NC0024333_Authorization to Construct_20040719

NPDES DOCUMENT SCANNING: COVER MEET
NC0024333
Monroe WWTP
NPDES Permit:
Document Type:
Permit Issuance
Wasteload Allocation
Authorization to Construct (AtC)'
Permit Modification
Complete File - Historical
Engineering Alternatives (EAA)
Correspondence
Owner Name Change
Plan of Action
Instream Assessment (67b)
Speculative Limits
Environmental Assessment (EA)
Document Date:
July 19, 2004
This document is printed on reuse paper - ignore any
content on the rezrerise wide

Michael F. Easley, Governor
State of North Carolina
William G. Ross, Jr., Secretary
Department of Environment and Natural Resources
Alan W. Klimek, P.E., Director
Division of Water Quality
July 19, 2004
Mr. Russell Colbath, P.E.
Director of Water Resources
City of Monroe
P.O. Box 69
Monroe, North Carolina 28111-0069
Subject: Authorization to Operate
ATC Number 0024333A01
Monroe WWTP
NPDES Permit NC0024333
Union County
Dear Mr. Colbath:
A request for an Authorization to Operate was received by the Division of Water Quality,
November 23, 2003, with additional supporting information being submitted March 19 and June
28, 2004. Authorization is hereby granted for the re -rating of the City of Monroe's Wastewater
Treatment Plant (WWTP) from 9 MGD to 10.4 MGD. At this time, no changes in treatment
components are proposed. The City's consultant provided calculations and information to support
a hydraulic re -rating of the plant to 10.4 MGD.
The Division of Water Quality offers the following comments with regard to the re -rating:
• In approval of this Authorization to Operate, the Division of Water Quality has relied on the
actual operating data at the increased flow, as presented by the City's consultant.
Traditionally, nitrification requires a greater detention time than what is, and will be, used
at the City. As stated below in this Authorization to Operate, in the event that the facilities
fail to perform satisfactorily at the increased design flow, the City of Monroe shall take
corrective action, such as the construction of additional wastewater treatment units.
• The City must comply with the requirements set forth in 15A NCAC 2H .0223 (1) and (2).
This rule requires that the City demonstrate future wastewater treatment capability should
the average flow for the calendar year reach 80% or 90% of permitted capacity. The
Division views the re -rating to 10.4 MGD as a temporary measure. Should Monroe exceed
the 80 or 90% of design flow in a calendar year, the City may be subject to flow
moratorium.
• For compliance purposes. limit/monitoring requirements for 10.4 MGD must be met
beginning September 1. 2004. The final NPDES permit will be issued concurrently with
this Authorization to Operate (under separate cover).
With this Authorization to Operate, the permittee is approved to operate the Monroe WWTP at
a design f ow of 10.4 MGD, with permitted limits as specified in the 1VPDES permit issued July
19, 2004.
The sludge generated from these treatment facilities must be disposed of in accordance
with G.S. 143-215.1 and in a manner approved by the North Carolina Division of Water Quality.
In the event that the facilities fail to perform satisfactorily, including the creation of
nuisance conditions, the Permittee shall take immediate corrective action, including those as may
be required by this Division, such as the construction of additional or replacement wastewater
treatment or disposal facilities.
North Carolina Division of Water Quality
1617 Mail Service Center
Raleigh, North Carolina 27699-1617
[phone]
FAX [phone]
On the Internet at http://h2o.enr.state.nc.us/

