NC0036269_NOV-2019-LV-0572 Response_20190822

August 22, 2019
CERTIFIED MAIL
RETURN RECEIPT REQUESTED
Mr. W. Corey Basinger, Regional Supervisor
Water Quality Regional Operations Section
Mooresville Regional Office
Division of Water Resources, NCDEQ
610 E. Center Avenue, Suite 301
Mooresville, NC 28115
WATER & SEWER AUTHORITY
OF CABARRUS COUNTY
Administrative Offices
232 Davidson Hwy, Concord, NC 28027
704.786.1783 ♦ 704.795.1564 Fax
Rocky River Regional WWTP
6400 Breezy Lane, Concord, NC 28025
704.788.4164 ♦ 704.786.1967 Fax
www.wsacc.org
SUBJECT: NOTICE OF VIOLATION & INTENT TO ASSESS CIVIL PENALTY
TRACKING #: NOV-2019-LV-0572
PERMIT: NCO036269 — ROCKY RIVER REGIONAL WWTP, CABARRUS COUNTY
Dear Mr. Basinger:
This is in response to the subject letter issued by your office on August 6, 2019 and received by
the Water and Sewer Authority of Cabarrus County (WSACC) Administrative Office on August
12, 2019. WSACC acknowledges the exceedance of the NPDES permit parameters for Nitrogen,
Ammonia Total (as N) for the Rocky River Regional Waste Water Treatment Plant (RRRWWTP)
as described in the Notice of Violation. WSACC has already taken remedial actions to correct
this problem and prevent further occurrences. WSACC also contacted the Mooresville Regional
Office (MRO) at the onset of this event, even scheduling a meeting with the MRO staff on April
17, 2019 to discuss plant performance issues. We have remained in contact as we've
progressed through this event.
WSACC experienced a plant upset at RRRWWTP starting in January 2019. It is our belief that a
toxic substance came into the plant and inhibited the nitrification process. Since that time we
have intensified efforts to identify the source(s) that may have contributed to the plant upset.
We were able to identify a major industrial site being decommissioned that discharged a
significant amount of cooling tower water which may have contained algaecides that could
have contributed to the loss of nitrification. During this same period of time, there were
mechanical and maintenance issues at the aeration basins, and with the weakened state of the
plant, we believe the plant could not effectively treat the influent load. From January to June
2019, the RRRWWTP struggled to full nitrification.

Page 2
NOV-2019-LV-0572
August 22, 2019
Starting in February 2019, WSACC contracted with industry experts Maryland Biochemical
Company, Inc. and Brown and Caldwell to assist in identifying the cause of the process upset
and to determine appropriate process enhancements. As part of this effort, WSACC performed
extensive testing on various influent and plant -process related samples to identify potential
sources and influences of toxicity, and WSACC has implemented significant process
enhancements in the last several months to create a more robust set of operating conditions at
the plant. WSACC offers the attached Technical Memorandum from Brown and Caldwell titled
"Loss of Nitrification and Recovery Summary," which includes more specific details as to the
events surrounding the loss of nitrification at the RRRWWTP and the efforts undertaken to
restore the plant to compliance.
WSACC is pleased to inform you that RRRWWTP was in full compliance with all permit
parameters during the month of July 2019 and passed its bioassay that occurred the week of
August 5, 2019 at greater than 100% chronic value.
Please let me know if there is additional information you or your staff need to complete your
evaluation of this unfortunate event. We appreciate any consideration you can give for the
resources, time and effort WSACC invested to resolve the plant nitrification issues we have
been experiencing.
Sincerely,
Mark Fowler
Facilities Director
M F/TH/blc
Encl. Loss of Nitrification and Recovery Summary
ecc: Roberto Scheller (Mooresville Regional Office)
Mike Wilson (WSACC)
file

=Bnweltldwelt
309 E Morehead St., Suite 160
Charlotte, NO 28202
Tel: [phone]
Fax: [phone]
Prepared for: Water and Sewer Authority of Cabarrus County (WSACC)
Project Title: Operations Assistance at the Rocky River Regional Wastewater Treatment Plant (RRRWWiP)
Project No.: 153530
Technical Memorandum No. 3
Subject: Loss of Nitrification and Recovery Summary
Date:
To:
From:
Copy to:
Prepared by:
Reviewed by:
Limitations:
August 20, 2019
Chad VonCannon, PE, Acting Engineering Director
George Anipsitakis
Thomas Hahn, PE, Utility Systems Engineer
Mark Miller, PhD, PE, Process Engineer, License No. 045265, Exp. 12/31/2019
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036485 !
tt�tltlill1111\l�\
George Anipsitakis, PhD, PE, BCEE, Project Manager, License No. 036485, Exp. 12/31/2019
This document was prepared solely for WSACC In accordance with professional standards at the time the services were performed and In
accordance with the contract between WSACC and Brown and Caldwell dated April 4, 2019. This document Is governed by the specific scope of work
authorized by WSACC; It Is not intended to be relied upon by any other party except for regulatory authorities contemplated by the scope of work. We
have relled on Information or Instructions provided by WSACC and other parties and, unless otherwise expressly Indicated, have made no
independent Investigation as to the validity, completeness, or accuracy of such Information.

