based on data provided by the City of Raleigh Public Utilities
Department. Data were obtained mostly for the one-year period from March 1, 2006 through
February 28, 2007, as described below. The data used in the plots presented below were
h

0.
obtained mostly from the Recycle data sheets, and were supplemented where needed and
appropriate with data from the Monthly Reports or TOC data sheets. The data evaluated
included at minimum the following:
Recycle data sheets (March 2006 — February 2007)
• Monthly reports included data for Falls Lake Raw Water, Treated Waste Effluent
— Recycle (only through September 2006), Treated Waste Effluent - Discharge,
Water Plant Influent (including recycle), and Water Treatment Plant Finished
Water
• The two "Treated Waste Effluent" samples are of the supernatant from the
backwash water settling basins. The "Treated Waste Effluent — Recycle" samples
are obtained before the suction side of the pump, and the "Treated Waste Effluent
— Discharge" samples are obtained on the downstream of the pump — about 500
feet downstream from the "Treated Waste Effluent — Recycle" samples
Includes daily data for flow, turbidity, pH, temp, iron, manganese, total organic
carbon (TOC), dissolved organic carbon (DOC), total coliform, and heterotrophic
plate count (HPC) (Mar — Sept 2006) or E-Coli (Oct 2006 — Feb 2007)
• Includes weekly data for settable solids and/or total suspended solids (TSS), and
total solids (TS)
• Includes monthly data for total trihalomethanes (TTHM) and haloacetic acids
(HAA5) in the finished water; monthly data for Cryptosporidium and Giardia in
the raw lake, recycle, and influent water; and slightly more frequent data for UV-
254 and SUVA (raw lake water, recycle water, influent water, and finished water)
Monthly reports (March 2006 — February 2007)
• Raw and finished water:
PHYSCHEMI spreadsheet: daily data for turbidity (also settled water for
July — December), color, pH, carbon dioxide, alkalinity, hardness

i
- PHYSCHEM2 spreadsheet: daily data for Mn, Fe, fluoride, and chlorine;
weekly data for chloride
DBP precursor spreadsheet: TOC and alkalinity (monthly averages)
• Finished water only: PHYSCHEM2 spreadsheet: nitrate and silica
(approximately weekly)
• Settled water only: PHYSCHEMI spreadsheet: turbidity (daily) - available for
July 2006 - February 2007
• Temperature: Raw water (PHYSCHEMI spreadsheet) and finished water
(PHYSCHEM2 spreadsheet)
• Microbiological Operations Report: Colilert MPN and coliforms/100 mL for raw;
total plate count and Colilert MPN for filtered and finished water
• DBP Precursor Removal Performance #1 report: monthly TOC and alkalinity
(source water and treated water)
• DBP Precursor Removal Performance #2 report: monthly bromide and bromate
for finished water, and monthly bromide in source water
Distribution system: chorine residual, total coliform, E-coli
• Turbidity Monitoring Report: readings 6 times per day
• Residual Disinfectant (Chlorine) Monitoring Report: readings 6 times per day for
finished water
• Plant Operations/Filter runs: daily data for influent flow, filter run length, filter
washing, chemicals used
• Plant Operations - Attachment: daily data for influent flow, ozone used
• "LABMrATTACHED" sheet: daily summaries for turbidity (raw), pH (raw,
filtered, and finished water), alkalinity (filtered and finished), Mn (finished),
chlorine (finished), and sludge water produced
TOC data sheets (Jan 2006 - Mar 2007)
• TOC data: WTP influent and finished water for all of 2006 (daily data; M-F is
regular, weekends are composite samples)
E

• "Special TOC data": for December 2006 — March 15, 2007 includes TOC data
for source, influent (labeled as `raw'), and finished water; also influent alkalinity;
includes settled water TOC for Jan 5 — Mar 15, 2007
Sampling Locations
The different types of water mentioned above were obtained at various sampling points
as follows:
• Raw lake (source) water: sampled from one of the two raw water lines leading
from the lake to the raw water reservoirs (the 36-inch pipe, not the 54-inch pipe);
this sample is pre -impoundment and pre -permanganate addition
• Influent water (combined raw lake water and recycled water): taken at the venturi
meters entering the WTP. This water is post -reservoir (water combined from both
of the raw water reservoirs), post-preoxidant (e.g., post -permanganate addition
and post -ozone when used), post -powdered activated carbon (when used), pre -
ferric sulfate, and before any other chemical addition
• Recycle water: sampled just before SFBW clarifier supernatant pumps
• Settled water: sampled between the clarifiers and sand filters
• Filtered water: taken right after the filters, after all filter effluent is combined
Finished water: clearwell effluent just before it is pumped into the distribution
system; this is the final treated water after addition of chlorine, caustic, fluoride,
corrosion inhibitor, and ammonia
10

RESULTS OF DATA ANALYSIS
Data are presented for the following parameters:
• Flow (Figures 2 — 3)
• Turbidity (Figures 4 —10)
• Total organic carbon (Figures 11-14)
• Manganese (Figures 15 — 23)
• Iron (Figures 24 — 27)
• Total coliform (Figure 28)
• Heterotrophic plate count (Figure 29)
• Total suspended solids (Figure 30)
• TTHM and HAA5 (Figures 31— 33)
• Cryptosporidium and Giardia (Table 1)
Flow
The amount of finished water produced during the one-year period (March 1, 2006 —
February 28, 2007) ranged from 35.5 to 66.3 mgd, and averaged 48.4 mgd. Treated water flows
(influent to the WTP) ranged from 38.4 to 75.2 mgd, and averaged 52.5 mgd (Figure 2). Recycle
flows averaged 5.2 percent of the total influent flow (range of 0.0 to 10.0 percent), corresponding
to an average of 2.9 mgd (range of 0.0 to 5.0 mgd) (Figure 3). The daily amount of water
recycled never exceeds 10 percent of the same day's production.
As expected, the highest flows experienced during the period were in July and August
(Figure 2). The highest influent flows were over 70 mgd, and occurred on July 17-18 (up to 75.2
mgd) and eight days in August (up to 72.5 mgd).
11

Turbidity
Recycle water turbidity averaged 2.61 NTU, with a range of 0.65 to 19.7 NTU (with one
exception of 43 NTU on January 29, 2007), throughout the one-year period of March 1, 2006
through February 28, 2007. Recycle water turbidity is typically lower than the raw lake water
turbidity (Figures 4 and 5), and thus typically would have no adverse impact on the turbidity of
the influent water. However, there were a few occasions where recycle water turbidity was
higher than the raw lake water turbidity, as discussed below.
In terms of periods of recycle water turbidity being higher than the raw lake water
turbidity, Figure 6 focuses on turbidity for just those two waters (for values up to 20 NTU).
Other than twelve (12) individual days scattered during the year, there were two main times
when recycle water turbidity occasionally exceeded raw water turbidity: December 2006 through
January 2007, and July 2006. Each of these cases is discussed below.
1. December 2006 through February 2007: During these three months WTP staff
were cleaning out the five primary sedimentation basins, and the wash water was
directed to the SFBW settling basins. As such, recycle water turbidity was highly
variable throughout those three months, and there were ten (10) days where
recycle turbidity was greater than raw lake water turbidity. Nonetheless, this
appeared to have no adverse impact on finished water turbidity, as that was at a
maximum of 0.12 NTU during those 12 days, and ranged only from 0.07 to 0.14
NTU during the whole three months.
To lessen any potential impact of this wash water, WTP Standard
Operations Procedures (SOPs) dictate that no filters will be backwashed during
times that sedimentation basin wash water is directed to the SFBW settling basins
for at least three (3) hours afterwards. While it would be better if that wash water
was directed to the three thickeners in order to receive an additional clarification
step (and the polymer used in the thickeners), the current piping system does not
allow for this arrangement.
12

2. July 2006: There were 21 days during this month where recycle water turbidity
exceeded that in the raw water, with the differences being relatively small,
ranging from 0.1 to 2.6 NTU. During this period raw water turbidity was low
relative to historical values, averaging 2.6 NTU (median of 2.3) compared to an
average during that year of 5.5 NTU (median 3.8). Furthermore, recycle water
turbidity never exceeded 5.0 NTU at any time during the month. Given that the
recycle flow contribution is usually around only 5 percent of the total influent
flow, these minor excursions where recycle water turbidity is relatively low but
slightly greater than raw water turbidity should have little or no adverse impact on
the treatment system.
3. Twelve (12) days scattered throughout the one-year period examined: Of these
12 days, where recycle water turbidity exceeded that of the raw water, on only
one occasion (13.7 NTU difference) did recycle water turbidity exceeded that of
the raw water by more than 1.7 NTU. Furthermore, the raw water turbidity on all
of these 12 days was lower than normal, averaging 1.7 NTU with a high of 2.6
NTU. Examining the finished water turbidity values for these 12 shows no
impact from the recycle turbidity being slightly higher than the raw water, as only
once did finished water turbidity go above 0.12 NTU (and that was 0.18 NTU on
a day when recycle was only 0.1 NTU higher than the raw water turbidity). As
noted above, the recycle flow contribution is usually around only 5 percent of the
total influent flow, further supporting the lack of adverse impact from these minor
excursions where recycle water turbidity is slightly greater than raw water
turbidity.
Overall through the one-year period studied, there were 337 days when recycle was
occurring, and of those days there were 43 occasions (12.5 percent) where the recycle water
turbidity level exceeded that measured for the raw water. Furthermore, of the times when
recycle turbidity was greater than for raw water, recycle turbidity was > 4 NTU on only 13
occasions (3.6 percent of all sample days), and only 23 occasions where recycle turbidity was > 3
NTU (6.8 percent of all sample days), raw water turbidity averaged 5.5 NTU during the year.
13

In terms of periods of relatively high influent turbidity, during the one-year period
examined (March 1, 2006 — February 28, 2007) there were four occasions when influent turbidity
rose above 10 NTU (Figures 4 and 5): (1) June 17 — 28, 2006 (21 — 29 NTU); (2) late April —
mid May (up to 14 NTU); (3) two days during the month of December (up to 13 NTU); and (4)
most of the month of February 2007 (10 —12 NTU). Each of these periods is discussed below:
1. June 17 — 28, 2006: Between June 14 — 16, influent water turbidity rose from <
10 up to 29 NTU, and this spike corresponded to an increase in raw water
turbidity from <2 up to 45 NTU (Figures 5 and 7). These high levels
corresponded with a large storm event on June 14, 2006, when approximately 6 to
8 inches of rain fell within a day. These high turbidity levels began dropping after
these peaks but remained relatively high for the rest of the month of June. Raw
water TOC (Figure 11) and iron (Figure 21) concentrations also increased
subsequent to this storm event.
Note that recycling had been discontinued (to comply with NCDENR
requirements) during the time of the large increase in raw and influent water
turbidity (there was no recycling from June 7 to 19), and thus recycling could not
be contributing to the influent water turbidity. As such, the large increases in raw
water and influent turbidity were clearly caused by the large storm event
mentioned above, not the restart of recycle on June 20. Even after recycle
restarted on June 20, the recycle water turbidity remained at or below 3 NTU, and
thus could not be the cause of the relatively high influent water turbidity that was
experienced throughout the rest of June. The data also indicate that all finished
water turbidity were < 0.15 NTU during the storm event and for the next couple
of weeks following that.
Note that the raw water turbidity reached its peak on June 16, and the
influent turbidity did not reach its peak until June 17 — 18. This difference in
timing is a result of the detention time in the raw water reservoirs, as the inlet and
outlet are at opposite ends of the reservoir(s), and thus this lag period of one to
14

two days is the time it takes the new raw water to reach the influent inlet to the
WTP.
Lastly, this large increase in influent turbidity (Figure 7) appeared to cause
the relatively high levels of settled water turbidity observed when that data was
starting to be collected on July 1 (Figure 8).
2. Late April — mid May 2006: During late April to mid May 2006, influent
turbidity rose from about 5 NTU up to 14 NTU and back down again to 5 NTU
(Figures 4 and 5), but this increase was not accompanied by an increase in either
recycle water or raw lake water turbidity. As such, this spike in influent turbidity
does not appear affected by the recycle water, but can not be fully explained given
the lack of correlation with raw water turbidity levels.
3. November 2006 to February 2007: In late 2006, the influent turbidity steadily
rose from about 2.5 NTU in mid -November up to 12 NTU by mid -February
(Figure 9). The rise in influent turbidity is apparently caused by a similar rise in
raw lake water turbidity, both likely due to frequent rain events (TOC also
increased). During that period the recycle water turbidity also generally increased
(even going as high as 43 NTU; second highest value was 20 NTU), but showed
much more variability than the steadily increasing trends of the raw and influent
water turbidity. The start of the increase in recycled water turbidity occurred over
one week after the raw lake water turbidity started to increase (Figure 9), and so it
would appear that the cause of the influent turbidity increase at that time is not
due to the recycle practice but rather to changing raw water conditions. As noted
previously, the ferric sulfate dose was nearly doubled between December 10 and
14. Though there is a fair amount of variability in the recycle water turbidity
following that change, that variability had already been observed since the
beginning of December (Figure 9), and thus is not likely attributable to the change
in ferric sulfate dose. Furthermore, settled water turbidity, which had been slowly
but steadily increasing since the beginning of November, decreased slightly after
the change in ferric sulfate dose had been made (Figure 9), indicating a slight
improvement in water quality. Lastly, as described above, the fluctuations in
15