Mr. Colbath
Page 2
Upon classification of the facility by the Certification Commission, the Permittee shall
employ a certified water pollution control treatment system operator to be in responsible charge
(ORC) of the water pollution control treatment system. The operator must hold a certificate of the
type and grade at least equivalent to or greater than the classification assigned to the water
pollution control treatment system by the Certification Commission. The Permittee must also
employ a certified back-up operator of the appropriate type and grade to comply with the
conditions of Title 15A, Chapter 8G, .0202. The ORC of the facility must visit each Class I facility
at least weekly and each Class II, III, and IV facility at least daily, excluding weekends and
holidays, and must properly manage and document daily operation and maintenance of the facility
and must comply with all other conditions outlined in Title 15A, Chapter 8G, .0204. Once the
facility is classified, the Permittee must submit a letter to the Certification Commission which
designates the operator in responsible charge within: (A) Sixty calendar days prior to wastewater
being introduced into a new system or (B) within 120 calendar days of the following, (i) after
receiving notification of a change in the classification of the system requiring the designation of a
new ORC and back-up ORC or (ii) a vacancy in the position of ORC or back-up ORC.
A copy of the Authorization to Operate shall be maintained on file by the Permittee
for the life of the facility.
The Operational Agreement between the Permittee and the Environmental Management
Commission is incorporated herein by reference and is a condition of this Permit. Noncompliance
with the terms of the Operational Agreement shall subject the Permittee to all sanctions provided
by G. S. 143-215.6 for violation of or failure to act in accordance with the terms and conditions of
this Permit.
Failure to abide by the requirements contained in this Authorization to Operate may
subject the Permittee to an enforcement action by the Division of Water Quality in accordance
with North Carolina General Statute 143-215.6A to 143-215.6C.
The issuance of this Authorization to Operate does not preclude the Permittee from
complying with any and all statutes, rules, regulations, or ordinances which may be imposed by
other government agencies (local, state, and federal) which have jurisdiction.
One (1) set of approved calculations is being forwarded to you. If you have any questions
or need additional information, please contact Ms. Susan A. Wilson, P.E., telephone number (919)
733-5083. extension 510.
cc: Central Files
NPDES Unit. Permit File
Mooresville Regional Oliic
Mr. Jim Cramer, P.E.
Sincerely,
Alan W. Klimek, P.E.
e, Water Quality
Hazen and Sawyer. P.C.
4011 WestChase Boulevard
Raleigh, NC 27607

[Fwd: Monroe Re -rating]
Subject: [Fwd: Monroe Re -rating]
From: Michael Parker <[e-mail]>
Date: Wed, 07 Jul 2004 09:40:46 -0400
To: Susan A Wilson <[e-mail]>
Susan,
Sonja has recommended some language (see below) that should be considered for the ATC
you plan to issue to Monroe for their re -rating. It will at least let them know that we are
keenly aware of their capacity problems.
Michael
Sonja Williams wrote:
e'S, '
I think we should include language referencing the .0223(1) and (2) 80% and 90% rule
for future WWTP capacity (Monroe's 2003 calendar year average was 8.03 mgd-89%
capacity). This way Monroe has their warning and would know the Division is aware of
their current status, and the regional office could use this as a lever for moratorium if
capacity becomes an issue.
Michael Parker wrote:
i? %
Per Susan's message below, do either of you think that we need to add anything to the
ATC?
Susan Wilson wrote:
Thanks for the message, Mike. If you guys would like some type of condition/clause
in the ATC let me know (I'm not sure what, if anything, needs to be put in there re.
the pump stations - but if you guys want something in there, we can do that).
Michael Parker wrote:
Susan,
Based your phone conversation with Sonja Williams on 6/30, and my
conversations with Sonja as well as Barbara Sifford who handles
collection system inspections for us, it appears to us that Monroe would
comply with the requirements of 15A NCAC 2H .0219(h)(2) based on our
review of their pumping capacities. It does get a little confusing when
you consider that the above rule is specific towards collection system
pumping stations, and the City is using influent pumps at their WWTP to
help support their case. In any case, it still appears that they have
sufficient (2.5 x design flow) pumping capacity, which should not
negatively affect their request for a re -rating.
If you have any questions, please advise.
Michael
Susan Wilson wrote:
1 of 2 7/7/2004 9:51 AM

[Fwd: Monroe Re -rating]
Mike,
Just sent you a fax of the info Jim Cramer sent me. Just now had a
chance to look at it. Let's talk about it after you receive it (and
after you've had a chance to look at it). Thanks!
Sonja Williams - [e-mail]
[e-mail]
North Carolina Dept. of Environment & Natural Resources
Div. of Water Quality
919 N. Main St.
Mooresville, NC 28115
Ph: 704.663.1699 Fax: [phone]
WWTP Consultant
Michael Parker <[e-mail]>
Environmental Engineer II
NC DENR - Mooresville
Division of Water Quality
2 of 2 7/7/2004 9:51 AM