Loss of Nitrification and Recovery Summary
Executive Summary
This Technical Memorandum 3 (TM-3) summarizes the analyses performed trying to identify the cause of ni-
trification loss at the RRRWWTP and the changes implemented that ultimately led to nitrification recovery
and restoring plant performance. Summaries of investigations, analytical testing, and operational changes
are provided.
Recent testing within the plant and out in the collection system suggested that the plant had been receiving
nitrification inhibiting compounds both internally (recycle streams) and externally. These compounds could
not be identified with certainty. It is believed that a plant upset occurred in January 2019 when a recently
decommissioned industrial facility (Philip Morris) discharged large volumes of cooling water over a long pe-
riod to the sewer system. This slug, which ultimately reached the treatment plant and believed to have con-
tained algaecides, upset the activated sludge biology at the plant. Given the cold temperatures and the fact
that the plant had been operating in a single step (parallel mode) without any protection offered by pretreat-
ment led to a complete loss of nitrification from which the plant could not recover.
Late March 2019, WSACC contacted Brown and Caldwell (BC) requesting assistance since up to that point
no significant improvement in plant performance was realized despite the significant efforts by operating
personnel. BC mobilized early April 2019 and together with WSACC performed a series of tests and opera-
tional changes in an attempt to identify the cause of the upset and restore plant performance as soon as
possible. Finally recovering from this upset took some time as the focus was initially on prevention by identi-
fying the inhibitory compound(s) and removing them or their source from the system. Throughout this period,
WSACC implemented significant analysis and process improvements trying to restore the plant performance.
In late May 2019 it became apparent that the cause of this upset was not going to be easily identified, the
focus was shifted to controls and more drastic actions (changing plant configuration from parallel to partially
series) were taken. The plant was reconfigured to a partially series (two-step) mode with a flow split at a ratio
of 60/40 between Step 1 and 2 on June 3, 201-9. Unfortunately, the plant suffered from nitrite lock for the
majority of June and, even though performance was improved, the weekly ammonia permit limits were still
not met. This nitrite lock condition was identified on June 26, 2019 at which point the flow split was in-
creased to 70/30 between Step 1 and 2 and the Step 1 SRT was reduced to 2 days. These actions elimi-
nated this nitrite lock, restored full nitrification in Step 2 and stabilized the plant's performance. The plant
has been operating without a notable issue for the whole month of July 2019 up to this date.
A timeline of important events is provided in Table ES-1 and final effluent total ammonia nitrogen concentra-
tions for 2019 are provided in Figure ES-1.
Next, it is important that the plant be prepared for the upcoming winter or the future to be able to handle
possible additional upsets that may be the result of lower temperatures and inhibitory compounds that will
continue to be received. Recommendations for future operations are therefore provided in the last section of
this TM-3.
�rown�oCaldwel!
2019-8-20 TM-3 RRRWWTP Loss of Nitrification and Recovery

Loss of Nitrification and Recovery Summary
Date
went
January 2019
Recently decommissioned industrial facility (Philip Morris) discharges large volumes of cooling water over a long period
to the sewer system.
Three sub -basins of Step 2 bioreactor are also drained (one at a time) and brought back online within a period of seven
days to address clogging issues with the aeration mixers.
Treatment declines rapidly resulting in effluent permit violations for ammonia and fecal coliforms (weekly limit) and
high daily concentrations of effluent total suspended solids (no permit violation).
Ability to nitrify is almost completely lost.
March 15, 2019
Bioreactors are seeded with a blend of nitrifying bacteria by Novozymes.
March 25, 2019
WSACC contacts Brown and Caldwell (BC) requesting assistance.
March 27, 2019
Novozymes' representative Kin Ferrell visits the plant fortesting and devising additional seeding plan.
April 1, 2019
Bioreactors are re -seeded with blend of nitrifiers by Novozymes (3-day event).
April 3, 2019
BC visits the plant for the first time.
April 10, 2019
First activity test is performed.
April 25, 2019 -July 10, 2019
More rigorous activity test program is implemented.
May 13, 2019
Plant starts adding polymer upstream of the secondary clarifiers using existing dated equipment.
June 3, 2019
Plant is reconfigured to a partially series (two-step) mode with a flow split at a ratio of 60/40 between Steps 1 and 2.
June 6, 2019
Jartesting is conducted using emulsion polymer.
June 11, 2009 to date
Plant starts renting and testing skid -mounted dry and emulsion polymersystems.
June 13, 2019
Jartesting is conducted using dry polymer.
June 26,2019
Nitrite lock is identified.
Flow split is increased to 70/30 between Step 1 and 2.
June 27, 2019
Step 1 SRT is reduced to 2 days.
July 5, 2019
Weekly ammonia limit of 3.6 mg/L is met forthe first time since initial plant upset.
a FE TAN 30-day TAN
30
1 25
E
20
0
E 15
E
c 10
N
5
w
c 0
u- 1/1/19 1/31/19 3/2/19 4/1/19 5/1/19 5/31/19 6/30/19
Figure ES-1. Final Effluent (FE) Total Ammonia Nitrogen (TAN) Concentrations
BIOWt� +o "atdW�At
7/30/19
2019-8-20 TM-3 RRRWWTP Loss of Nitrification and Recovery

Loss of Nitrification and Recovery Summary
Section 1: Background
The RRRWWTP is a high purity oxygen (HPO) activated sludge system rated for 26.5 million gallons per day
(MGD) that is currently treating 17-20 MGD of medium to high strength wastewater. In the last two years,
the RRRWWTP has been experiencing performance fluctuations. Beginning in January 2019, treatment de-
clined rapidly resulting in effluent permit violations for ammonia (Figure 1) and fecal coliforms (weekly limit;
Figure 2). Uncharacteristically high daily concentrations of total suspended solids (TSS; Figure 3) were also
measured in the effluent, though no permit limit was violated for that parameter. Suppression of nitrification
due to lower temperatures during winter has been observed regularly (at least in winters 2007-8, 2008-9,
2016-17, 2018-19) with multiple reports written by consultants (Hazen, Gilligan, Black & Veatch) trying to
address the problem.
In January 2019, the ability to nitrify was almost completely lost at the RRRWWTP and the plant did not re-
cover when process temperature increased in April and May. Brown and Caldwell (BC) was initially contacted
on March 25, 2019 to mobilize and assist with resolving this situation and visited the plant for the first time
on April 3, 2019.
30 i
.CO
25
0
E
20 i
Q J
4F \
15'aO
ga.
23 E
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RS
C: 5 I
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Apr-16
Oct-16
May-17
Nov-17 Jun-18 Dec-18
Jul-19
ewe]
a 7,000
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E 6,000
5,000
0 4,000
y- U
w 3,000
c_ 0 2,000
LL 6
V 1,000
0
1-Apr
Figure 1. Historical Final Effluent Ammonia
18-Oct 6-May 22-Nov 10-Jun 27-Dec 15-Jul
Brown-Catdwett
3
2019-8-20 TM-3 RRRWWTP Loss of Nitrification and Recovery