recycle water turbidity are likely caused by the occasional introduction into the
SFBW settling basins of wash water from the five primary sedimentation basins.
4. February 2007: In this case influent turbidity stayed around 10 to 12 NTU for
the whole month (Figures 4 and 5). This was not a large change from recent
values, however, as it had been mostly around 6 to 9 NTU in December 2006 and
7 to 9 NTU in January 2007 (Figures 4 and 5). As was the case for December
2006 (discussed above), the relatively high influent turbidity levels correlated at
the same time to relatively high raw lake water turbidity levels. Recycle water
turbidity during this period varied greatly, as it had since the beginning of
December 2006, as discussed above.
In terms of periods of relatively high finished water turbidity, there were only five days
during the year where it reached as high as 0.3 NTU, and those were all between August 11 and
15 (0.30 to 0.34 NTU). Two of those values were obtained on the second and third days after
recycling was restarted following a two -week period of no recycle (August 1-14, 2006), and the
other three values were from a few days before that two -week no -recycle period ended. Can
these turbidity values above 0.3 NTU be attributed to the restart of the recycle? Apparently not,
as the evidence suggests otherwise. Primarily, no substantial difference is shown in settled or
finished water turbidity between the times during and immediately before and after the August 1
— 14, 2006 period of no recycle, and though a slight increase in both values is shown in August
2006, that increase started near the end of the no -recycle period before recycle was restarted
(Figures 7 and 8).
Further examination of finished water turbidity (Figure 5) shows that throughout the year
it typically was around 0.1 NTU, but an increase occurred around June 16, 2006, with the level
rising up to 0.2 to 0.3 NTU and staying around there until it started to decrease again around
August 17, getting down to approximately 0.1 NTU on around September 3, where it stayed
throughout the rest of the period examined through the end of February 2007. As discussed
above, the start of this approximately 2.5-month period of relatively high finished water turbidity
corresponded to a large storm event on June 14, 2006, when approximately 6 to 8 inches of rain
16

fell within a day (note in Figure 5 the very high raw lake water and influent turbidity levels at
that time).
Finished water turbidity is compared to recycle water and settled water turbidity in Figure
10 (similar to Figure 5). Note that there is a rise in recycle water turbidity in late June and July
2006 that occurred at the same time as the rise in finished water turbidity. As mentioned above,
it seems clear that the large storm event, which occurred just a few days before recycle restarted
on June 20, 2006, was responsible for the large increase in raw and influent water turbidity.
Furthermore, the subsequent 2.5-month period of relatively high finished water turbidity does not
appear to be caused be the restart of recycle because of the following factors:
1. There was no beneficial impact in stopping recycle on June 7 (Figure 10)
2. The recycle water contributes only about 5 percent of the influent flow to the
WTP
3. The increase in finished water turbidity corresponded to a decrease in settled
water turbidity in early July 2006 (Figure 8), and if recycling was a contributing
adverse factor then the settled water turbidity also should have been affected.
Instead, it appears that the period of relatively high finished water turbidity was
started by the large storm event (and corresponding high influent turbidity) and
continued because of operational factors related to the sand filters
4. The increase in finished water turbidity noted started a few days before recycle
restarted, and any impacts from restarting recycle would not have been expected
to be observed not until a few days after the start due to mixing of recycle water
with raw lake water in the raw water reservoirs and the corresponding lag period
in that recycle water reaching the influent inlet to the WTP
5. In March 2006 there was a similar rise in recycle water turbidity but with no
change in finished water turbidity (Figure 10)
Accordingly, despite the fact that recycle water turbidity was somewhat elevated in late June and
July 2006 (Figure 10), the storm event in mid -June and subsequent operational factors for the
sand filters are much more likely the cause of the increase in finished water turbidity in the time
following the June no -recycle period than is the restart of the recycle stream.
17

In terms of comparing periods of recycle and no recycle, settled and finished water
turbidity did not visibly vary between these two different times (Figure 8), suggesting no impact
from recycling on either settled or finished water turbidity. For example, during the August 1 —
14, 2006 period of no recycle, settled water turbidity ranged from 0.25 to 0.46 NTU, while
during the two weeks before and after that period it ranged from 0.20 to 0.45 NTU (Figures 7
and 8). Settled water turbidity levels for all of July through December 2006 (Figures 4 and 5)
ranged from 0.19 to 2.0 NTU, with an average of 0.68 NTU. During the August period of no
recycle, finished water turbidity ranged from 0.19 to 0.31 NTU, while during the two weeks
before and after that period it ranged from 0.12 to 0.34 NTU (Figures 7 and 8).
The influent turbidity does begin to rise slightly during the latter stages of the August
two -week no recycle period (1.6 up to 2.5 NTU), then continues to rise up to 6.4 NTU before
falling again in late August. During that rise, however, recycle water turbidity (Figure 7)
remained the same or decreased (ranged from 1.0 to 2.3 NTU during August 15-31, 2006), and
was consistently below the raw lake water turbidity (2.0 to 4.9 NTU). With a slightly lower
turbidity level and a much lower flow contribution compared to the raw lake water, the recycle
water does not appear responsible for the August perturbations in finished water turbidity above
0.3 NTU, nor for the rise at that time in influent turbidity.
Examining the June 7 — 19, 2006 period of no recycle, finished water turbidity did not
vary substantially between the periods before or during the time of no recycle (Figure 8) (settled
water turbidity data were not available for this period). While there is a slight increase in
finished water turbidity from 0.09 to 0.15 NTU in the two weeks subsequent to this period
(Figure 8; and as discussed elsewhere, finished water turbidity continued to rise after that time),
examination of Figure 7 shows a large increase in raw lake water and influent water turbidity
during the latter third of the no -recycle time period running from June 7 to 19. These increases
were fairly substantial, and were caused by a large storm event.
Total Organic Carbon
Total organic carbon results are presented as an indication of DBP formation potential in
Figures 11 to 14. Throughout the one-year period of March 2006 through February 2007,
18

influent TOC changed in accordance with the raw lake water TOC, and recycle water TOC was
consistently less than either of those (Figure 11). Recycle water TOC usually rose during
periods when raw water TOC was rising, as did finished water TOC but to a much lesser degree
(Figure 11). Since the recycle TOC was always less then the raw TOC, recycle can only lower
the influent TOC, not raise it.
The overall efficiency of the treatment plant at removing TOC is shown in Figure 12
(influent vs. finished water levels). The second two -week period of no recycle (August 1 to 14,
2006) showed no substantial difference in TOC removal percentage than the weeks immediately
before or after that period (Figure 12). The first two -week period of no recycle (June 7 - 19,
2006) appeared to show a slight drop in TOC removal efficiency, thus indicating no adverse
impact from the recycling stream (Figure 12). While that same period corresponded to a slight
increase in finished water TOC (from about 2.1 up to 2.8 mg/L; Figure 13), that result is
correlated to an increase in both raw lake water and influent water TOC resulting from the big
storm event in June 2006.
TOC results focusing on the no -recycle periods are presented in Figure 13. Here it is
clear that the influent and finished water TOC did not change as a result of the lack of recycle.
Recycle water TOC varied more than did that for the raw, influent, or finished water, but was
always at a lower concentration than the raw or influent water (Figure 13). As such, the recycle
water it is not contributing any increase to the influent TOC level. Note that the increase in
ferric sulfate dose (between December 10 and 14) apparently helped to improve TOC removal
efficiency from around < 60 percent up to 70 percent, as evidenced in Figure 12.
Settled water TOC data were available for January through mid March 2007, and are
plotted in Figure 14. During that period the settled water and finished water TOC levels were
very similar and steady, ranging only from 2.1 to 3.1 mg/L. The influent TOC was typically
similar to but slightly less than the raw water levels, with both ranging between 7.3 and 10 mg/L.
Recycle was ongoing during that whole period (Jan - Mar 2007). There is a good increasing
correlation for both TTHM and HAA5 with the finished water TOC (but not with influent water
TOC), as discussed below in the section on TTHMs and HAA5.
19

Manganese
Manganese results are presented in Figures 15 to 23. Manganese levels for lake water,
recycle water, permanganate addition, influent water, and finished water are shown in Figure 15
for the one-year period of March 2006 through February 2007, and Figure 16 focuses on the
finished water and raw lake water data for that period. Finished water manganese concentrations
were almost always lower than or equal to the raw lake water manganese (with only one
exception on May 23, 2006), and ranged from 0.00 to 0.05 (only twice did it go above 0.03
mg/L), and averaged 0.006 mg/L (Figure 16). Raw lake manganese levels were typically below
0.15 mg/L (full range of 0.01 to 0.33 mg/L), and averaged 0.06 mg/L for the year (Figure 16).
Potassium permanganate (KMnO4) or sodium permanganate (NaMnO4) is added
seasonally to the raw water lines before the raw water reservoirs for oxidation of organics and
taste- and odor -causing compounds (and has been since the early 1990s). The amount of
permanganate used is based on a 4-hour manganese demand test. KMnO4 was used from
January 1 - July 4, 2006 and February 1 — 11, 2007; NaMn04 was used November 13, 2006 —
January 31, 2007, and then again on February 12 - 28, 2007; and neither oxidant was used from
July 5 - November 12, 2006.
When used, the permanganate typically contributes the bulk of the manganese in the
influent water, and the influent manganese levels vary substantially over time as the desired
doses changed (Figures 15 and 17). The WTP influent manganese concentration reached as high
as 2 mg/L when permanganate was added (Figures 15 and 17), and only up to 0.8 mg/L (usually
< 0.6 mg/L) when it wasn't used (Figures 15, 17, and 18). Data in Figures 15 and 17 show that
when permanganate is used, the concentration of Mn added and the measured influent levels
correlate reasonably well. The changes in influent manganese level also followed the changing
pattern of influent turbidity, as shown in Figure 17. That pattern between influent turbidity and
influent manganese exists whether potassium permanganate was being added or not (Figure 17).
Figure 18 focuses on the period of no permanganate addition, showing the manganese
concentrations in the raw lake water, recycle water, and influent water. Recycle manganese
concentrations are consistently higher than those in the raw lake water throughout this period
(and also during the rest of the year when permanganate was used). The recycle water
20

manganese concentrations are also higher than those in the influent water during this period
(Figure 18). During the rest of the year when permanganate is used the recycle concentration
varies in relation to the influent level, sometimes being higher and sometimes lower than the
concentration in the influent (Figure 15).
Interestingly, one substantial increase in the concentration of Mn in the influent water
occurred during the second week of the August 2006 two -week period of no recycle (and when
no permanganate was being added), as shown in Figure 18. Since there was no recycle occurring
at this time, this increase in influent Mn can not be attributed to the recycle water. However, it
appears to be directly related to a corresponding increase in raw water manganese concentration
(Figure 18).
Figure 19 presents the manganese levels during and around the two time periods of no
recycle, the latter of which was also a period of no permanganate addition, and Figure 20 focuses
on the finished water for that same time period. The lack of recycle did not result in lower levels
of manganese in either the finished water (Figures 19 or 20) or the influent water (Figure 19).
While the measured finished water manganese concentrations were 0.0 mg/L during the whole
June 7 — 19 period of no recycle, it had already dropped to that level a few days before the
recycling was stopped (Figure 20). As such, recycle did not appear to adversely affect
manganese levels in the finished water during this period.
Since the recycle water manganese concentrations are typically higher than the raw lake
water levels, a mass balance analysis was performed to compare the manganese loading rates of
the various sources (raw lake water, recycle water, and permanganate addition). Concentration
values were multiplied by flow rates to calculate the total daily mass in each water stream. The
results are shown in Figure 21, which presents the daily mass loading (in kg of Mn) for the added
permanganate, raw lake water plus recycle water, and the influent water (note that Figure 21 is
the mass balance counterpart to Figure 15, which included concentration levels for the various
sources).
When permanganate is used, the dose added and the mass of Mn measured in the influent
correlate well, and the mass of manganese added is substantially well above the levels in both the
raw water and recycle water (Figure 21). Accordingly, the recycle stream does not contribute
any substantial amount of manganese to the influent water when permanganate is being used.
21