JUN-23-04 WED 11:54 AM
FAX NO.
P. 01
HAZENAND SAWYER
Environmental Engineers & Scientists
4011 WestChase Blvd
Suite 500
Raleigh, NC 2760i
919.833.7152
Fax [phone]
FAX
COVER SHEET
Date 611.-‘10,1
To: 3,)500,.. \kJ;
Fax No: I
Sent By J..,
This fax contains 2 page(s), including cover sheet.
0 ('HGCNY
1+1
From:
Company
H&S No:
1..1 FOP REVIEW
0 PLEASE COMMENT
Ei PLEASE REPLY
message messa e
• ..__.... 11441E.....6Aft cAttn cish look
• • - • • .• .--. •
If you do not receive all pages or if portions are illegible, please call [phone].
,•r•• Y ••• MY . Vi o•tli•Ir7NY•• n NI 1..S.:.•••.1 MI . r j1,71-1 C Ch.pl‘Luo Nt . VA . A rA 1,010.0an Fi • F.., C•te•Le Fi L • 0,•1 t F1

JUN-23-04 WED 11:54 Aft
11,1
TVIAtrekelpij
i11 fir m ha)
FAX N0.
T'o Pl•w
it -re
°..
F4.41:1
P, 02
4^14 0 za. t...?
f 1"t . "41( °44a .
. . .41J .. ..) • t• 0
•
Li 1.4 4.d,1- Pa wl S ba.1.,;4%
+14) N1vvitbc 1.4bAtTr
4•Zirebt C./0401%20
.. 000
Gyuettli
`LE)S f'.it; n1 (C.uuu*&)
• • (c& ft Glikt :"" .60214
R quAvea . fjevkQ,fi 15�! N ; i c4c. 2.1-1 .07.19 (')(t)71.7. 1.5x 10.4 2
4.0,tra
►1,
s>;

QG
r William G. Ross, Jr., Secretary
- North Carolina Department of Environment and Natural Resources
Water Quality Section/ NPDES Unit
FAX: [phone]
6/28/04
FAX TO: Mike Parker
Re.: Monroe (Inf. pumping capacity)
Michael F. Easley
Governor
Alan W. Klimek, P.E., Director
Division of Water Quality
FAX NUMBER: MRO
FROM: Susan A. Wilson, P.E.4141"fr---
PHONE: [phone], ext. 510
NO. OF PAGES INCLUDING THIS SHEET: 3
Mike,
Check this out — Jim Cramer faxed it to me. Let's discuss after you've taken a look at it. He's counting the 2
existing influent pump stations and the remote one from Union Co.
Susan

tic'
bo.e -144ib
1?ops- 73
44-AJ /
Z.--/f
/7
1/c e F Ai5
/9- /f 200+ 271. Pow 7 &Alri J
t_ - lo4P/2,9-travi-rAgAPT$
b7L-
T5
Zi?c9
2t7 3/
e' /0, / i /'f i/t-LL1
44'6D/U,vL = Z2o
/10pt q,t 1/l5"/ 1494
t...„--fropc /Ai = z 2_0 0*-AL
( 14-5 Lt( fl(51657-- /2.9-77o Am-5 4/o 5 67(4-Lit P'til 771/S Wfru n
(045 2 ‘ (,, A eye 4 - /ko)JTh I y Ft-o )
5b 3 i c,
kita A- (7o `2,
6-5 AA4? 6p )9 41fAl
tp.4- /lob,
(O,sµ�D
MP 0 ?kJ 5' 3 3.5 1 J
' 2 tIJf . Pump s IJ")
Z puinP' �. may)
l5
,5 ( OD, )/ONE Pub 0(J7 of ScfLd(Ct.
tue- r 0 14 t�

,41oAJ 9* A)5
+ 0 sa At5
lePc z_cr-�
4 3 214 tit
Cam ) ,�f.b )4 -
---- 44 Akc
jt 0, At5
4 .7 3 4(4
7 3 AA a kr. 7 kr
A9, ei-we,P)
/o,74j-
fi&
/3-(tee t Dif uS&S
? 1 i t 306 5
,huge Ss/ avr- pm_ Z' CL.
5A 17- rZ =�-�z.s�
5-47 r' 1Z 6A-e4
e-
4,4JA4-
*VG
rite L&/0-rz
44/4 . dtr w ;;:'
l o 4 n (0 5-' cPb 3-4/5 4
FT Z
/24A'CS
3(42)((O
1v�4r5 5,5c-rk5 (v-15.
J
I 37+ Tito
�.:r-Z