Loss of Nitrification and Recovery Summary
Figure 2. Historical Final Effluent Fecal Coliform
Figure 3. Historical Final Effluent TSS
Initial investigations revealed the lack of higher life forms and filamentous bacteria within the biological
flocs, which indicated the presence of toxic compounds in the influent. The lack of filamentous bacteria that
form the backbone of strong flocs resulted in pin flocs with poor flocculation leading to high effluent TSS,
particularly in Step 2. High solids in the effluent often leads to high fecal coliform counts when the disinfect-
ant dose is too low. Early in 2019, WSACC added polymer upstream of the aeration basins at the recommen-
dation of the polymer supplier and, later in spring, switched the feed location to upstream of the each Step 2
secondary clarifier to improve flocculation. Unfortunately, success was limited because of the high dose re-
quired and the limitation of the polymer make down equipment.
Nitrification was consistently inhibited with only short periods where the process seemed to recover. This in-
dicated that the influent toxicity was not constantly entering the plant or at least not at the concentrations
that would cause inhibition. Mechanical and process issues did not appear to be the cause since the efflu-
ent had enough alkalinity for nitrification and the dissolved oxygen (DO) in the HPO basins was high. Carbo-
naceous oxidation appeared to be unaffected suggesting the substance(s) causing the toxicity was(were) not
in high enough concentrations to completely kill the entire biological process.
There have also been concerns about the high usage of pure oxygen and chemical for alkalinity and pH con-
trol. The plant also operates a multiple hearth incinerator, which returns a liquid stream from the scrubber
system back to the main process with high constituent concentrations known to suppress the biological ac-
tivity of the activated sludge process.
BrownANpGatdwett
2019-8-20 TM-3 RRRWWTP Loss of Nitrification and Recovery

Loss of Nitrification and Recovery Summary
Section a Site Visits and Data Review
Several initial and follow-up site visits were conducted by BC personnel to assist the RRRWWTP operations
and lab staff with identifying potential causes of treatment issues. Plant operational data and discharge data
for significant industrial users (SIUs) was requested and reviewed to identify potential sources. Results and
observations from the site visits and data review are provided herein.
2.1 Initial Observations
During the initial site visits it was demonstrated that the activated sludge system did not contain nitrifiers.
Short-term recommendations included dropping the mixed liquor suspended solids (MLSS) down to 3,000-
3,500 mg/L and attempting to regrow the nitrifiers. In addition, BC recommended reducing DO in the oxy-
genation tanks down to approximately 10 mg/L from the observed 20 to 30 mg/L and perform additional
and more frequent testing in the collection system for total Kjeldahl nitrogen (TKN).
The focus during the initial site visits was on the following possible causes for the plant upsets:
1. External or internal constituents causing acute or chronic toxicity to the biomass including:
— Heavy metals.
— Cyanide from the incinerator scrubber blowdown water.
— TKN and organic compounds including quaternary amines (quats) from industrial activity or cleaning
and disinfection products. Literature suggests that as low as 1-2 mg/L of quats are toxic to the bio-
mass. The RRRWWTP had measured once at least 9 mg/L of total quats in the biomass. The
RRRWWTP also receives septage, which may contain substantial amounts of these quats. The
RRRWWTP also receives landfill leachate that has a pretreatment pond that is known to lose nitrifi-
cation during winter.
— Soluble phosphorus deficiency. The RRRWWTP receives water plant sludge containing alum and
powder activated carbon (PAC). Alum can bind soluble phosphorus to a degree that causes defi-
ciency of that nutrient limiting biomass growth.
2. Operational issues that may have been caused by the following:
— Switching to a parallel (single step) operation (October 2016) when literature recommends partially
series (two-step) operation for plants that require year-round nitrification and may receive toxic ma-
terials and organic surges.
— Difficulty in controlling wasting from Step 2 because of hydraulic limitations associated with the par-
allel (single step) operation.
— The draining of several HPO basins in quick succession for cleaning and maintenance of mixers that
had been clogged with rags limiting the oxygen transfer in those basins. WSACC drained several of
these basins in quick succession causing excessive wasting.
— MLSS instead of solids retention time (SRT) control of the biological process resulting in excessive
swings in SRT from one day to the next.
— Operating at a sludge age below the critical SRT for nitrification.
— Limited alkalinity and pH control as demonstrated by insufficient alkalinity (bicarbonate).
The following historical records were reviewed to.document trends and identify any abnormalities:
BrownANo Caldwell
2019-8-20 TM-3 RRRWWTP Loss of Nitrification and Recovery

Loss of Nitrification and Recovery Summary
1. Laboratory data to include influent, primary effluent, secondary effluents, and final effluent constituents
and flows.
2. Operational records and process control data to include incinerator temperatures, HPO DO levels, SRT,
processes in/out of service, and solids concentrations.
3. SIUs' laboratory data, flow contribution, primary business function, and any changes to current opera-
tions.
4. Review of previous reports by Hazen, Black & Veatch (B&V), and Tom Gilligan.
2.2.1 Influent Flows
The annual average influent flow has increased by approximately 57% since 2016 and is approaching the
design capacity of the plant as shown in Figure 4. The combined influent flow includes the Cold Water and
Irish Buffalo (CW+IB) and the Lower Rocky River Pump Station (LRRPS) interceptors. The fall and winter of
2018-2019 had significant rainfall events including two hurricanes and higher than average precipitation, so
some of the high flow values in the year are the result of extreme wet weather events and not necessarily
growth within the sewer basin.
a Combined Influent ® Flow 30-day ® Flow 365-day
70
60
050
75
3 40
0
LL
.., 30
c
a�
20
c
10
141
Apr-16 Oct-16 May-17 Nov-17 Jun-18 Dec-18
Figure 4. Historical Combined Influent Flows
2.2.2 Influent Constituents
Plant operating data for a three-year period from April 2016 through April 2019 were tabulated and were
reviewed. Figure 5 provides a graphical illustration of the influent biological oxygen demand (BOD5), chemi-
cal oxygen demand (COD), TSS, and total ammonia nitrogen (TAN) loads. Influent loads have been climbing
mainly due to an increase in flows. However, TAN has the steepest upward trend as shown in Figure 5. The
same was observed by Hazen in their 2015 BioWin update report.
gown-o Cal.dweit
6
2019-8-20 TM-3 RRRWWTP Loss of Nitrification and Recovery