When permanganate is not used, the mass loading from the raw lake water plus recycle water
correlate roughly to the influent levels, (Figure 21), but this is not as good a correlation as that
between the permanganate dose and influent level when permanganate is added. In this case,
they are roughly the same level as they are during periods of no permanganate use (Figures 15
and 22).
Figure 22 shows the relative daily mass loadings of manganese for the raw lake water
and the recycle water, and in most cases their mass contributions of Mn to the influent water
were relatively equal, though the raw lake water contribution was at times higher. This is simply
a result of the higher concentration but lower flow contribution associated. with the recycle water
compared to the raw lake water.
The period where permanganate was not added (July 4 — November 12, 2006) is
examined in more detail in Figure 23. This shows that the Mn mass loading from the recycle
water was at times less than, at times roughly equal to, and at times greater than that of the raw
lake source. Note that Figure 23 is the mass balance counterpart to Figure 18, which included
concentration levels for the various sources during the period of no permanganate addition.
Iron
The primary source of iron in the water is expected to be from the use of ferric sulfate as
the primary coagulant, and iron concentrations in the recycle water were typically higher than
that in the raw lake water, WTP influent, or finished water (Figure 24). Ferric sulfate is added
downstream from the collection point for the WTP influent samples. The applied ferric sulfate
dose over time is plotted in Figure 25. The dose was deliberately nearly doubled between
December 10 and 14, 2006.
Figure 26 focuses on the level of iron in the finished water from March 2006 through
February 2007, and shows that it was usually below 0.05 mg/L, and was always 0.10 mg/L or
below. Finished water iron levels varied from 0.0 to 0.10 mg/L, averaging 0.018 mg/L with a
median of 0.10 mg/L (Figure 26). Focusing around the two periods of no recycle, Figure 27
presents the levels of iron in the recycle water, raw lake water, influent, and finished water.
Removal of iron (levels in the finished water) did not seem to be affected by the recycle practice.
22

The upward spike in raw water iron concentration observed in June 2006 (Figure 27) is
attributable to the large storm event that occurred then.
Total Coliform
Figure 28 presents the total coliform results for February through December 2006 for the
raw lake water, recycle water, and WTP influent. Total coliforms were measured as "absent" in
all finished water samples in 2006, illustrating the effectiveness of the chloramine/chlorine
disinfectant. Accordingly, the recycle practice apparently did not adversely impact finished
water coliform levels.
Recycle water coliform levels were usually below or near the levels measured in both the
raw lake water and influent water. One exception was the period of late April to May 2006,
where recycle coliform levels were above those found in the raw water (and similar to those in
the influent) (Figure 28). However, during that period there was no substantial change in the
influent coliform level (Figure 28), and none were detected in the finished water. As noted
previously, a UV disinfection system for the recycle water was installed in summer 2007 which
should provide for good disinfection of coliform bacteria.
Heterotrophic Plate Count
HPC is an indicator measure of the general bacteriological quality of the water. A
heterotroph is any organism that cannot make its own food and is therefore dependent on other
substances such as organic carbon for nutrition. Organisms measured using HPC methodologies
include bacteria, yeasts, and moulds.
Figure 29 presents the HPC results for March to September 2006 for the raw lake water,
recycle water, WTP influent, and finished water (after September HPC was no longer monitored,
and E. Coli was measured instead). Recycle water HPC was usually above or near the level
measured in the WTP influent, and the influent HPC was usually near or above the level in the
raw lake water (Figure 29). Thus in terms of HPC concentrations it appears the recycle water is
contributing some to the HPC loading of the influent water, but of course the recycle flow is
23

much less than that of the raw water. Furthermore, most of the time HPC was measured as <2
CFU/mL in the finished water, while on only 12 days during those seven months the level was
between 2 and 6 CFU/mL. Only once was HPC measured in the finished water above 6
CFU/mL, that being 56 CFU on April 23, 2006 (Figure 29), and that result did not correlate with
any perturbation in influent water HPC. HPC and E. Coli levels in the recycle water are
expected to be lower in the future with the installation of the new UV disinfection system in
summer 2007.
Total Suspended Solids
Figure 30 presents weekly data for total suspended solids (TSS) between March and
September 2006 for the raw lake water, recycle water, WTP influent, and finished water.
Finished water levels were usually reported as 0 mg/L, though on three occasions were measured
as 1 mg/L (Figure 30). TSS for the other water streams was slightly higher. Normally either the
raw lake water (range 1 — 6 mg/L; average 3.20) or influent water (range 0 — 14 mg/L; average
4.52) TSS level would be highest, with the level in the recycle water (range 0 — 5 mg/L; average
2.13) being lower than either of those (Figure 30). As such, the recycle stream is not adversely
contributing TSS to the influent water. No data were obtained during either the June or August
2006 two -week periods of no recycle, so direct comparison to those periods could not be made.
No seasonal trends were observed during the period of March through September 2006.
TTHM and HAA5
Total trihalomethanes (TTHM) and haloacetic acids (HAA5) were measured
approximately monthly in the finished water; results are presented in Figure 31. TTHM ranged
from 26.4 to 86.4 µg/L, and averaged 47.9 µg/L. HAA5 ranged from 19.1 to 66.7 µg/L, and
averaged 39.1 µg/L. As expected, the highest results were obtained in July and August, the two
warmest months. In terms of recycle water contribution, no DBP data were available for the
recycle water stream. However, the highest DBP results of the year were obtained on August 7,
2006 (83.4 µg/L for TTHM and 66.7 µg/L for HAA5), about half way through the two -week
24

period of no recycle. A TTHM sample obtained shortly before that period on July 27 measured
77.6 µg/L. Accordingly, the recycle stream is apparently not the cause of the relatively high
DBP results since the highest results were obtained during a period with no recycle occurring.
Finished water TTHM and HAA5 levels are compared to TOC concentrations for the
finished water in Figure 32, and to influent water TOC in Figure 33. There is a good increasing
correlation for both TTHM and HAA5 with the influent water TOC (Figure 33), but not with the
raw water TOC (Figure 32) due largely to the different treatment steps between the samples.
Only one sample day included both DBPs and settled water TOC, so no comparison could be
made there.
Cryptosporidium and Giardia
The USEPA Filter Backwash Recycle Rule is designed to help prevent the recycling of
key water quality constituents, particularly active protozoan pathogens such as Cryptosporidium
oocysts and Giardia cysts, to prevent potential contamination of the drinking water supply.
Monthly samples were collected and analyzed via USEPA Method 1623 for the raw lake water,
recycle water, WTP influent, and finished water. The data obtained are reported in Table 1.
Neither Cryptosporidium nor Giardia were detected in any of the monthly samples for the
finished water during the period of February 2006 through February 2007. The samples of the
other waters resulted in few detections of Cryptosporidium, and no detections of Giardia.
The positive Cryptosporidium samples were from the months of May, June, and July
2006 (Table 2). Standard analytical methods for Cryptosporidium are notoriously difficult and
unreliable, and the different results for the two types of recycle water samples reflect this
problem. Specifically, these two samples are of essentially the same water, obtained a mere
—500-feet apart on either side of the recycle pump (the "Treated Waste Effluent — Recycle"
samples are SFBW clarifier supernatant obtained before the suction side of the pump, and the
"Treated Waste Effluent — Discharge" samples were obtained —500 feet downstream on the
discharge side of the pump). On all three occasions where Cryptosporidium was detected, one of
these samples had a positive result while the other was not detected (Table 1). Given the
similarity of these two sample sources, similar results for each would have been expected.
25

Table 1
Measured Cryptosporidium and Giardia concentrations
Cryptosporidium
Giardia
Treated
Treated
WTP
Treated Treated WTP
Waste
Waste
influent
Raw
Waste
Waste
influent
Raw lake
Effluent -
Effluent -
(incl.
Finished
lake
Effluent -
Effluent -
(incl.
Finished
Date
water
Recycle
Discharge
recycle)
water
water
Recycle
Discharge
recycle)
water
2/20-28/06
0
0
0
0
0
0
0
0
0
0
3/21-28/06
0
0
0
0
0
0
0
0
0
0
4/24-25/06
0
0
0
0
0
0
0
0
0
0
5/22-31 /06
0
0.19
0
0.19
0
0
0
0
0
0
6/20-21 /06
0
0
0.10
0
0
0
0
0
0
0
7/17/06
0.10
0
0.10
0.29
0
0
0
0
0
0
8/15/06
0
0
0
0
0
0
0
0
0
0
9/13/06
0
0
0
0
0
0
0
0
0
0
10/23-24/06
0
NA
0
0
0
0
NA
0
0
0
11/28/06
0
NA
0
0
0
0
NA
0
0
0
12/12/06
0
NA
0
0
0
0
NA
0
0
0
1/16/06
0
NA
0
0
0
0
NA
0
0
0
2/13/06
0
NA
0
0
0
0
NA
0
0
0
1VULCs: 1Vt1 � nUL analy"LCU. 1 nC 1 rCULCU W USLC Z111Uem — 1CCcyc1C samples are arts W clarlller supernatant omamea UeIore the sucuon siae of the pump,
and the "Treated Waste Effluent — Discharge" samples were obtained —500 feet downstream on the discharge side of the pump.
26

Due to the expensive cost of these tests more frequent analyses was not practical, and
much more data are available for potential indicator parameters such as turbidity, total coliform,
and HPC, as discussed above. 'Importantly,- and despite the lack of any positive detection for
Giardia and infrequent detection of Cryptosporidium, a new UV disinfection treatment system
was installed for the treated recycle water stream in summer 2007 (Figure 1). UV disinfection
can be highly effective at inactivating both Cryptosporidium and Giardia, depending upon the
dose. Though there was no indication from the data examined that the recycle water has any
adverse impact on finished water quality, this additional treatment step may help to further
ensure a high -quality recycle water with no adverse impact on the microbiological quality of the
finished water.
27

SUMMARY
An extensive evaluation of the City of Raleigh's E.M. Johnson water treatment plant's
waste stream recycling system and related water quality data was performed to determine if the
recycling practice has any observable adverse -impact on finished water quality. The recycle
practice did not have any adverse impacts on finished water quality for any of the water quality
parameters examined. Parameters evaluated and discussed in this report include flow, turbidity,
Cryptosporidium, Giardia, total coliform, HPC, TOC, manganese, iron, TSS, THMs, and HAAs.
In fact, concentrations of several key parameters in the recycle water were less than that of the
raw water (e.g., turbidity, TOC, TSS), while in cases where the recycle water did have a higher
concentration than the raw water (e.g., Mn, Fe, HPC) there was no observable impact at any time
on finished water quality. Table 2 shows the general trends that were observed when comparing
water quality data for the recycle stream to that of the raw lake water and combined influent.
Table 2
General concentration trends for recycle, raw, and influent water
Parameter
Typical relative concentration
Recycle conc. < or > Recycle conc. < or >
raw lake water WTP influent water
Flow rate, daily average
---
< (-0 —10%, avg. 5%)
Turbidity (NM
<
<
TOC (mg/L)
<
<
Manganese (mg/L)
>
= or >
Iron (mg/L)
>
>
Total coliform (coliform/100 mL)
< (occasionally =)
<, _, or >
HPC (cfu/mL)
>
> or =
TSS (mg/L)
<
<
28