/oP5
, 2L
2)4_150
LL141f. 306
•
• , : , ; , , , , ; ,
. __• : , , ,
, 1 ,
, , • , , , ; , , ; i A
I !
1 ,
H .613 CZ 3S3
-- i
3 i
; 1
- 7,484'11" I : , ' ! i ! i
! !
, ! ;
! i !
3 2 e ao tp,-,_. -1 /
2 1 6'4v croi
.eLiehzetext,
1
! I
! I I
! I

IlloA) gave,
— Z Pa/¼1/4 570(7e
3 Pao( -e-yq-c4.1
0^16
(A) /.61-7-,S 4,4-774Jc 00c- eliCtt
7-672-(/ F/L.--76?-5
0414- fite, 14- f/z-77:4'g-
Akg,1)'4 Pa-,774 •32
u144-1 5Lect./2....
(aif Do) 2_sego Fr'
/0) 400/ 000 1).p
2Seo
Ok--
ejkotivu e04)771_0-
a. 441
-7 aZOi 000 cit- ZAr 66°x!tV fitid Ofr-
70(400) 000 5/4t-/PAy /PAY 4(
2o /
ct)
t_cri /71/2_ Z,
/Lr
6,o A,' AJ
Ti/Pre4t, 515±Al
1 a
Zg°e- M4,
yrt:As vd,xvo
trid7-(c (e)
5€14-
(1(rft04A0 eq )11 I
ihyAlor
s OF Pli-n-y 0414465/kaftralt-y re,a_ goo:5_ a5,
TSS ( - /e ,t) Aiii/ 3-4 z, 0 ,c)
( ear 71191 /5 3, 3A) (far *,,d/ Pit-e 76
WAY Lou/ Auo/N/PFLY *1,55.
60145 Poitt45 C etc &NP44.- *PAR_ 200 3 64i*r- yefriz-)
iyfriecsr
Dv Ati5 2,6

�d,vg
on/ A' nl S �` J tt /ZA,G AA, cf /1 5 (3 / /
�n1 I6 tl&Jr Pl/M P Sri97-72/J 5 it 2• 'TIED i �� � f i_ uv ` Ai/ S
SD 1_0c* 4 r ;Wow ON tJ ovcyLect_
Looe-(i yQ ? /iJ ft u6N% PaM f~ S%f}T/o i `4'A/
CV62,4u, ti7 /iy
# 1 Pe? P 5.77,47 ¢ s.0 c
2 f/JF- Pudgy 5r1177oA/ 2 ® �
2i) •o1f¢(4j( )
/niS AA-rc PF oar- OF S i/e6
7t)E
/L C
/4- 4/cD
13 ✓tA
2? M4v 64/74z./
Pc", /N /NT, AT/0/tl .2is rti6A 21 35 = Z3SAt5-D
Puke /N (/P Si43 # 2 /S
23 y G 26 4.c��
eu r (5a No7 aL-)
2c,5 v
zo,5 ✓_ e 26,
5o NOT 2s'`)
ID r`1 74641-r1 I'oL- M.i . " 4. 7 3 ,+ex
/sue
C�C/tc.�JT 1 'jrN71 c/a 774iE ' � ? , 2t(
Pam-- G)0G tcAd.F.Nr
!NF p ,t P5
(-37b7)4-)
[.4 ST yc-E-A-z-)
4 C 4 4, 4v = /& ^t o
�PlGi (-4 Ai F)JM,z) 9 4��

{'1
I
!
-
�
� i
I
5
-
®
AO
I
I
404,3
i_
.
(D.
'
ci---
i
II
1
I
'
l_ l - -
I
I �
I
-- -
-_ _ _
__
_-
-
-
_--
1 __.
•
j
��I
'
I
i
I
!
- -�-
j
f
Ii
!
I.
!
_