Loss of Nitrification and Recovery Summary
185,000
165,000
U)
1 145,000
to
a
O
M 125,000
c
c�
r7
85,000
c
0
0
4-
S 65,000
0
c
45,000
0
v
25,000 -
Apr-16
TSS Load a COD Load ® BOD5 Load a TAN Load
40
Oct-16 May-17 Nov-17 Jun-18 Dec-18
—r 12,000
i
I
i
10,000
S 4 II
Memo
4,000
2,000
H]
0
z
0
W
v—
c
0
c
E
0
0
Figure 5. Historical Influent Loadings
Plant influent without recycles, primary influent with recycles, and primary effluent average concentrations
establishing primary clarifier removal efficiency for the same period are summarized in Table I.
Influent
Primary Influent
Primary Effluent
Percent Removal
BOD5(mg/L)
313
286
153
46%
COD(mg/L)
722
680
332
45%
TSS(mg/L)
313
320
74
77%
TAN (mg-N/L)
1 36
28
1 27
1 No removal
TKN (mg-N/L)
Limited data t
52
No data
The recycle streams are less concentrated, at least in the constituents listed. For TKN, review of limited data
suggests that the recycle stream contains almost the same concentration as the RRRWWTP influent.
From the primary influent dataset, the COD to BOD ratio has been 2.4-2.5 and the TKN to TAN 1.8-1.9 on
average when more typical values are 2 and 1.3, respectively. This is an indication of higher organic nitrogen
compounds than typical. This could include such compounds as quats.
�rown�oCaldwet!
7
2019-8-20 TM-3 RRRWWTP Loss of Nitrification and Recovery

Loss of Nitrification and Recovery Summary
2.2.2.1 Influent TKN
High concentrations of TKN have been measured sporadically in the collection system and in the RRRWWTP
influent. TKN has been historically measured once a month, but additional data was collected recently for
this evaluation to identify potential sources of inhibition. The LRRPS interceptor historically has higher con-
centrations and flows than the CW+IB side of the collection system. Figure 6 summarizes recent TKN data.
High spikes of TKN can be observed while TAN concentrations remained relatively stable.
TKN ®TAN
180
160
140
120
100
80
60
40
20
Apr-16 Oct-16 May-17 Nov-17 Jun-18 Dec-18
Figure 6. Combined Influent TKN and TAN Concentrations
Additional sampling of the CW+IB and LRRPS interceptors was conducted and higher than normal TKN con-
centrations were detected in both interceptors (Figure 7). The spikes in the CW+IB were not as sustained as
the LRRPS. Due to these abnormally high TKN concentrations, it was suspected that the inhibition issues
were indeed coming into the plant through the collection system. However, high TKN in the influent was not
a new issue. Figure 8 below from the 2011 Hazen Rerate Report shows some limited TKN data in the influ-
ent from September 2007 to June 2009. Some high values were also observed during this period.
140
120
100
E 80
Z 60
Fes- 40
20
I
3/1/19
® -CW+IB TKN -LRRPS TKN
3/11/19 3/21/19 3/31/19 4/10/19 4/20/19 4/30/19 5/10/19 5/20/19 5/30/19
Figure 7. Collections System TKN Concentrations
BrownAw Catdwelt
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2019-8-20 TM-3 RRRWWTP Loss of Nitrification and Recovery

Loss of Nitrification and Recovery Summary
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Figure 8. Influent TKN Data from September 2007 through June 2009 (Figure 3-5 from Hazen Report)
2.2.3 SRT
A comparison of final effluent ammonia and the aerobic SRT (aSRT) for each HPO step is provided in Figure
9. The aSRTs have been too low historically and changed erratically from one day to the next because
WSACC has historically been adjusting wasting to maintain a certain MLSS concentration and solids inven-
tory rather than aiming for a certain SRT, When there are performance issues, the plant seems to be wasting
less leading to an increase in the aSRTs, but this reaction is too late. As shown in Figure 10, the aSRT of
Step 1 has been particularly low, even after switching to a parallel operation. Step 1 may have been perform-
ing better at lower aSRTs because it was underloaded, its primaries had higher hydraulic retention times
(HRT) and had more secondary clarifier capacity for the portion of flow it received (longer overall SRT and
HRTs). Note that the SRT of both Step 1 and Step 2 were higher (red rectangle) than historically in the winter
of 2017-18 when ammonia bleed through was suppressed unlike the winters of 2016-17 and 2018-19.
gown o C ildweIt
9
2019-8-20 TM-3 RRRWWTP Loss of Nitrification and Recovery

Loss of Nitrification and Recovery Summary
30
J 25
Z
ao
E 20
r�
0
4/1/2016
2.2.4 Metals
o NH3-N a MCRT Stp I A MCRT Stp II
10/18/2016 5/6/2017 11/22/2017 6/10/2018 12/27/2018
Figure 9. Comparison of Final Effluent Ammonia and WWTP Aerobic SRTs
30
25
Metals data for the plant influent, effluent, mixed liquor, and SIUs was reviewed. Additional mixed liquor
samples were collected from Steps 1 and 2 to investigate possible heavy metal inhibition. Zinc (2.3-1.6
mg/L) and copper (0.7-0.8 mg/L) were found to be elevated but were not significant enough to raise any
concerns. Historical data that was reviewed also had elevated concentrations of zinc and copper during nor-
mal operational conditions. Additionally, SIUs' metals data were all similar to historical concentrations.
Additional sampling of plant recycles including scrubber blowdown, thickener overflow, and ash pond water
was conducted but none of the streams contained concentration of metals that would be of concern for inhi-
bition.
2.2.5 Cyanide
Cyanide that is present in incinerator scrubber blowdown water is a known inhibitor of nitrification at concen-
trations as low as 0.3 mg/L. Previous reports (2017) included analysis of the scrubber water that ranged
from 4.6 to 14.8 mg/L as total cyanide. During the previous winters, the treatment plant had struggled to
maintain complete nitrification and this can likely be attributed to cyanide inhibition that is more severe at
colder temperatures. Based on previous plant experience, nitrification rates would improve when the inciner-
ator was taken out of service for maintenance.
2.3 SIUs
The SIUs (Table 2) were contacted by WSACC to determine if any changes in production, chemical usage, or
operations were made. For certain industries additional data was requested including receiving logs. It was
identified that in January 2019, during decommissioning, a Phillip Morris site discharged in the sewer large
quantities of cooling tower water. It was believed that this initial event is what caused the first loss of nitrifi-
cation since cooling water often contains biocides for algae control. Algae die off was also noted in the sec-
ondary clarifiers and effluent channels at the plant. No further discharges were reported from this site.
Brown-oCaldwell
10
2019-8-20 TM-3 RRRWWTP Loss of Nitrification and Recovery