There are several positive aspects of the E.M. Johnson water treatment plant's recycling
system that help provide for no observable adverse impact from the recycling on finished water
quality. First, the physical system is well -designed and relatively extensive. The two primary
waste streams are treated with clarification - the primary clarifier blowdown with three sludge
thickening tanks, and the spent filter backwash water with two settling basins. Also, supernatant
from the thickeners is routed to the SFBW clarifiers. The only waste stream recycled toward the
head of the plant is the supernatant from the two backwash water settling basins. In addition,
that recycled flow does not go directly to the head of the plant, but instead is directed to the West
raw water reservoir, where it is combined with the raw lake water to form the plant combined
influent. Furthermore, the inlet for the recycled water into the reservoir is located fairly near the
raw lake water inlet, and a good distance from the outlet of the reservoir that carries water to the
head of the WTP, and thus there is a reasonable level of mixing between the recycle water and
raw water before it is used by the WTP.
Secondly, WTP personnel appear to do an excellent job monitoring performance of the
various residual and recycle treatment units and responding to changes in water quality as needed.
This conclusion is based on observations made during an in -person site visit by EE&T water
treatment engineers to the WTP in June 2007, and in numerous subsequent contacts between
EE&T and WTP personnel.
Lastly, in summer 2007 (subsequent to the period of the data analyzed in this report), three
significant improvements were made to the recycle system at the WTP. First, a UV disinfection
treatment system was installed for the backwash water settling basin supernatant to help reduce or
eliminate the viability of bacteria, Cryptosporidium, Giardia, and other pathogenic
microorganisms. UV disinfection is well above what would be considered standard treatment for
filter backwash water, and in fact EE&T knows of no other U.S. water supplier currently using
UV disinfection for this purpose. UV used in this fashion can be an excellent barrier to viruses,
Giardia, and Cryptosporidium depending upon the delivered dose. The City is going to be an
active participant in an Awwa Research Foundation research project. with EE&T to further
evaluate the delivered dose and the disinfection capability of the system. The installation of the
system and the commitment to participate in the research project exemplify the interest that the
M

City has shown in providing state of the art facilities that go well beyond requirements to treat
recycle streams.
Secondly, in summer 2007 a new recycle pump station (three 8-mgd pumps) was
constructed that now directs the backwash water settling basin supernatant (after UV disinfection)
to both the East and West raw water reservoirs. While the new pumping arrangement won't
necessarily result in additional dilution of the recycle water with the raw lake water (since water
from the two reservoirs is combined anyway prior to entering the WTP), it does provide
sufficient pumping capacity such that during periods of relatively high flow all of the filter
backwash settling basin supernatant can be pumped to the raw water reservoirs (that was not
always the case previously, as in August 2006 the flow of supernatant was too high for the old
pumps to handle and the supernatant was discharged to the nearby unnamed tributary of
Honeycutt Creek for two weeks). Lastly, piping and valve improvements were made to ensure
all of the drying bed underdrain water is directed to the sewer system (previously that water was
supposedly directed to the splitter box before the three thickeners, but a leaking valve allowed
some of that water to be directed to the SFBW settling basins instead). This improvement is
expected to result in lower manganese levels in the settling basin supernatant.
30

RECYCLING REQUIREMENTS
The E.M. Johnson water treatment plant is required by the North Carolina Department of
Environment and Natural Resources to discontinue recycling for one 2-week period each
calendar year (NCDENR 2005), and during that time to discharge the backwash water settling
basin supernatant to a nearby stream in accordance with an NPDES permit (National Pollutant
Discharge Elimination System permit). The stated purpose of this requirement is to allow
complete flushing of the raw water reservoirs and treatment plant (NCDENR 2005).
The above detailed assessment evaluated two such periods of no recycle, in June and
August 2006. The extensive water quality data evaluated showed no observable adverse impact
on finished water quality at any time for any of the water quality parameters evaluated. In
addition, the exceptional physical system design and operational practices employed by WTP
staff help to ensure no adverse impact will be realized during times other than that examined in
this report. Furthermore, the City of Raleigh has made improvements to their treatment system
after the period of data collection analyzed in this report, including installing a UV disinfection
system for the recycle water. UV disinfection is well above what would be considered standard
treatment for filter backwash water, and in fact EE&T knows of no other U.S. water supplier
currently using UV disinfection for this purpose. UV used in this fashion can be an excellent
barrier to viruses, Giardia, and Cryptosporidium depending upon the delivered dose.
As a result of the above analysis, it is our professional opinion that the NCDENR
requirement for not recycling for two weeks per year is unnecessary and unduly burdensome. In
fact, many parameters are lower in the recycle than the raw water and thus improve the plant
intake levels. The requirement puts a physical and water quality load on the receiving stream
(normally dry except for storm events) with no recognizable benefit to the WTP, and can lead to
unnecessary objections from local residents who are not familiar with the specific quality of the
discharged water nor the reasons for its discharge.
31

RECOMMENDATIONS
Based on the above analysis, it is apparent that the recycle system is well -designed and
well -operated. Nonetheless, certain improvements could be made to improve recycle water
quality, and additional study performed to further understand some of the key issues.
Accordingly, we offer the following recommendations:
1. Issue: When the main WTP sedimentation basins are cleaned out (such as in Dec.
2006 through Feb. 2007), the wash water is currently routed to the SFBW
clarifiers. This arrangement results in substantial fluctuations of recycle water
turbidity levels during the times of basin cleanout, and levels that are often higher
than the raw lake water turbidity. There would be much less impact from this
wash water if it was instead directed to the splitter box leading into the three
thickeners. That way the wash water would be treated with polymer and
clarification prior to that supernatant entering the SFBW clarifiers.
Recommendation: Install appropriate piping and valves to route the wash water
from the five main WTP sedimentation basins to the splitter box entering the
thickeners, and discontinue the current practice of routing that wash water directly
to the SFBW clarifiers. Draining of the clear water in the basins should still be
directed to the SFBW settling basins, and the wash water used for cleaning out the
solids could be directed to the thickeners. Currently finished water is used to
wash the main WTP sedimentation basins, and WTP staff are concerned that the
relatively high alkalinity in the finished water would affect the settling in the
thickeners if it was directed to them. Accordingly, if the wash water is directed to
the thickeners, the effect of using finished water on thickener settling should be
evaluated, and if there is an adverse impact then settled water should be used for
this washing (a means of storing and pumping the settled water may be
necessary). Further analysis of the potential ramifications of this recommendation
should be performed to assess all potential issues.
32

2. Issue: An improved mass balance analysis would be useful to better understand
the fate of manganese in the WTP. Also, manganese levels in the SFBW settling
basin supernatant (recycle water) were historically as high during periods when
permanganate was not used as they were when it was being applied, and it would
be good to determine the source of that manganese. Until piping improvements
were made in May 2007, some of the underdrain water from the filter cake drying
beds (which is high in manganese) was inadvertently pumped to the SFBW
settling basins. Permanganate has been used continuously since that time, so it is
as yet unknown if the piping improvements will help reduce recycle water
manganese levels.
Recommendation: Measure the manganese concentration of the thickener
overflow and the SFBW (during both periods of permanganate use and non-use),
and perform a mass balance analysis. Also, when permanganate use is next
discontinued, increase the frequency of analysis of manganese in the SFBW
supernatant to daily to better assess any improvement in manganese levels
(currently weekly analyses are performed)..
3. Issue: No TTHM or HAA5 data are available for the recycle water; only finished
water TTHM and HAA5 data are available. The highest DBP results of the year
were obtained during the warmest month (83.4 µg/L for TTHM and 66.7 µg/L for
HAA5 on August 7, 2006), about half way through a two -week period of no
recycle. Since these numbers are at least approaching the future LRAA MCL, it
would be good to determine if recycle is contributing to the levels. Recycle can
add to both the instantaneous DBP levels by recycling preformed DBPs and add
to the formation potential by adding precursors.
Recommendation: Obtain TTHM and HAA5 data for the recycle stream during
the warmest months (July and August, when DBP levels are expected to be
highest) at the same time as the monthly DBP sampling of the finished water.
Analyze for both instantaneous DBPs and SDS levels by adding additional
33

chlorine, buffering the pH to the distribution system level, and holding for an
appropriate time (— 3 days).
4. Issue: The City is currently required by the NCDENR to discharge the SFBW
settling basin supernatant (recycle water) to a nearby unnamed tributary of
Honeycutt Creek for one 2-week period each year. The above analysis showed
that this requirement is unnecessary and unduly burdensome. In fact, many
parameters are lower in the recycle than the raw water and thus improve the plant
intake levels. The requirement puts a physical and water quality load on the
receiving stream (normally dry except for storm events) with no recognizable
benefit to the WTP, and can lead to unnecessary objections from local residents
who are not familiar with the specific quality of the discharged water nor the
reasons for its discharge.
Recommendation: The City should negotiate with the State to rescind the
requirement for occasional discharge of SFBW settling basin supernatant to the
nearby creek. The NPDES permit that allows that discharge should be
maintained, however, in the event of some unforeseen circumstance where
operational conditions mandate a release of SFBW settling basin supernatant to
the creek.
5. Issue: The City has resisted using a polymer in the SFBW settling basins to
improve coagulation and clarification because of toxicity concerns from the
polymer for occasions when the supernatant is discharged to the nearby creek, as
required for one 2-week period per year by the NCDENR. The City previously
determined in 2005 that the polymer used for the splitter (entering the three
thickeners) and the filter presses was likely causing toxicity in the water
discharged to the creek. Subsequent modifications to the residuals system now
direct the press filtrate to the sewer, and no polymer is recycled from the presses.
Any polymer left over in the thickener supernatant passes along to the SFBW
settling basins.
34

Recommendation: Consider evaluating the use of a polymer to improve
clarification in the SFBW settling basins and the quality of the supernatant water
recycled. Polymer addition might be particularly helpful during the times when
wash water from cleaning out the five main WTP sedimentation basins is directed
to the SFBW settling basins (note that Recommendation No. 1 above suggests
directing that wash water to the thickeners). Since the SFBW settling basin
supernatant might on occasion need to be discharged to the nearby creek (e.g., as
was done when there was a problem with the pump station at the UV disinfection
facility in July 2007), the issue of potential toxicity of the supernatant water
containing polymer should be reevaluated. This evaluation should also include an
assessment of any impacts from recycling polymer to the raw water reservoirs.
6. Issue: Recycle water turbidity levels on occasion were measured higher than the
raw water turbidity. However, the recycle flow averages only 5.0 percent of the
influent flow (maximum of 10.0 percent), and as such on those occasions
contributes a minor increase in turbidity for the influent water compared to that in
the raw water. Overall through the one-year period studied, there were 337 days
when recycle was occurring, and of those 337 days there were 43 occasions (12.5
percent) where the -recycle water turbidity level exceeded that measured for the
raw water. Furthermore, of the times when recycle turbidity was greater than for
raw water, recycle turbidity was > 4 NTU on only 13 occasions (3.6 percent of all
sample days), and only 23 occasions where recycle turbidity was > 3 NTU (6.8
percent of all sample days). Raw water turbidity averaged 5.5 NTU during the
year. The NCDENR has stipulated a maximum turbidity for the recycle water of
30 NTU (NCDENR 2005).
Recommendation: One goal would be to establish a recycle water turbidity
maximum value, such as 4.0 or 5.0 NTU. Alternatively, the maximum could be
set at the influent turbidity, but this is a harder operating goal to monitor and
maintain and during times of low influent turbidity could be difficult to achieve.
35

REFERENCES
Cornwell, David A. 2006. Water Treatment Residuals Engineering. AWWA Research
Foundation. Denver, CO, 364 pp.
Cornwell, David A., Michael J. MacPhee, and Rodney J. Mutter. Undated. Self Assessment of
Recycle Practices. Prepared for the American Water Works Association, Government
Affairs Office. EE&T, Inc., Newport News, VA, 121 pp.
North Carolina Department of Environment and Natural Resources. January 21, 2005. Letter
from J. Wayne Munden (NCDENR) to Russell Allen (City of Raleigh).
US Environmental Protection Agency. 2002. Implementation Guidelines for the Filter Backwash
Recycling Rule (FBRR). Office of Water. EPA 816-D-01-001.
36

. Raw lake water o Influent to WTP ♦ Finished water X Recycle water
80
E 40
3
0
FL
20
r�
L-41, .s:, :a►tirr�tYr1 `''' .,tiYfiila..v..;.
W
CO
4�1
CJ)
0)
CO
CO
1
N
W
W
W
N
N
N
N
CD
N
N
N
0')
C7
O
O
O
O
CO
C)
CO
CO
CO
O
\
O
tV
N
N
C\
O
P
O
O)
CA
m
C')
CA
m
m
C)
CO
C)
�I
v
m
CA
m
Figure 2 Flow rates (Mar 2006 — Feb 2007)
37

■ % recycle of total treated water x Recycle water flow
10
.-, 8
ENo
0 6SON
M ME
Ip No
...
%
o,
4
m
AM
L01
a ME No
0 Lj
M � 00 N
W W W N N N N N N N
_O Co (0 W N N N C_31 P
a) 0 00 0 0 00 a.. a- C) o
0 0 0 CD a) a) a� C) C) CD -4 -A
Periods of no
■
■ recycle
■ ■
Figure 3 Recycle flow rate (Mar 2006 — Feb 2007)
38