i/14/98 2 25pm FILL
l
PIINFLUENT
PUMPING
STATIONS (2)
,0201\FIGURES\30201-003 by PILL XREFs=00\sp-sc-arn dwg,
COUNTY FLOW
METER (1)
CITY FLOW
ME1ERS
(3)
CENTRA I E
ksk
AAP
FLOW
EQUALIZATION
BASIN
(1)
FILTER BACKWASH RETURN
ROTARY
SCREENS
(2)
AERATION BASIN
SPLITTER BOX
SUPERNATANT
r
AEROBIC
DIGESTER/
THICKENERS
NO. 3&4
r
WAS
-I
AERATION
BASINS
(5)
RAS
J.
IIAZENAND SAWYER
Environmental Engineer° & Scientists
AEROBIC
DIGESTER/
STORAGE
TANK NO 2
T
L. —
CENTRIFUGES
(2)
SAND
DRYING
BEDS
(BACKUP)
SECONDARY
CLARIFIERS
(4)
RAS PUMPING
STATIONS
(2)
J
AEROBIC
DIGESTER/
STORAGE
TANK NO 5
TRUCK
LOADING
PUMP
LAND
APPL.ICA LION
1
LAND
APPLICATION
ri
LEGEND
lIl
TERTIARY
FILTERS
(6)
PUMPS
WAS; ftW.ATER FLOW
- - SOLIDS 11.0W
FILTER
BACK WASII
F' -r
CHLORINE
C0111AC1
TANKS (2)
11OW
t.1EASUREMEN1
CASCAFDE
A[RA
EFI-EUFtir TO
RICIIARDS0I1 CREEK
CL 2
C
S02
I.1F'lti
MONROE WASTEWATER TREATMENT PLANT
MONROE, NOR11-I CAROLINA
EXISTING PLANT
PROCESS FLOW SCHEMATIC

00 AI jla•S
(0 0
9/03
pt col
3‘; ("4:1)
�- 15 5
/,7 (,$)
( �x
1
C$q/ (,G(3.1)
(.2 (3.0)
-- ZtyK
4.I Ci.es) oil (1,$)
2,6 4-z) b.9 (3.0)
4, IS (8. 0)2,,,
7(0
6(03
2.9 0.67)2.2
2.R' (¢.31)
'C,Cfild._;)
1,2 (7,o3).
Q. i3 L2.3,G)
4.9s (6.77)
4,4'3 (/,42)11,
($.13)1,4_
S (q.25)Z.b,
3.64 (5-4, \ ,
(4t4.- f)
:si)
.14
O, '7 (i.)
Z.1 (4,
1c1x
2- (20)
347(I)
2. e
23ST
2 ; o 7 (4-.7)2.3x 60
377
303
Z25,�
32 q, ,63
336
21&,
279
Zoa
2g2
1,7(31
Z3�
114-F 155
2iS
l So
Zoo
(5Z
Joe
[97
Z97
12.e/
o'a6 ( 1 1J
g.
elaa
67.7.5 (`I)
L®,97Z.
(zazi
;
20X

t 4ot
& (1414 -e9r)
3.57 (6.79
Wot
4'732- (,;- .07)
SLo-e-
rt,1r
0,1 ( 1.5) (3,,
(47c ir
14(
9/0 (1 96) 2),
-7(.i 2,01( 3,1) t,c,„
6(0
5(01
(7c
(1.1F aeDD.5-j ( NIP' 'FS S wo41 l3 (fril/)
115-
30 3
'328
(2,6) ,c Z-31
0.7(/,8)
' ( 2.0 2,314
4,6,(719) /6x
l'g
td..0( 4.1)1,8x
.637 (5 i'S) 2,
t8t-Cg(c'4641
I3‘3). Chele40
3(oi
401
\ /0 1
3,9 (1) x
22.57 ( (,;71) 71;,6
2ic (4
23'7
27e7
.307
3z1-
275-
3S-8
257
2.6
.7
542-(. ) s
S, (r0.6.z
207
20
117
207
237
i271
267
2-5 (
;3
S,71
t.
S.7,7
,03
C.07
5, 61
C. PI
6, 7
2,0(