Loss of Nitrification and Recovery Summary
Americhem
Color resin
44,000
BFI Waste Systems
Landfill
150,000
Charlotte -Meek.
Municipal
4,000,000
Charlotte -Meek.
Municipal
2,000,000
CHS-Northeast
Hospital
85,000
CHS-Northeast
Hospital
70,000
City of Concord
Water Plant
1,600,000
Galvan Industries
Galvanizing
3,000
HeiQ Chem -Tex
Textile
20,000
Heritage Crystal Clean
CWi-Oil
86,000
Organic Dyes & Pigments
Dyes & Pigments
3,000
Owens Corning
Furnace Parts Mfg.
4,000
Perdue Farms
Poultry
500,000
Star America
Textile
75,000
Stericycle
Medical Waste
32,000
Stericycle
Medical Waste
13,000
The highest flow contributor on the LRRPS interceptor is Charlotte Water (4.9 MGD) with some of its
wastewater containing higher than typical COD and ammonia loads (CMUD-05). Other lower flow contributors
on the LRRPS side include the BFI landfill (0.055 MGD), solids from the City of Concord water plant (0.15
MGD) and Heritage Crystal Clean (0.045 MGD), a centralized waste treatment facility that also treats oily
wastewater. All contain high COD and/or high ammonia concentrations, but the mass loadings are relatively
low. In the past, no TKN data was collected from the SIUs, but for this recent evaluation, TkN data was col-
lected from selected SIUs.
Heritage Crystal Clean (HCC) did not initially report treatment issues at their facility, but later reported treat-
ment process upsets occurring on and off in April 2019 with high effluent TSS and ammonia concentrations.
HCC was able to identify the customer that was causing treatment issues and switched from liquid treatment
to pit solidification. By switching the treatment method, the customer's waste would no longer be present in
HCC's discharge. However, no improvement at the RRRWWTP occurred after HCC's treatment processes re-
covered.
2.4 Previous Reports
The previous reports completed by other consultants were reviewed and the primary findings and recom-
mendations are provided here.
2.4.1 Thomas Gilligan, Evaluation Report, August 2017
The driver for this report was to investigate the effluent limit violations in December 2016 through February
2017. Main findings of this report included the following:
Brown-DCaldwett
11
2019-8-20 TM-3 RRRWWTP Loss of Nitrification and Recovery