■ Raw lake
50
.N
D
z 30
w
20
10
9 Influent to WTP ♦ Finished water ® Settled x Recycle
I
W
W
4�1
Cn
O)
�I
Oo
CO
1
N
W
W
W
N
N
N
N
O
N
N
N
O
O
O
O
O
C\O
O
C\O
O
CO
O
�
O
N
N
N
C\
O
?
O
O
m
O
0)
O
m
O)
O
O
O
�1
�l
O
m
m
Figure 4 Turbidity (Mar 2006 — Feb 2007)
39

■ Raw lake • Influent to WTP
100
♦ Finished water ® Settled * Recycle
Y
, 1. �
t ,
f-� � � �� ` •�. r ' , ':
� ti
'`{S♦ ��
♦: J -
11�` 1 � ;may
off YµS '4WL_Cki
r
m
W
4�h,
CP
O
v
CO
O
N
W
W
W
N
N
N
N
O
N
N
N
O
O
C\O
CD
CO
-4
N
N
N
(CJ7
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
�1
­4
O
O
O
Figure 5 Turbidity: log -scale plot (Mar 2006 — Feb 2007)
,o

■ Raw lake water X Recycle water
20
15
H
Z
' 10
L
5�
W W 4� Cr m Cfl N
O O CEO C`O Co -4 N N N C�31
m O O O O O O O O O
(A (A CA W W O O O O
m C) m
r '
Figure 6 Raw lake water and recycle water turbidity (Mar 2006 — Feb 2007)
41

■ Raw lake i Influent to WTP ♦ Finished water ® Settled x Recycle water
50
recy
40
z 30
a
20
H
10
0 y y
V! \ ` \ \
UI O P CO c\O W 00
O O O O O O O O
m m m m 0') m 0') 0")
Figure 7 Turbidity (May — Aug 2006)
42

♦ Finished water ® Settled water
1.0
Periods of no recycle
0.9
�
0.8
0.7
0.6
z
0.5
.
H-
0.4
®®
A.'
0.3
4L
♦♦
♦
♦�
A4
AL ♦
I�w
�4
0.1AAA
A
0.0
can con
-C4
a� a� -4
N
o0 Co
N N
C_n O
0)
P Co P
( W Co
0
m m m
0) � 0)
Figure 8 Settled and finished water turbidity (May — Aug 2006)
43

■ Raw lake • Influent to WTP ♦ Finished water
20
increase in ferric sulfate (Dec. 10 - 14)
16
4
X
Settled X Recycle
1
■•� X)KI
T WW
E'm
0
�
�
N
C)
O
O
O
O
O
�I
O
O
Figure 9 Turbidity during Nov. and Dec. 2006
M,

is
+
w
.
r +
,
• • • • • • •
Note: no settled water turbidity data were available for before July 1, 2006
Figure 10 Recycle, settled, and finished water turbidity (Mar 2006 — Feb 2007)
45

12
in
8
J
E 6
O
i-
4-
2-
■ Raw lake ® Influent to WTP ♦ Finished water . Settled x Recycle
�F
T
� �
�.. i
r
FAA
I
712
W
m
W
C\3lm
`
CO
CD
W
\
W
W
N
N
N
N
O
\
\
N
\
O
O
(D
(0
CO
N
N
N
O
O
O
O
O
O
\
O
O
O
O
O
O
O
O
O
O
O
O
O
O
Figure 11 TOC concentrations (Mar 2006 —Feb 2007)
m
i
I 1
U
O O
V v

i
80
Periods of
Fi�n ferri
3
�.
c sulfate
no recycle �
(45% removal is required)
♦ % TOC removal
11 VA
Figure 12 Percent TOC removal (Mar 2006 - Feb 2007)
Figure 12 Percent TOC removal (Mar 2006 - Feb 2007)

■ Raw lake water • Influent to WTP ♦ Finished water )K Recycled water)
10-
Periods of
no recycle
Figure 13 TOC concentrations (May - Aug, 2006)

■ Raw lake water a Influent to WTP ♦ Finished water ♦ Settled water
12
10
E 6-
L)
0
4
«♦<♦!�� s♦♦�♦,�♦♦♦s�•�i �+11►� m r�eoys♦�♦..wt.♦i�.<.♦1��►<u♦ ,<♦�<��.
2
0
0 \
I Q C:) C
Figure 14 Settled water TOC concentrations (Jan — Mar 2007)
49

-y
1•
♦
\
♦ I�
0
i
6
/
1
♦
♦
Figure 15 Manganese concentrations (Mar 2006 — Feb 2007)
50

o Raw lake water
♦ Finished water
0.35
, Periods of,.,--,
Period of no MnO4used
0.30
0.25
J
0.20
r
0.15
ea
00
0.10
0.05vt
0.00
MIX
=
W ((0
O �
ONO y N
N N CN31
0) o 0 0
0 0
0 0
o 0
a� (3) 01)
a) a)
a) a) O
O o -4 -4
4+
.
•
Figure 16 Finished and raw lake water manganese concentrations (Mar 2006 — Feb 2007)
51

■ Influent turbidity • Influent Mn ♦ Mn dose added
100
J
Periods of
Period of
Figure 17 Influent manganese compared to applied dose and influent turbidity (Mar 2006 — Feb 2007)
52

2.0
m
Raw lake water Influent to WTP )K Recycle water
cn w
w
rn rn rn o 0
rn rn
Figure 18 Manganese concentrations during the period of no permanganate addition (July 5 — Nov 12, 2006)
53

54
■ Raw lake water • Influent to WTP ♦ Finished water )K Recycle water
2.0
1.6
J
al
F 1.2
OW X
d
C
0.8
c
0.4
0.0i "
01 � rn rn OD 00
—W N N N
CTI O A C\O -P c\O W o7
O O O O O O O O
m 6) m O) 6) m a7 6)
Periods of
•
no recycle
zil
•
�
•
• • no Mn04
•
�
•
, used
•
Figure 19 Manganese concentrations (May — Aug 2006)

■ Raw lake water A Finished water
0.15
o.10
E
y
ai
C
m
0.05
0.00
w
rn m
m
0)
0)
0)
Mn04 used
only through
Periods of
no recycle
�
■
7/4/06
■
■
no Mn04
used
■
■
■
■
♦
III Y1i►11►
♦RMO M► W►
♦ Y
Figure 20 Manganese concentrations for raw lake water and finished water (May — Aug 2006)
55

500
!SIT
ca
.a
Y
300
N
d
C
R
200
E
fC
w
100
is
o Lake + Recycle x Mn added ♦ Influent to WTP
W
W
P
Cn
CA
�I
CO
CO
N
O
W
\
O
W
O
O
W
O
O
N
COE
O
N
C`O
O
N
Oo
O
N
\
O
O
N
N
N
N
N
CCnn
O
N
O
O
CA
CA
CA
M
CA
C)
O
O
O
-4
M
M
CA
Figure 21 Source of manganese over time (Mar 2006 - Feb 2007)
56

■ Raw lake water
)K Recycle water
75
60 -
�a
a�
Y
y
N
45
N
C
R
30
E
�a
'
15
0
W W
W
4�h-
W
M
W
CA
N
v
N
Cb
N
CD
N
O
1 N
_, N
N N
0') O
O
O
O
O
CO
O
CEO
O
00
O
�
O
N
IliN CCTI \P
O O
M
CA
CA
CA
CA
O
O
CA
O O �I v
CA CA
Figure 22 Manganese mass loadings for raw lake water vs. recycle water (Mar 2006 - Feb 2007)
57

■ Raw lake water
1000
as 100
X
y
fn
E
°'
10
to
C
!0
is
C
R
E
1
0
H
0.1
• Influent to WTP
Recycle water
Period of •
recycle
go-
/
00
cc
c\n
4�
w
O
O
O
W
N
M
CD
CD
CD
Figure 23 Manganese mass loadings during the period of no permanganate addition (July 5 — Nov 12, 2006)
58

m
3-
J
G1
E 2
C
O
=
■ Raw lake water ® Influent to WTP ♦ Finished water X Recycle water
-- •• •
0
.. 1
Lv
AI
W
CT
O
�
00
(fl
N
\
CA)W
\
\
CA)
\
N
\
NJ
\
N
\
N.)\
O
_,
\
N
\
\
N
\
N
O
O
(.0
(D
00
\
N
N
N
C\
O
O
O
O
O
O
C)
O
O
O
CA
CA
CA
O
O
CA
C)
v
v
CD
C)
Figure 24 Iron concentrations (Mar 2006 — Feb 2007)
59

125
♦ Ferric sulfate dose •
�
Periods of �
no recycle' •
•
RIC
Figure 25 Applied dose of ferric sulfate (Mar 2006 — Feb 2007)
Figure 25 Applied dose of ferric sulfate (Mar 2006 — Feb 2007)

0.20
0.15
J
E
0.10
0
L
0.05
0.00
O OO
00
=
a�
o 0 0
0 00
0
rn m a)
m a) a)
a)
a �
CD C)
♦ Finished water
Periods of
no recycle
�u
AL
ern •
�� ��■rrrn
Figure 26 Finished water iron concentrations (Mar 2006 — Feb 2007)
��

19111
2.5
2.0
a�
E 1.5
c
0
L
1.0
0.5
,1 e
■ Raw lake water • Influent to WTP ♦ Finished water )KRecycle water
•
,
;•;A� R
1 ;��
is �!7� i
,.;4�
. r
Ull
\l
6)
`
Col
CD
CEO
CD
CD
CD
m
0)
m
Figure 27 Iron concentrations (May— Aug 2006)
I
I
�
OD
00
N
N
W
00
m
�
m

■ Raw lake water • Influent to WTP
100000
J
0 10000
I �
T
N
>_
0 1000
O
U
E 100
O
0
U
w
10
0
Recycle water
OO O CEO Q 00 z N N N Q
O O O O O O O O O
O) d) O O O) O) O) C) W CD v V
Note: any data values with a "> x" designation were translated to "= x" for plotting purposes
Figure 28 Total coliform (Mar 2006 — Feb 2007)
63

■ Raw lake water • Influent to WTP ♦ Finished water * Recycle water
10000
* *)% X * MONNOM * * W A *WWA
* *
*• * •• OK ■
1000 * * �
• �� X ` *
��IKM IN
s ■ l 't�
a NIN~en X Periods of
° * ■ m L no recycle
10 a ** ■ ■ _.- cK
♦ ♦ AL 1♦
1
W W W N N N N
O O CO CO 00 �1
0) O O O O O O O
0) m CT) CY) CD 0') 0')
Note: values designated as < 20 are plotted as = 10; values designated as < 2 are plotted as = 1; and values designated as
> x are plotted as = x
Figure 29 Heterotrophic plate count (Mar — Sept 2006)
m

.-.
J
E
16
12
■ Raw lake water a Influent to WTP
♦ Finished water
)K Recycle water
...
0
Ca
8
c
a�
CO
0
0
w w gyp.
W W
can
W
a�
N
�
N
oo
N
�
N
O = O
O
seCO
OD0)
0)
Periods of no recycle (no
TSS data were availablefor these times)
SIC �K SIC SIC SIC SIC SIC ®
SIC 3�E ®
l�C 3�E �C �C SIC
♦ ♦ ■ SIC �K SIC
■ ■
�
Figure 30 Total suspended solids (Mar — Sept 2006)
65 _

f
100
♦ THM - Finished water
o HAA5 - Finished water
Peri
ods of
no recycle
�
0
oo e
a o
Figure 31 Finished water TTHM and HAA5 (Mar 2006 — Feb 2007)
Figure 31 Finished water TTHM and HAA5 (Mar 2006 — Feb 2007)

• TOC:TTHM ❑ TOC: HAA5
100
...
J
.M
80
L.
3
60
sE
40
L
0
20
s
0
2.0
2.5 3.0 3.5
Total organic carbon in finished water (mg1L)
•
D
•
❑
a
Figure 32 Finished water TTHM and HAA5 versus finished water TOC (Mar 2006 - Feb 2007)
67

V
♦ TOC:TTHM ❑ TOC: HAA5
100
,-.
80
L
•a+
3
=
60
y
ME
4=
❑ ♦ ❑
.�
40
LO
LM
C
20
0
2
4 6 8 10
Total organic carbon in influent water (mg/L)
Figure 33 Finished water TTHM and HAA5 versus influent water TOC (Mar 2006 - Feb 2007)

Assessment of Raleigh's Residuals Treatment Systems
Submitted to
City of Raleigh
Raleigh, North Carolina
Submitted by
EE&T, Inc.
712 Gum Rock Court
Newport News, VA 23606
December 2007