Loss of Nitrification and Recovery Summary
Previous operation of wasting from Step 2 to Step 1 had the benefit of keeping the nitrifiers in the sys-
tem.
Reasons for excursion included insufficient oxygen transfer due to impeller clogging/blockage, too high
nitrifier waste rate (i.e., low SRT), and too low reactor pH (<6).
The report summarized data in a tabular monthly average format of several operating parameters from July
2015 through May 2017. The report had a few recommendations including replacing the older mixers that
had been prone to clogging. This recommendation has been implemented in phases and was recently com-
pleted. Another recommendation was to reduce the vent oxygen purity to 45-50 % to reduce operation
costs. This recommendation was recently implemented following discussions with BC.
2.4.2 B&V, Nitrification Discussion, March 8, 2017
The driver for this report was also to investigate the effluent limit violations in December 2016 through Feb-
ruary 2017. The report discussed the switching from a partially series to a parallel operation, the limiting
SRT, and a possible inhibitory compound as the reasons for the ammonia limit exceedances. The data plots
in that report clearly show that the ammonia increase in the effluent started in early November 2016 imme-
diately after the process configuration was changed. Longer SRTs did not help with nitrification but the SRTs
never exceeded 10 days. The report recommended increasing SRTs to 15 days. BC also recommended in-
creasing the SRTs to values greater than 10 days. B&V's recommendations also included checking for cya-
nide and metals and increasing the bioreactor pH to values above 6.5.
2.4.3 Hazen, RRRWWTP BioWin Model Update, November 9, 2015
The Hazen rerate report and model (original and update) discusses partially series operation with an 85/15
split (always for dry weather) and even a 90/10 split if ammonia and TKN were still an issue. In this mode,
Step 1 would receive 85 or 90 percent of the plant influent flow whereas Step 2 would receive the remaining
influent portion plus all the effluent from Step 1. To combat the high solids in the secondaries of Step 2,
Step 2 needs to run at a lower MLSS of 2,200-2,800 mg/L. Until June 2019, WSACC had never implemented
a two -stage process that went beyond a 60/40 influent flow split between the two steps.
Brawn -a Catdwett
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Loss of Nitrification and Recovery Summary
Section 3: Recommendations and Steps to Recovery
This section outlines the initial recommendations made prior to the process recovering and the steps that
were taken to implement these recommendations.
3.1 Plant Re -seeding
In an attempt to rapidly recover the treatment process, plant staff purchased Novozymes bioaugmentation
products based on the recommendations of Kin Ferrell (Maryland Biochemical Co.) and reseeded the pro-
cess. A blend of dry heterotrophic bacteria (BioRemove 5100) and liquid autotropic nitrifiers (BioRemove
5805) were added to Step 1 and 2 on two occasions; once on March 15, 2019 and on April 1 through 3,
2019. Each day nitrifiers were added, the effluent ammonia would improve, but only temporarily suggesting
that inhibitory compounds were preventing the process from recovering.
3.2 Supplemental Alkalinity and pH Control
Due to the configuration of HPO processes, carbon dioxide becomes elevated in the headspace of the reac-
tors and as a result increases the fraction that is dissolved in solution, which depresses the pH. Since low pH
(<6.5) can inhibit nitrification, it was recommended to increase supplemental alkalinity addition to ensure
excess alkalinity was available for nitrification and the pH was maintained >6.5 in all of the reactor cells at
all times.
The plant staff followed this recommendation by dosing supplemental alkalinity to obtain 100-200 mg/L of
alkalinity as calcium carbonate in the final effluent.
3.3 SRT Control
To assist the plant with operating using SRT control instead of MLSS control, BC developed an SRT calcula-
tion spreadsheet that could be used by staff to estimate the daily pounds of solids to be wasted from each
Step. This SRT calculation spreadsheet was sent to WSACC on April 25, 2019 to be used in implementing
the recommendation for a minimum SRT of 15 days in each step when operated in parallel mode. The plant
staff implemented this recommendation but struggled to maintain a consistent SRT at first because of highly
variable effluent TSS.
3.4 Outside Liquid and Solid Wastes
To help narrow down the source of inhibition in the plant, it was recommended to stop receiving all outside
liquid and solid wastes where feasible. Prior to this recommendation, the plant had already stopped receiv-
ing all septage waste, water treatment plant solids (discharged via collection system), and ERCO sludge
slurry (rendering plant). No improvement in plant performance was observed several weeks after stopping all
imports of liquid and solid wastes.
The imported solids that were not cut off were from the Rock Hill WWTP. Since these solids arrive as de -
watered sludge and are fed directly to the incinerator, it was assumed that there would be little to no impact
on the liquid treatment processes. The Rock Hill WWTP also did not report any treatment issues.
Prior to recovering, water treatment plant solids were allowed to be discharged again. Since these solids
contained activated carbon it was assumed that these solids may actually help the plant recover by absorb-
ing any potentially toxic organic chemicals. Septic haulers were also allowed to resume discharging at the
plant since no improvement to the process was observed.
Brown-Ceidweii
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Loss of Nitrification and Recovery Summary
3.5 Sampling and Testing
It was recommended by BC that additional sampling and bench top testing be conducted to try and track the
source of inhibition. This included sampling of internal recycle streams (i.e., scrubber blowdown water), SIUs,
and different sites within the collection system.
3.5.1 Nitrogen Monitoring
It was recommended to continue testing more frequently for TKN in the influent and secondary effluents in
order to determine the organic nitrogen contribution. Typical municipal effluent organic nitrogen concentra-
tions vary from 1-3 mg-N/L. Reviewing historical organic nitrogen data revealed that plant experiences peaks
as high as 5-10 mg-N/L. This was also observed in the additional sampling data. It was suspected that an
inhibitory compound that was organic in nature was entering the plant. A few samples were sent off for vola-
tile organic compounds (VOCs) and organo-pesticides analysis, but the results did not show influence from
those compounds.
3.5.2 Phosphorus Monitoring
After reviewing historical data, it was determined that soluble phosphorus was not limiting the process. The
average final effluent total phosphorus was almost always >2 mg-P/L. Several secondary effluent grab sam-
ples also confirmed that there was sufficient ortho-phosphate present in the secondary effluent.
3.5.3 Metals
Additional sampling of plant recycles including scrubber blowdown, thickener overflow, and ash pond water
did not contain metals concentrations that would be of concern for inhibition.
3.5.4 Cyanide
Additional samples were taken from the CW+IB and LRRPS interceptors and analyzed for cyanide. All the re-
sults were below the detection limit (0.005 mg/L total cyanide) for the method. Incinerator scrubber blow -
down samples varied between 0.7 to 9.7 mg/L with an average concentration of 3.4 mg/L. Primary effluent
concentrations varied between 0.03 to 0.55 mg/L with an average concentration of 0.21 mg/L. While this
level of cyanide likely causes chronic reduced nitrification rates, the process should have been able to han-
dle these concentrations after the temperature increased from the winter lows. However, this was not the
case.
BC recommended increasing the incinerator afterburner temperatures to limit the production of cyanide but
after reviewing this recommendation with plant staff, it was determined that this what not a viable option
because of the condition and reliability of the existing equipment. Operational experience had only shown a
modest increase in afterburner temperature while using an excessive amount of supplemental fuel.
BC also investigated alternative recycle locations for the scrubber water to dampen the inhibitory effects, for
example to the gravity thickeners. However, no alternatives were viable because of the quantity of scrubber
blowdown water (1-1.5 MGD) and lack of alternative piping.
3.5.5 Batch Activity Testing
To determine the source of nitrification inhibition, batch activity tests were performed for several months us-
ing Muddy Creek WWTP mixed liquor and various samples collected from internal plant recycle streams,
sites within the collection system, and samples directly from the SIUs. The first activity test was performed
on April 10, 2019. A more rigorous activity test program was implemented on April 25, 2019 and lasted until
July 10, 2019. The nitrification rates from these tests were compared to control rates measured using