LIST OF TABLES ................................... ...
LIST OF FIGURES ........................... iii
.............................................................................................................
EXECUTIVESUMMARY........................................................................................................................... iv
OBJECTIVESAND APPROACH.............................................................................................................. 1
RESIDUALS AND RECYCLE SYSTEMS........................................................................................... 1
RESULTSAND DISCUSSION................................................................................................................
5
TotalSolids Produced.....................................................................................................................
5
SFWBSettling Basins...................................................................................................................
10
ThickenerOperations.....................................................................................................................
12
SludgeHolding Tanks......................................................................................................................
15
FilterPress Operations..................................................................................................................
16
FilterCake Handling......................................................................................................................
18
RECOMMENDATIONS............................................................................................................................ 19
REFERENCES.............................................................................................................................................. 20
ii

0
LIST OF TABLES
1 WTP waste stream treatment........................................................................................................ 10
2 Filter press solids information..................................................................................................... 17
3 Filter press hydraulic and solids loading rates.......................................................................... 18
LIST OF FIGURES
1 Schematic of recycle/residuals system (as of September 2007)........................................... 3
2 Calculated solids production based on plant operations data (March 2006 to
April2007)............................................................................................................ 7
3 Comparison of calculated solids production to observed solids in filter press feed
(2006 data)............................................................................................................ 8
4 Comparison of reported cake removal to calculated and observed solids production
(2006 data)............................................................................................................ 9
5 Cumulative distribution of calculated SFBW settling basin HLRs from March 2006
toApril 2007......................................................................................................... 11
6 Cumulative distribution of calculated thickener HLRs from March 2006 to April
2007...................................................................................................................... 13
7 Cumulative distribution of thickener SLRs from March 2006 to April 2007.................. 14
iii

EXECUTIVE SUMMARY
OBJECTIVES AND APPROACH
This memorandum provides an evaluation of the residuals treatment systems employed at
the E.M. Johnson water treatment plant (WTP) and recommendations designed to help improve
performance and reduce operating costs. This assessment is based on data provided by the City
of Raleigh Public Utilities Department, including information on the production of solids as well
as operation of the spent filter backwash water (SFBW) settling basins, gravity thickeners,
sludge holding tanks, belt filter presses, and filter cake handling facilities. Data from other water
treatment plant operations were also used such as flow, turbidity, and total suspended solids
(TSS). Operational factors such as hydraulic loading rate (HLR) and solids loading rate (SLR)
were evaluated for the gravity thickeners and filter presses. HLR was also evaluated for the
SFBW settling basins, and a separate detailed evaluation of potential water quality impacts from
recycling SFBW setting basin supernatant was also performed (EE&T 2007).
SUMMARY OF RESULTS AND DISCUSSION
Solids Production
Calculations of the amount of solids produced by the WTP were calculated in three ways:
(1) using influent water quality data and treatment chemical dosages; (2) data for the solids
coming from the holding tanks to the filter presses; and (3) reports of the amount of solids hauled
away as compost. Since there was not a good correlation between any of these three results, it is
recommended that a study be conducted to collect additional information to better characterize
solids production at the treatment plant, especially as it relates to the values the City is being
charged to haul.
iv

SFWB Settling Basins
Currently, no equalization storage is provided to dampen peak flows during filter
backwashes. Furthermore, the instantaneous HLRs are higher than would normally be
recommended for SFBW settling basins that do not use polymer. Nonetheless, as shown in the
separate report for the recycle system analysis (EE&T 2007) there is currently no observable
impact on water quality from recycling the SFBW settling basin supernatant, which indicates that
the SFBW settling basins are performing adequately.
Gravity Thickeners
In general, the calculated solid loading rates (SLRs) with three thickeners in service are
within the normally observed range, although at the higher end of the range (typical range 0.1 to
0.4 lb/hr-ft ). With one thickener out of service, the thickener SLRs exceed what would be
considered normal operating range at other water treatment plants. The thickener hydraulic
loading rates (HLRs) are also within the range normally observed at other water treatment plants
when all three thickeners are in service. With one of the thickeners out of service, occasionally
the thickener HLRs may exceed the high end of the normally observed range. Based on both the
SLR and HLR results, it is recommended that a fourth thickener be added so that the plant can
keep three thickeners in service at all times, even when one thickener is out of service for
maintenance.
Sludge Holding Tanks
Available data show that the available storage time is, approximately 1.0 days for the
median flow rate of sludge to the filter presses, and 0.6 days for the upper 90th percentile flow
rate. While these storage times are relatively short, they should be sufficient to maintain normal
operation of the filter presses (23 hours of operation per day with 1 hour of down time for
maintenance). If additional operational flexibility is desired, the addition of a fifth storage tank
will provide an additional 6 hours of sludge storage during median conditions, which may be
v

o,
helpful if the filter presses cannot be operated due to maintenance. It would be appropriate to
install sludge level gauges in each tank, as well as a means to automatically transmit that data to
the dewatering system building to aid in operator evaluation.
Filter Press Operations
The median and maximum (90th percentile) HLR were calculated as 32 and 56
gpm/meter, respectively, and the median and maximum SLR were calculated as 321 and 521
lbs/hour/meter,• respectively, based on operating one filter press 23 hours per day. During
maximum conditions two (or even three) filter presses are operating, which would cut in half
these maximum HLR and SLR values. In general, the calculated median HLRs and SLRs are
within the range of values that are typically observed at comparable plants, however, the
maximum values for SLR are above typical values if only one press is operating. The City
should consider operating two presses during these higher conditions, if it does not already do so.
It was separately recommended the City consider whether the existing presses or with the
addition of a fourth press the sludge material in the reservoirs could be dewatered by the city to
avoid contractor dredge and dewatering costs.
Filter Cake Handling
The current system for filter press cake handling requires the cake be handled twice —
once to move it to the storage area, and once again to load it onto the 20 cubic yard trailers used
by the hauler. Also, there is no cover over the outdoor filter press solids drying bed. Since the
solids are hauled away as compost and this is paid for by the City on a weight basis, any rain
water in the solids is also paid to be trucked away. Unfortunately, as noted above neither the
calculated solids production nor the observed solids feed to the filter presses correlates well with
the reported values that the cake hauler is charging the plant for transportation. Furthermore,
there is no clear bias in the discrepancy; the calculated and observed values are neither
consistently higher nor consistently lower than the reported values. For this reason, additional
studies are recommended to assess the accuracy of the values that are reported by the cake
vi

a
hauler. Regardless of that result, the City should consider evaluating different options for
keeping the filter press solids covered, as well as installation of an on -site truck scale to weigh
the amount of cake hauled away.
RECOMMENDATIONS
The recommendations proffered based on this assessment are summarized as follows:
1. Initiate a study to better determine discrepancies between calculated, plant
measured, and hauler reported solids quantities.
2. Consider installation of a fourth thickener to provide additional capacity, and to
enable three thickeners to be operating while one is being cleaned and/or serviced
3. Consider installation of a fifth sludge holding tank prior to the filter belt presses to
provide additional capacity, including more storage time if the filter press
operation is temporarily unavailable
4. It would be appropriate to install sludge level gauges in each tank, as well as a
means to automatically transmit that data to the dewatering system building to aid
in operator evaluation
5. Consider the feasibility of using the existing processes or additional presses to
process sludge from the on -site lagoons as an alternative to hiring a contractor to
dredge and dewater the material.
6. The City should consider evaluating different options for keeping the filter press
solids covered. Possibilities include (a) constructing a roof over the current
drying bed, and (by devising a system where several trailers are kept on site,
loaded one at a time directly from the filter press conveyor belt, and then covered
with a tarp until a time when it is convenient for them to be hauled away. This
latter method would require changes to the filter press building structure to
accommodate the 20 cubic yard trailers used by the hauler, but would also
eliminate the need to handle the cake twice. Either of these methods (`a' or `b')
should save on shipping costs (due to a lower weight of the solids). The City
vii

could also explore the possibility of getting the filter cake classified as "Class A",
and then perhaps the local wastewater plant would be able to take the WTP filter
cake and mix it with theirs.
7. Consider installation of an on -site truck scale to weigh the amount of cake hauled
away
viii

ASSESSMENT OF RALEIGH'S RESIDUALS TREATMENT SYSTEMS
CITY OF RALEIGH, NORTH CAROLINA
OBJECTIVES AND APPROACH
This memorandum provides an evaluation of the residuals treatment systems employed at
the E.M. Johnson water treatment plant (WTP). This assessment is based on data provided by
the City of Raleigh Public Utilities Department, including information on the operation of the
spent filter backwash water (SFBW) settling basins, gravity thickeners, sludge holding tanks, and
belt filter presses. Data from other water treatment plant operations were also used such as flow,
turbidity, and total suspended solids (TSS). Operational factors such as hydraulic loading rate
(HLR) and solids loading rate (SLR) were evaluated for the gravity thickeners and filter presses.
HLR was also evaluated for the SFBW settling basins, and a separate detailed evaluation of
potential water quality impacts from recycling SFBW setting basin supernatant was also
performed (EE&T 2007).
RESIDUALS AND RECYCLE SYSTEMS
The City of Raleigh's E.M. Johnson water treatment plant (WTP) is rated for a capacity
of 86 mgd in April through October, and 78 mgd for November through March. The amount of
water treated averaged 52.5 mgd for the one-year period from March 2006 - February 2007 (the
period of study for the separate recycle evaluation (EE&T 2007)). The plant uses ozonation for
primary disinfection (to help meet disinfection by-product (DBP) regulations), ferric sulfate
coagulation and clarification (five sedimentation basins), high -rate sand filtration (22 filters; up
to 5.5 gpm/ft), and chloramination for residual disinfection. In the month of March chlorine is
used instead of chloramines. Powdered activated carbon (PAC) is also occasionally used. Raw
water is obtained from Falls Lake.
Raw lake water and recycled water (supernatant from the spent filter backwash water
(SFBW) settling basins) are combined in each of two raw water reservoirs (the East and West
Reservoirs), both with a rated capacity of approximately 70 million gallons. With an average
WTP influent flow of 52.5 mgd (combined from both reservoirs), each reservoir provides
1

approximately 2.7 days of detention time. Potassium permanganate or sodium permanganate is
added to the raw water lines before the two raw water reservoirs for oxidation of organics and
taste- and odor -causing compounds (and has been since the early 1990s). Permanganate is
generally not used at the same time as ozone.
A schematic of the recycle and residuals management system is provided as Figure 1.
There are two primary waste streams generated by the WTP processes: sedimentation tank
blowdown and filter backwash.
Spent filter backwash (including filter to waste) is conveyed by gravity to two filter
backwash sedimentation basins (the North and South Basins). The SFBW flow is intermittent,
up to 22 times per day if each filter is backwashed once. From March 2006 to April 2007, the
average filter backwash produced 114,000 gallons of waste. Calcium thiosulfate, used for
dechlorination, is introduced to the SFBW prior to the North and South Basins. The thiosulfate is
added in case of an operational event that leads to discharging recycle water to a nearby
unnamed tributary of Honeycutt Creek (which drains back into Falls Lake). Caustic is also
added occasionally to the SFBW before the settling basins. SFBW clarifier sludge (from the
North and South basins) is collected and pumped back to the head of the residual waste treatment
system into the three gravity thickeners, while the supernatant is pumped to the two raw water
reservoirs where it is combined with the raw lake water to form the plant combined influent.
Operation of the SFBW clarifiers is discussed in more detail further below.
The three gravity thickeners receive waste from two sources, blowdown from the five
primary WTP sedimentation tanks and sludge from the North and South SFBW settling basins.
Supernatant from the thickeners is conveyed to the SFBW settling basins, and the solids stream is
directed to four 25,000-gallon sludge blending/holding tanks prior to the belt filter press
dewatering system. Filter cake solids are stored on -site prior to being hauled away as compost,
and the press filtrate is pumped to the local sewer system. Operation of the gravity thickeners and
filter presses is discussed in more detail below.
A 26-MG on -site sludge storage lagoon is used occasionally to store solids resulting from
cleaning out the SFBW settling basins. The cleaning is done approximately once per year, but has
not yet been done since recycling started in February 2006. The solids remain in the lagoon until
dredged and hauled off -site.
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Figure 1 Schematic of recycle/residuals system (as of September 2007)
3