Muddy Creek mixed liquor and influent. The observations from these are summarized below:
BrownAND( wetE
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Loss of Nitrification and Recovery Summary
Scrubber blowdown water was acutely toxic to the Muddy Creek mixed liquor. Since Muddy Creek does
not have incinerators, the activated sludge process has never been exposed to cyanide and therefore
was not expected to be acclimated to treat cyanide. These results confirmed that the scrubber blow -
down water was inhibitory.
Primary influent and effluent samples were also inhibitory to the Muddy Creek mixed liquor although not
to the extent of just scrubber blowdown water. These results indicated that cyanide was causing chronic
inhibition in both treatment steps.
All other internal plant recycles (i.e., ash pond water, dewatering centrate) did not inhibit nitrification in
the batch activity tests.
The CW+IB interceptor did not appear to be inhibitory but could not be completely ruled out because
some samples did appear to cause inhibition.
Inhibition was observed on the LRRPS line although not to the extent of the primary influent. High TKN
values were also observed in the LRRPS influent that appeared to occur on a weekly basis which sug-
gests it is associated with an industry. These observations led to additional activity testing using differ-
ent samples collected from the lines that feed into the LRRPS. Of these, the Coddle Creek interceptor
was identified as a potential source of inhibition.
Additional sampling was conducted on the lines that feed the Coddle Creek interceptor to continue to
track the source of inhibition. This included taking samples from the collection system just down stream
of the SIUs that discharge to the Coddle Creek interceptor. From this testing, Heritage Crystal Clean
(HCC) and S&D Coffee and Tea (not an SIU) were identified as possible inhibition sources.
• S&D Coffee and Tea samples were inhibitory, but it was due to the low pH, which was corrected with pH
control and dilution of the sample.
Heritage Crystal Clean exhibited inhibition that was at times severe. The HCC samples were also prone
to foaming suggesting high surfactants and possibly disinfectants or emulsifiers that can cause inhibi-
tion. This inhibition was reduced when the HCC samples were blended with Muddy Creek influent to a
more realistic dilution based on HCC's flow contribution to the LRRPS interceptor.
BFI landfill leachate samples did not appear to have any adverse effects on nitrification.
The most recent batch activity tests using mixed liquor from Step 2 after the process recovered indicates
that the LRRPS line still contains inhibitory compounds that are likely causing some chronic inhibition.
However, since the plant has been reconfigured to a partially series operation and Step 1 is now treating
most of the influent flow, any toxic compounds, including cyanide, are getting reduced prior to Step 2.
3.5.6 Whole Effluent Toxicity Testing
Additional final effluent samples were submitted to Environmental Testing Solutions for toxicity testing using
various treatment methods to reduce the toxic effects of ammonia, metals, oxidizers, and organic com-
pounds. These tests indicated that effluent toxicity could be reduced if the sample was treated for metals or
oxidizers. A second round of testing found similar results, but the effluent toxicity increased when subjected
to filtration for the ammonia and organics removal treatments. It was speculated that filtration released the
toxic compounds from the solids or changed the composition of the toxic compound(s) into a more toxic
form.
3.5.7 Foaming
When the treatment process first started to decline, white foam appeared on the effluent troughs of the sec-
ondary clarifier. A defoamer agent had to be added to several manholes where this foam would accumulate.
The foam was not biological in nature and was suspected to be a result of surfactants that were not getting
removed in the treatment process.
Brownmo Caldwett
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Loss of Nitrification and Recovery Summary
As the process began to recover, nuisance foaming became an issue in both treatment steps but more so in
Step 1. Foam samples had to be sent off for microscopic inspection and filament identification because the
plant lab's microscope does not have the magnification and phase contrast capabilities to visualize fila-
ments. The microscopic results found that the foam was caused by Nocardia. To reduce foaming, BC recom-
mended lowering the SRT of Step 1 to washout the filaments.
3.6 Polymer Addition
Due to high effluent solids, which has been a recent issue, flocculation and settling issues were evaluated to
identify the cause. Settling and flocculation tests were conducted that demonstrated the process was floccu-
lation limited and the high effluent solids were not the results of poor settling (i.e., high SVI) or secondary
clarifier issues. Microscopic observations of the flocs also supported the testing observations. Although the
HPO process was operated at high SRTs, the flocs were small and appeared to lack the backbone of fila-
ments. However, the lab's microscope was not good enough to clearly identify filaments due to lack of mag-
nification and phase contrast. The lack of filaments and higher life forms also suggested the presence of in-
hibitory compounds.
The high effluent solids also had a significant impact of the plant's ability to maintain a high SRT. At times,
wasting was stopped completely to allow solids to build within the process. While it was not confirmed, stop-
page of wasting can allow the accumulation of inhibiting compounds if they accumulate in the solids. For ex-
ample, heavy metals can accumulate in the solids.
To improve solids capture, the plant added polymer to the secondary clarifiers. Jar testing was conducted on
June 6 (emulsion polymer) and June 13, 2019 (dry polymer) to identify the optimal dosing rate and polymer
make up concentration. To achieve the optimal target dosing rate, the plant had to increase the polymer
make up concentration until the limit of the existing equipment was met. This resulted in excessive man
hours to make up polymer and keep the equipment running. As a result, the plant has been renting and test-
ing skid -mounted dry and emulsion polymer systems since June 11, 2019 to date. The goal is to compare
the two types of polymer feed systems and implement the one that meets the plant's need in a permanent
installation. These rental polymer feed systems have been used to obtain the polymer doses necessary to
meet effluent TSS limits.
3.7 Preliminary Modeling
To evaluate whether the process was overloaded from an influent TKN and ammonia load standpoint and
that this was causing treatment issues, biological process modeling was performed utilizing an existing
BioWin model of the plant. The model was also used to compare series operation to parallel operation since
parallel operation had never been simulated before. BC received the BioWin model file from Hazen that was
calibrated and validated during their work as reported in TM titled Rocky River Regional WWTP BioWin Model
Update (November 9, 2015). Effluent and influent loads used in that effort are summarized in Table 3.
Condition
Flow
(MGD)
CBOD5
(mg/0
COD
(mg/L)
TSS
(mg/L)
TKN
(mg-N/L) `
TAN
(mg-N/L)
TP
(mg-P/L)
Min Day
16.4
28,800
93,900
40,000
7,080
3,540
1,100
Average Day
19.7
49,700
157,000
78,500
9,270
4,800
1,610
Max Month
21.1
58,800
-
101,000
-
5,210
-
MaxWeek
1 26.6
1 85,700
1 -
138,000
6,370
Max Day
44.9
104,000
292,000
184,000
14,800
9,440
1,900
Brown-oGaldvueil o
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Loss of Nitrification and Recovery Summary
The model Hazen provided was calibrated when the plant was operating in a partial series mode and the ni-
trification maximum growth rate of Step 1 was reduced from 0.9 to 0.5 d-1 to account for inhibition caused
by the sidestreams and recycles at the plant. Without making significant modifications to the model, parallel
operation was simulated using the same reduced nitrifier growth rate in both steps. The results from this
model run suggests that the process should be able to fully nitrify at warmer temperatures. At lower temper-
atures, ammonia excursions were predicted but the weekly and monthly averages were below the winter per-
mit limits.
Since higher than expected TKN values have been measured in the influent and the average influent flows
have been high for the past year, the influent itinerary was modified to account for these observations. This
included increasing the average influent flow from 19 to 25 MGD and decreasing the influent ammonia to
TKN fraction from 75% to 50% by keeping the same average influent ammonia and increasing the influent
TKN. This run resulted in more effluent ammonia excursions during both warm and cold temperatures and
the weekly and monthly average effluent ammonia often exceeded the permit limits. This run indicates that
the RRRWWTP, if operated in a parallel mode, cannot treat the influent TKN and ammonia loads with the
same level of inhibition determined by Hazen's work.