j
Several improvements to the WTP operations have been implemented by the City of
Raleigh in the past couple of years, including the following:
• Started recycling SFBW settling basin supernatant to the West Raw Water
Reservoir in February 2006, with intensive data collection for analyzing any
potential impacts on water quality.
• Air scouring was introduced to the filter backwash operations to reduce the
amount of SFBW produced.
• The chemical used for dechlorination was changed from sodium bisulfite to
calcium thiosulfate.
• Sludge blanket measurement instrumentation was installed in two of the three
thickeners (it was already used in one of the thickeners), and remote displays of
the measurements were installed in the dewatering system building (previously
was only displayed locally at the one thickener).
More recently, the following three improvements were made in 2007:
• On July 5, 2007 a new ultraviolet (UV) disinfection treatment system was started
up to provide a high level of disinfection for the supernatant from the SFBW
settling basins. The UV will help further remove coliform bacteria from the
recycle stream, and it is also particularly effective for sterilizing Cryptosporidium
and Giardia, depending upon the delivered dose.
• On July 5, 2007 a new pump station was installed (with three 8-mgd pumps) to
pump the treated spent filter backwash water to both the East and West raw water
reservoirs. While the new pumping arrangement won't necessarily result in
additional dilution of the recycle water with the raw lake water (since water from
the two reservoirs is combined anyway prior to entering the WTP), it does provide
sufficient pumping capacity such that during periods of relatively high flow all of
the filter backwash settling basin supernatant can be pumped to the raw water
reservoirs (that was not always the case previously; e.g., in August 2006 the flow
4

of supernatant was too high for the old pumps to handle and the supernatant was
discharged to a nearby creek for two weeks.
• Piping and valve improvements were made on May 18, 2007 to discharge the
drying bed underdrain water to the sewer system. Previously the underdrain
water was pumped to the splitter box just before the three thickeners, but a
leaking valve allowed some of that water to be directed to the SFBW settling
basins, potentially resulting in unnecessarily elevated manganese levels in the
settling basin supernatant.
RESULTS AND DISCUSSION
A discussion of the total amount of solids produced by the WTP is presented below,
followed by discussions of operation of the SFBW settling basins, gravity thickeners, sludge
storage tanks, filter presses, filter cake handling, and related facilities.
Total Solids Produced
The amount of solids reported in the filter cake was compared to the amount of solids
calculated to be produced by the water treatment plant. This was done in part to compare the
calculated amount of solids produced to that being paid to be hauled away. The mass of solids
reported in the filter cake was calculated from the mass of cake hauled away as compost (as
reported by the hauling contractor) and results from total solids tests on the filter cake (coming
off the presses and prior to outside storage). The amount of solids produced by the WTP was
calculated using the equation:
S = (8.34 x Q x (bTu + 0.805 Fe + (TOCi — TOC f )+ PAC + PolyJ)+ Poly, (1)
where S = residuals production (lb/d)
Q = plant flow (mgd)
b = ratio of total suspended solid (TSS) in mg/L to turbidity in ntu
Tu = influent flow turbidity (ntu)
Fe = ferric sulfate dose (mg/L as Fe2(SO4)3)
�1

TOC; =
influent total organic carbon (mg/L)
TOCf =
finished water total organic carbon (mg/L)
PAC =
powdered activated carbon dose (mg/L)
Poly, =
coagulant aid polymer dose (mg/L)
Polyt =
polymer added to thickeners (lb/d)
One important factor in the above equation is the TSS:turbidity ratio, which is used to
related the turbidity in the plant influent (which is frequently sampled) to the total suspended
solids in the plant influent. This factor was estimated using total suspended solids data that were
available approximately weekly for the period of March through September 2006, and the daily
turbidity data from the same period. On average, the TSS/turbidity ratio (b) was equal to 0.82
(mg/L)/ntu. This value was on the low end of the typical range for this ratio (0.7 to 2.2), and was
lower than the value of 1.5 (mg/L)/ntu which is typically used to estimate total suspended solids
when empirical data are not available. Review of the procedures used to collect the TSS data
used above showed that the sample volumes used in the TSS analyses were relatively small (200
to 500 mL), which may have skewed the TSS results since the TSS of the plant influent is so
low. Increasing the sample volume to >_ 1 L may increase the accuracy of the TSS analysis. To
illustrate the extent that this factor influences the calculated solids production, two calculated
solids productions will be presented in this report, using both the calculated TSS:ntu ratio of 0.82
(mg/L)/ntu and value of 1.5 (mg/L)/ntu (all other components in the solids production
calculations are identical).
Because solids in the finished water and SFBW supernatant are minimal, it was assumed
that all of the solids entering and generated by the WTP would end up in the filter cakes. A
summary of the plant's solids production between February 9, 2006 (the day that recycling of
spent filter backwash water started) and February 28, 2007 is plotted in Figure 2. Note that,
because the amount of polymer used in the gravity thickeners and filter presses was available
only on a monthly basis, and each month's amount of polymer was averaged throughout each
month to calculate a daily mass of solids produced.
0

100%
00 0 _ oo a
o TSS:ntu = 0.82 (mg/L)/ntu l0C�
�
3
90%
o TSS:ntu =1.5 (mg/L)Into CFF
>
80%
++
70%
N
N
60%
C
j/
.0
50%
itd
40%
.Q
O
30%
O
c
20%Af
L
IL
10%
0%
-
5,000 10,000 15,000 20,000 25,000 30,000 35,000 40,000
Solids Production (lb/day)
Figure 2 Calculated solids production based on plant operations data (March 2006 to
April 2007)
As a check, the monthly calculated solids production was compared to operating data
from the filter presses, the results of which are shown in Figure 3. The values shown as the
solids in the filter press feed were calculated by multiplying the measured flow data to the
presses by the average monthly solids concentration of that feed, which was provided by plant
staff.
As evident in Figure 3, there is no correlation between the calculated solids production
and the observed solids in the filter press feed. During some months the two values are quite
close, while during other months the values are considerably different. The reason for this
discrepancy is not immediately obvious. One explanation could be that the actual solids
concentration in the filter press feed is, on average, less than the values that were reported. This
is reasonable considering that the filter press feed may vary throughout the month, so it is
possible that average solids concentration is not captured by the one solids concentration
measured for each month.
7

1,200,000
1,000,000
800,000 ® solids in filter
a
press feed
Z
O 600,000 — —
m
a
■calculated solids
0
y production w/
400,000 — - — TSS:ntu = 0.82
D calculated solids
200,000 production w/
TSS:ntu = 1.5
0
Mar Apr May June July Aug Sept
Date
Figure 3 Comparison of calculated solids production to observed solids in filter press feed
(2006 data)
The situation becomes even less clear when calculated and observed solids production is
compared to the amount of wet solids present in the filter cake (as reported by the hauler).
Figure 4 shows this data for the period of March through September 2006 (when WTP influent
TSS data were available). Note that, in Figure 4, the solids in the fresh cake were calculated by
dividing the dry solids in the filter press feed by the solids concentration of the filter press cake.
It should be noted that the reported data from the hauler are not directly equivalent to the solids
production, as there is a variable lag time between when the filter cake is produced and when it is
hauled away, however, it is useful to compare the two to observe general trends in the data.
Please note that the values shown in Figure 4 represent the mass of the wet cake, as
opposed to the mass of dry solids shown in Figure 3. Thus, any change in cake mass due to
evaporation or absorption of precipitation on the storage pad would be represented in Figure 4.
However, the extreme differences between the reported cake mass and the other three values are
unlikely to be solely attributable to loss or gain of water. Instead, it appears that additional data
would need to be collected to adequately characterize solids production at the treatment plant.
E

2,500
2,000
e
$
1,500
— —
a
3
tl!
9
c
1,000
N
500
—
Mar Apr
May June July Aug Sept
Date
® solids in fresh
filter cake
■ calculated solids
production w/
TSS:ntu = 0.82
❑ calculated solids
production w/
TSS:ntu = 1.5
❑ reported cake
mass
IIgure 4 Comparison of reported cake removal to calculated and observed solids
production (2006 data)
In theory, the calculated solids production should be fairly accurate because it is based on
fundamental chemistry and mass balance principles, and relies on plant operations data that are
generated frequently (raw water turbidity, coagulant feed, etc.). While the TSS:ntu ratio can
vary, as discussed previously, Figures 3 and 4 show, the change in calculated solids production
that results from changing the TSS:ntu ratio is not sufficient to explain the discrepancy between
observed, calculated, and reported values; thus, this difference cannot be solely attributed to the
uncertainty regarding the TSS:ntu ratio. It is more probable that the difference is due to
problems with the measured solids concentration in the filter press feed or the weight of the filter
cake reported by the hauler, because information on these waste streams is calculated much less
frequently. It is recommended that a study be conducted to collect additional information to
better characterize solids production at the treatment plant, especially as it relates to the values
the City is being charged to haul.
9

SFBW Settling Basins
Data for the operation of the two SFBW settling basins are provided in Table 1, including
the dimensions, hydraulic loading rates, and normal chemical doses. Unless otherwise noted,
data in Table 1 was provided by WTP staff.
Table 1
WTP waste stream treatment
Treatment Unit North/South Settling Basins Thickeners
Number of units
Waste stream treated
Frequency of process influent
Fate of supernatant
Frequency of supernatant removal
Fate of solids
Frequency of solids removal
Physical dimensions:
2
SFBW (incl. filter to waste);
thickener supernatant
intermittent - up to 22 times per day
(enters via gravity)
pumped to Raw Water Reservoirs
(2 weeks/year to stream)
continuous
pumped to thickeners
intermittent - once/hr
3
clarifier blowdown; filtrate overflow from sewer pump
station (filter press/drying bed liquids)
intermittent - once/hour
(enters via gravity)
via gravity flow to North/South Settling Basins
continuous
pumped to holding/blending tanks filter presses
-► storage beds i hauled away as compost
each thickener: 300 gpm pump, set to pump
between 2 and 8 minutes/hour depending on the
level of solids in the thickener
Length (ft)
290.5
N/A
Width (ft)
62.75
N/A
Diameter (ft)
N/A
50
Side water depth (ft)
14.5
12
Surface area (fe)
18,230
1,960
Volume (Mgal)
1.383
0.202
Median hydraulic loading rate (gpm/ft)
0.291
0.08t
Max. hydraulic loading rate (gpm/fe)
0.36t
0.16t
Type of chemical used
calcium thiosulfate
polymer
Avg. dose of chemical (mg/L)
31
12.3
Frequency of chemical addition
continuous
continuous
t This value calculated from WTP operations data
Figure 5 shows a percentile plot of the distribution of instantaneous hydraulic loading
rates (HLRs) to the North and South basins. Based on plant operations data from January 2006
through February 2007, the median and 901h percentile HLRs for each of these basins are 0.29
and 0.36 gpm/ft2, respectively (or 418 and 518 gal/day/f12, respectively).
10

100%
90%
m
80%
c
,C 70%
U)
N
4) 60%
N
C
50%
cc
u) 40%
O
4-
0 30%
c
d
s- 20%
a)
IL
10%
0%
0.1 0.2 0.3 0.4 0.5 0.6
HLR (gpm/fe)
Figure 5 Cumulative distribution of calculated SFBW settling basin HLRs from March
2006 to April 2007
Currently, no equalization storage is provided to dampen peak flows during filter
backwashes. As such, during long periods throughout the day the settling basins are
underutilized as only minor flows (supernatant from the thickeners) are directed to the basins.
Equalization would help to more evenly distribute backwash flow throughout the day, more
effectively utilizing the settling basins. Furthermore, the instantaneous HLRs are higher than
would normally be recommended for SFBW settling basins that do not use polymer. However,
as shown in the separate report for the recycle system analysis (EE&T 2007) there is currently no
observable impact on water quality from recycling the SFBW settling basin supernatant, which
indicates that the SFBW settling basins are performing adequately. One possible explanation for
this is that the configuration of the settling basins (relatively long and narrow) serves to dampen
the surge of solids loading during backwash events, essentially providing equalization storage
11

inside of the basins. Regardless, the performance of the SFBW settling basins appears to be
satisfactory, so equalization does not appear to be necessary.
Solids are removed from the SFBW settling basins and directed to the gravity thickeners.
When the SFBW settling basin blowdown procedure is first started, the blowoff is fairly thick,
and then within about 20 seconds it largely clears up. For each basin, the blowdown valves are
opened for 1 to 1.5 minutes every 60 to 70 minutes. The current blowdown regime appears
adequate in removing solids from the settling basins.
Thickener Operations
Data for the operation of the three thickeners (and also the two SFBW settling basins) are
provided in Table 1, including the dimensions, hydraulic loading rates, and normal chemical
doses.
A splitter box located immediately prior to the three gravity thickeners distributes flow to
the thickeners from two sources: primary WTP sedimentation tank blowdown and SFBW
clarifier sludge (from the North and South basins). Flow from the primary sedimentation tanks is
recorded by a meter upstream of the splitter box; however, no flow meter is positioned to record
flow from the SFBW clarifier blowdown to the thickeners. While it is always useful to maintain a
record of all process flows, contribution from the SFBW clarifiers to the gravity thickeners is
minor due to the frequency (-1.5 minutes every hour) and relatively low solids concentration of
the SFBW clarifier blowdowns. For this reason, flow from the SFBW clarifiers has not been
included in the thickener loading calculations.
Thickener supernatant effluent is conveyed by gravity to the two SFBW settling basins
(North and South Basins) on a continuous basis. Thickener sludge is pumped to the sludge
holding/blending tanks and then dewatered via the belt filter presses. Polymer (Praestol
A3025L, Ashland Specialty Chemical, Greensboro, NC) is introduced at the splitter box to aid
in thickener sludge blanket formation and maintenance. As reported in the 2006 Filter
Backwash Recycling Rule (FBRR) Quarterly Reports, the polymer is added to achieve a
concentration of approximately 12.3 mg/L.
Data provided by plant staff indicated that the main process sedimentation basins
blowdown solids every 76 to 80 minutes, with a blowdown duration of 27 to 34 minutes. Thus,
12

at any time during the day, blowdown may be coming from one to four sedimentation basins into
the thickeners. Assuming the basin blowdowns are spread evenly during the day, the ratio
between peak to average flow rates from the thickeners was calculated to be 1.9 to 1.
A percentile plot of the daily peak HLRs to the thickeners is shown in Figure 6. Also
shown is what the percentile plot would be if one thickener was out of service for maintenance.
In general, with three thickeners in service, the thickener HLRs are within the range
normally observed at other water treatment plants. With one of the thickeners out of service,
occasionally the thickener HLRs may exceed the high end of the normally observed range.
100%
90%
m
80%
c
t 70%
N
N
d 60%
N
C
50%
m
40%
O
30%
c
as
v
(Dy 20%
a
10%
0%
—Three Thickeners in Service
—Two Thickeners in Service
"Typical" HLR
0.05 0.10 0.15 0.20 0.25 0.30 0.35
Hydraulic Loading Rate (gpm/fe)
Figure 6 Cumulative distribution of calculated thickener HLRs from March 2006 to April
2007
13

The inherent variability of the solids concentration in the sedimentation basin blowoff
makes it difficult to definitively calculate the solids loading rate (SLR) of the thickeners.
Information provided by plant staff indicated that the residuals coming into the splitter box are, on
average, 0.48 percent solids. Note that this is an average value; when the basin blowdown
procedure is first started the blowoff is fairly thick, and then shortly thereafter it largely clears
up. Using this information, the daily peak SLR for the thickeners was calculated and is plotted in
Figure 7.
100%
90%
d
80%
N
C
,0 50%
es
U) 40%
O
w
0 30%
C
d
c�
20%
a
10%
0% 4-
0.0
—Three Thickeners in Service
—Two Thickeners in Service
'Typical' SLR
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
Solids Loading Rate (lb/hr-fe)
Figure 7 Cumulative distribution of thickener SLRs from March 2006 to April 2007
14

In general, the calculated SLRs with three thickeners in service are within the normally
observed range, although at the higher end of the range (typical range 0.1 to 0.4 lb/hr-ft). With
one thickener out of service, the thickener SLRs exceed what would be considered normal
operating range at other plants. Based on both the HLR and SLR results, it is recommended that a
fourth thickener be added so that the plant can keep three thickeners in service at all times, even
when one thickener is out of service for maintenance. Simple pilot studies could be used to
confirm design values, although, plant operators' observations seem to confirm the need for a
fourth thickener.
Sludge Holding Tanks
Sludge from the three gravity thickeners is conveyed to the four 25,000-gallon sludge
holding tanks. Sludge from each thickener is pumped to the holding tanks for between two to
eight minutes each hour, depending on the level of solids in the thickener. The sludge is mixed
in each tank using an impeller mixer. The holding tank solids concentration ranges from 1.8 to
4.0 percent, but normally is around 2.5 percent.
The four holding tanks are interconnected with piping, and thus the level of sludge is the
same in each tank. The tanks currently do not have level gauges, and visual inspection is
required to determine the sludge level. If the level gets too high, then a level control stops the
pumps from the thickeners so that no further sludge is added to the tanks. If the tanks
inadvertently overflow, an open overflow pipe directs the excess sludge to one of the outdoor
drying beds. According to plant staff, sludge level indicators are planned to be installed in each
tank, which should ease the labor burden on the operators, and provide improved control of the
liquid storage levels.
Based on data available for filter press operations for the period of March 2006 to April
2007, the median flow rate to the filter presses was 96,500 gpd. During that same period, the
go, percentile flow rate reached 168,500 gpd. Given a 100,000 gallon sludge storage capacity,
these flow rates correspond to storage times of 1.03 and 0.59 days, respectively. While these
storage times are relatively short, they should be sufficient to maintain normal operation of the
filter presses (23 hours of operation per day with 1 hour of down time for maintenance). If
additional operational flexibility is desired, the addition of a fifth storage tank will provide an
15

additional 6 hours of sludge storage during median conditions, which may be helpful if the filter
presses cannot be operated due to maintenance.
Filter Press Operations
Final dewatering of the thickened solids is performed using three 2-meter Ashbrook belt
filter presses. Typically only one filter press is operated at a time for 23 hours a day (the other
hour is used for cleaning and maintenance). However, a second filter press is simultaneously
used as needed. Three filter presses can not be used simultaneously because that would generate
more filtrate flow than can be handled by the pump and piping that directs it to the sewer system
(i.e., the filtrate pump and piping only have enough capacity for the filtrate from two presses).
There is an overflow weir wall in the sewer pump station that directs any filtrate overflow to the
splitter box before the three thickeners, but it is an operational goal to not have any of the press
filtrate recycled in that manner.
Table 2 presents information about operation of the filter presses, including the amount
of solids processed on a monthly basis from January 2006 through February 2007. Based on
long term historical observations by treatment plant staff, the holding tank solids range from 1.8
to 4.0 percent but normally are around 2.5 percent; this waste stream is dewatered by the filter
presses to achieve an average solids concentration in the filter cake of 21.5 percent (Table 2).
Polymer is fed to the effluent from the holding tanks (entering the filter presses) to aid
in dewatering at a rate of between 3.0 gpm and 3.8 gpm depending on the level of percent
solids in the holding tanks at any particular time. The polymer used is the same (Praestol
A3025L) as that used in the gravity thickeners. The amount of polymer used that is shown in
Table 2 is that for both the filter presses and gravity thickeners combined; data for each separate
use were not available other than for a few days.
Belt filter press filtrate and spent spray wash water are pumped to the sanitary sewer
through the sewer pump station. In addition, there is a spray stream used to clean the solids
conveyor belt ("conveyor belt spray down"), and that stream is also pumped to the sanitary sewer
through the sewer pump station.
16

Table 2
Filter press solids information
2006
2007
Item Jan '06 Feb Mar Apr May June July Aug Sept Oct Nov Dec Jan '07 Feb
% solids in feed to presses *
1.96
2.16
2.05
2.15
2.39
2.48
3.49
3.41
2.41
2.29
2.21
2.43
2.66
2.70
mass of filter cake (i.e.,- dewatered
1,107
1,062
1,242
1,431
1,530
1,431
1,008
1,521
1,512
1,620
1,350
1,917
2,448
2,160
sludge) (tons) "
% solids in filter cake *
21.0
20.6
21.6
21.4
21.7
22.7
21.0
23.6
22.9
21.8
21.8
20.6
19.7
21.2
polymer used (Ibs) - for both the
6,870
5,496
6,675
6,898
6,675
6,453
7,654
11,481
6,052
6,942
8,143
10,903
11,450
14,329
thickeners and belt presses
*solids test performed on -site by WTP staff
^values for the mass of filter cake were provided by the hauler of the filter press cake solids
January 2006 through February 2007
Item Min Max Avg
% solids in feed to presses *
1.96
3.49
2.49
mass of filter cake (i.e., dewatered
1,008
2,448
1,524
sludge) (tons) ^
% solids in filter cake *
19.7
23.6
21.5
polymer used (Ibs) - for both the
5,496
14,329
8,287
thickeners and belt presses
17

Table 3
Filter press hydraulic and solids loading rates
Maximum (90th percentile)
Median conditions conditions
Hydraulic loading rate (gpm/meter) 32 56
Solids loading rate ((lbs/hour)/meter) 321 521
Note: The average and maximum HLR and SLR presented were calculated based on. typical
conditions of using only one filter press at a time. During maximum conditions two filter presses
would be used simultaneously, and as such the maximum HLR and SLR reported in this table
would be reduced by 50 percent.
Based on the available data for filter press operations, median and maximum HLR and
SLR were calculated, and are presented Table 3. These calculations are based on one filter press
operating 23 hours per day. Also, the amount of solids in the filter press filtrate was considered
negligible compared to the amount in the feed sludge and resulting cake. During maximum
conditions two (or even three) filter presses are operating, which would cut in half the maximum
HLR and SLR reported in Table 3. In general, the calculated median HLRs and SLRs are within
the range of values that are typically observed at comparable plants, however, the maximum
values for SLR are above typical values.
Filter Cake Handling
The filter press solids are stored in one of the open outdoor mud cake storage pad/drying
beds (other drying beds are currently unused), and underdrain liquid from all of the drying beds
is pumped to the sanitary sewer through the sewer pump station. The current system for filter
press cake handling requires the cake be handled twice — once to move it to the storage area, and
once again to load it onto the 20 cubic yard trailers used by the hauler. Also, there is no cover
over the outdoor filter press solids drying bed. Since the solids are hauled away as compost and
this is paid for by the City on a weight basis, any rain water in the solids is also paid to be
trucked away. Raleigh has in the past considered various alternatives for preventing
precipitation from contacting the filter press solids, and at one time estimated the cost for
constructing a roof over the drying bed.
18

Unfortunately, neither the calculated solids production nor the observed solids feed to the
filter presses correlates well with the reported values that the cake hauler is charging the plant for
transportation. Furthermore, there is no clear bias in the discrepancy; the calculated and
observed values are neither consistently higher nor consistently lower than the reported values.
For this reason, additional studies are recommended to assess the accuracy of the values that are
reported by the cake hauler.
RECOMMENDATIONS
Based on the above assessment and discussions with WTP staff, the following structural
and operational recommendations are provided:
• Consider installation of a fifth sludge holding tank prior to the filter belt presses to
provide additional capacity, including more storage time if the filter press
operation is temporarily unavailable.
• It would be appropriate to install sludge level gauges in each tank, as well as a
means to automatically transmit that data to the dewatering system building to aid
in operator evaluation
Initiate a study to better determine discrepancies between calculated, plant
measured, and hauler reported solids quantities.
• Consider the feasibility using the existing presses or an additional press to process
sludge from the on -site lagoons as an alternative to hiring a contractor to dredge
and dewater the material.
• Consider upgrades to the filtrate pumping system and/or piping to accommodate
operation of three presses simultaneously. A cost study is also recommended to
determine if a fourth filter press will enable the plant to dewater existing residuals
currently stored in the lagoon. Compare operating data to see if two presses
should be operated when the SLR exceeds about 300 lb/hr-m.
The City should consider evaluating different options for keeping the filter press
solids covered. Possibilities include (a) constructing a roof over the current
drying bed, and (b) devising a system where several trailers are kept on site,
19

loaded one at a time directly from the filter press conveyor belt, and then covered
with a tarp until a time when it is convenient for them to be hauled away. This
latter method would require changes to the filter press building structure to
accommodate the 20 cubic yard trailers used by the hauler, but would also
eliminate the need to handle the cake twice. Either of these methods (`a' or `b')
should save on shipping costs (due to a lower weight of the solids). The City
could also explore the possibility of getting the filter cake classified as "Class A",
and then perhaps the local wastewater plant would be able to take the WTP filter
cake and mix it with theirs.
• Consider installation of an on -site truck scale to weigh the amount of cake hauled
away.
REFERENCES
Cornwell, David A. 2006. Water Treatment Residuals Engineering. AWWA Research
Foundation. Denver, CO, 364 pp.
Cornwell, David A., Michael J. MacPhee, and Rodney J. Mutter. Undated. Self Assessment of
Recycle Practices. Prepared for the American Water Works Association, Government
Affairs Office. EE&T, Inc., Newport News, VA, 121 pp.
EE&T. 2007. Assessment of Raleigh's Recycle System (Draft). Environmental Engineering &
Technology, Inc. (EE&T), Newport News, VA. September 7, 2007.
US Environmental Protection Agency. 2002. Implementation Guidelines for the Filter Backwash
Recycling Rule (FBRR). Office of Water. EPA 816-D-01-001.
20