Using the same elevated influent flows and TKN concentrations, partially series operation was simulated at
three different influent splits: 1) 60% Step 1 and 40% Step 2; 2) 70% Step 1 and 30% Step 2; and 3) 80%
Step 1 and 20% Step 2. The previous modeling by Hazen demonstrated that the RRRWWTP should be able
to treat 30 mg/L ammonia and 26.5 MGD at 85:15 and 90:10 splits assuming only a reduced nitrification
growth rate in Step 1. To include some conservatism, a slightly reduced growth rate was also used in Step 2
since a larger portion of influent will be sent to Step 2 than what was assumed in the Hazen work.
Nitrification reliability increased as the split of influent to Step 1 increased with best performance at 80:20.
At the 60:40 split, some nitrification occurred in Step 1 because a longer SRT (5 days) could be obtained.
Note Step 2 waste solids were not directed to Step 1 in the model. As the flow to Step 1 increases, the SRT
must decrease to maintain a manageable MLSS concentration. Reducing the organic carbon load to Step 2
then allows to operate at a higher SRT which benefits nitrification. Other than for hydraulic purposes, it is
beneficial to send some influent to Step 2 to maintain a healthy biomass that settles well.
Based on the field observations to date and the preliminary modeling work performed, Brown and Caldwell's
recommendation was that the RRRWWTP transition back to operate in a partially series mode (two-step)
from parallel mode so that the toxic compounds, both internally generated and those present in the influent,
are treated in Step 1. On June 3, 2019, It was recommended that the plant first start with a 60:40 split since
operations staff have experience only up to this split with this mode of operation. This was immediately im-
plemented. Once the plant staff is comfortable with the 60:40 split, it was recommended to increase the in-
fluent split to Step 1 gradually until a split closer to 85:15 is obtained if possible based on known hydraulic
bottlenecks.
As the plant transitions and adjusts to this partially series mode, it was recommended to continue activity
testing and source tracking to identify the source of external inhibition,
3.8 Switching to Partially Series Operation
The plant staff implemented all the following recommendations in an attempt to recover full nitrification:
m Maintained 100-200 mg/L as calcium carbonate in the final effluent to ensure alkalinity was not lim-
iting.
Targeted a minimum SRT of 15 days in both steps while in parallel mode by utilizing the SRT calcula-
tor spreadsheet provided by BC.
0 Maintained a minimum DO of 10 mg/L in all cells.
=rownA.oCa�ldwell
8?L
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Loss of Nitrification and Recovery Summary
® Reduced vent oxygen purity.
® Maintained consistent and stable incinerator operation.
It was apparent after following BC's initial recommendations that the plant was not going to recover. There-
fore, it was recommended to convert the plant from a parallel operation back to a partially series operation.
The following actions were therefore taken, and the following results were observed:
1. On June 3,2019, the plant implemented an initial split of influent flow between the two steps at a 60/40
ratio as had been done in the past. The plant seemed to stabilize with this modification, but ammonia
was stuck at approximately 9 mg-N/L. A target SRT of 5 days for Step 1 and >15 days for Step 2 was
recommended.
2. Next, the team agreed to increase contributions to Step 1 by 10 percent increment per week and ob-
serve plant performance. As a result, on June 26, 2019, the plant implemented a flow split of 70/30
between the two steps. On the same day, grab samples from secondary effluent indicated nitrite had
accumulated in the first step resulting in a condition known as nitrite lock. Under this condition, the pro-
cess becomes self -inhibiting. Typically, nitrite lock is identified when a disinfection system becomes
taxed because of the additional chlorine demand associated with oxidizing the nitrite to nitrate. In the
presence of ammonia, chlorine reacts with ammonia and forms chloramines. These chloramines reduce
the impact of nitrite on chlorine demand so the disinfection system at the plant was never fully taxed.
Nitrite present in the effluent from Step 1 was also resulting in nitrite lock in Step 2. Once this was iden-
tified, WSACC and BC discussed decreasing the SRT of Step 1 to 1.5-2 days to effectively washout the
nitrifiers and reduce the concentration of nitrite sent to Step 2. This was implemented on June 27,
2019. As soon as nitrification was lost in Step 1, Step 2 transitioned to full nitrification and ammonia
was reduced below the permit limits. Significant foaming that was observed. in the Step 1 RAS piping
network was also suppressed to manageable levels once the Step 1 SRT and the RAS flowrate was re-
duced. Lime addition for alkalinity control to Step 1 was also reduced significantly in an attempt to dis-
rupt nitrification and control foaming in Step 1. The plant has been performing well and meeting all per-
mit limits ever since as shown in Figure 10.
3
J0
25
E
0 20
.E
0
E 15
E
Q
10
N
5
W
0
u- 1/1/19
e FE TAN 30-day TAN
1/31/19 3/2/19 4/1/19 5/1/19 5/31/19 6/30/19
Figure 10. Historical Final Effluent Total Ammonia Nitrogen Concentrations
BrownAND( we[t
18
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Loss of Nitrification and Recovery Summary
Section 4: Final Recommendations
Currently, the RRRWWTP is performing well as also aided by the higher summer temperatures that increase
biological activity. To prepare the plant for cold weather when nitrification is suppressed and to avoid inhibi-
tion or complete loss of nitrification again, it is important that certain measures be considered and possibly
undertaken in the short and longterm.
In the short-term, the following actions should be evaluated and possibly implemented:
1. Continue to operate a two-step process (partial series mode) and address any possible hydraulic bottle-
necks that may prevent an even greater flow split between the two steps in the future. In winter, once
temperatures drop and nitrification rates reduce, the plant may have to implement an even greater split,
to 80/20 or more, between Step 1 and Step 2. It is therefore important to be able to prepare for this
higher split and address any hydraulic limitations (i.e., foaming) that the plant may experience. A de-
tailed analysis of the foam in Step 1 may offer insights on ways (i.e., chemicals) that can suppress or
eliminate it.
2. If signs of nitrification inhibition continue to persist even after a greater influent flow split between Step
1 and 2 is implemented, consider increasing Step 2 SRT further; specifically targeting biodegradation of
cyanide. Relatively simple tests and calculations can be performed to determine the minimum SRT for
cyanide removal.
3. Assess secondary clarifier performance and capacity. The secondary clarifiers are peripherally fed and
may not be currently optimized. Computational fluid dynamic (CFD) modeling may reveal possible en-
hancements in the form of additional baffles that could improve the sedimentation process.
4. Construct a permanent polymer feed system and evaluate the current location and possible need for
mixing of the polymer fed to the secondary clarifiers.
5. Correct the WAS metering and control limitations currently experienced at Step 2.
6. Upgrade microscopic inspection capabilities for filament identification and quantification.
7. Evaluate process instrumentation to detect treatment issues. For example, install an ammonia analyzer
at the effluent flume to detect process upsets early on.
8. Modify routine sampling plan to include critical parameters at greater frequency and more locations (i.e.,
TKN).
Long-term options that could be considered for implementation alone or under a greater plant expansion
project include the following:
1. Add additional venting capabilities in the last zone of the aerated bioreactors to reduce or eliminate the
carbon dioxide buildup and improve pH control.
2. Divert scrubber blowdown water or additional recycle flows to Step 1 only.
3. Implement side stream biological treatment to incinerator scrubber, centrate, thickener overflow or all
recycle streams combined.
4. Construct permanent foaming control structures like classifying selectors that would allow wasting foam
from the activated sludge process directly into the gravity thickeners or centrifuges.
5. Add powdered activated carbon (PAC) to Step 2 bioreactor or elsewhere (i.e., primary clarifiers) to target
organics if further testing reveals that such compounds cause nitrification inhibition problems. PAC will
be removed with the sludge. Some effects of abrasion to piping and equipment should be expected.
6. Construct offline flow equalization facilities for wet weather control.
7. Construct anoxic tanks upstream of the aerated bioreactors and provide internal mixed liquor recycle
pumping to improve sludge settling, recover alkalinity and increase the biomass inventory.
8. Switch to another intensified treatment technology that does not rely on aeration with pure oxygen.
2019-8-20 TM-3 RRRWWTP Loss of Nitrification and Recovery