HAZEN AND SAWYER
Environmental Engineers & Scientists
March 16, 2004
Ms. Susan Wilson
North Carolina Department of Environment
and Natural Resources
Water Quality Section
1617 Mail Service Center
Raleigh, North Carolina 27699-1617
Dear Ms. Wilson:
A1-0 fr3 ' FOR— (0 • M
00 7. 3”/4 01 Hazen and Sawyer, P.C.
4011 WestChase Blvd.
Raleigh, NC 27607
919 833-7152
Fax: [phone]
7.1
.71
MAR 1 9 2004
Re: Process and Hydraulic Rerating Evaluation
Expansion from 9 mgd to 10.4 mgd
Permit No. NC 0024333
Thank you for meeting to discuss rerating of the Monroe WWTP. This letter is to provide additional
information on concerns regarding aeration tank retention times and secondary clarifier overflow rates
at the expanded flow. Information is provided on nitrification process evaluations at Monroe, aeration
tank retention times and overflow rates at similar facilities, and performance history at the Monroe
Plant.
Influent pump capacities were reviewed with the City. Four of the influent pumps were rebuilt last year
and provide a capacity of 4 mgd each. The two larger pumps are rated at 7 mgd each, but Kim
reports that the pump delivers 9 mgd when operating in parallel with the 4 mgd pumps under high
flow conditions (maximum wet well level). The firm peak pump capacity from Union County is
2.6 mgd. Assuming that the large pump is rated at 9 mgd, then the firm capacity of influent pumps at
the Monroe Plant is 27.6 mgd or 2.65 times 10.4 mgd.
Process Design Model for Nitrification
Hazen and Sawyer has used the nitrification process design model from the EPA Process Design
Manual for Nitrogen Control since 1978 for the evaluation and design of nitrification at wastewater
plants (See attached). The model was confirmed by nitrification performance at the North Buffalo
Creek Plant in Greensboro through the 1980's and at the Osborne Plant in Greensboro in 1994. A
yield coefficient of 0.65 and a decay coefficient of 0.05 are used in the model. A safety factor >_ 1.0
is required to maintain nitrification performance.
The process design model for nitrification was used to evaluate aeration tank requirements at the
Monroe WWTP. Operating data from February 2003 were used to "back -calculate" the actual
process model safety factor. Input data to the process model included operating data as follows:
Wilson 03.16.04 Itr
New York. NY • Philadelphia, PA • Detroit, MI • Raleigh, NC • Charlotte, NC • Greensboro, NC • Atlanta, GA • Fairfax, VA • Baltimore. MD • Hollywood, FL • Baca Ratan, FL • Fort Pierce, FL • Sarasota. FL • Miami. FL

HAZEN AND SAWYER
Ms. Susan Wilson
March 16, 2004
Page 2
Flow, mgd 10.4
Minimum wastewater temperature, °C 12.6 °C
Effluent pH 6.6
Influent BOD, mg/l 282
MLVSS, mg/I 2880
The minimum hydraulic retention time (HRT) for nitrification per the process design model for February
2003 was calculated to be 9.4 hours. In February 2003, the actual hydraulic retention time at
10.4 mgd was 10.9 hours, which corresponds to a process safety factor of 1.26. Plant performance
in February 2003 at the Monroe Plant (effluent BOD < 5 mg/I; effluent NH3-N=0) indicates a stable
and effective nitrification process corresponding to operation well above the minimum solids retention
time required for nitrification.
Nitrification Models and HRT's at other WVVTP's in North Carolina
Hazen and Sawyer has used the nitrification process design model from the Nitrogen Control Manual
to design activated sludge facilities at several plants in North Carolina. A partial listing of plants and
HRT's provided for nitrification (and BNR) based on the model are as follows:
HRT for Nitrification HRT for BNR
Plant/Location (hrs) (hrs)
Neuse River Plant — Raleigh, NC 9.7
North Buffalo Creek Plant — Greensboro, NC 6.5
T.Z. Osborne Plant — Greensboro, NC 16.1
Eastside Plant — High Point, NC 4.6
Monroe Plant — Monroe, NC 10.9
Big Buffalo Plant — Sanford, NC 26.3
North Durham Plant — Durham, NC 9.8
South Durham Plant — Durham, NC 12.8
15.4
N/A
N/A
N/A
N/A
22.8
22.4
All HRT's are calculated based on permitted capacity. The hydraulic retention times vary over a wide
range depending on the BOD loading at each plant and process safety factor provided. All of the
above process designs for nitrification and BNR have been accepted by DWQ. The proposed HRT for
nitrification in Monroe of 10.9 hours at 10.4 mgd is within the range of HRT's normally provided for
nitrification at similar plants in North Carolina.
Wilson 03.16.04 Or

HAZENAND SAWYER
Ms. Susan Wilson
March 16, 2004
Page 3
Secondary Clarifier Overflow Rates at Other WWTP's in North Carolina
Secondary clarifiers at the Monroe Plant provide an overflow rate of 458 gpd/ft.2 at 10.4 mgd. The
current and proposed design peak flow capacity of the Monroe Plant is 27.5 mgd or 2.64 times the
proposed permitted capacity of 10.4 mgd. Clarifiers at the Monroe Plant provide an overflow rate of
1211 gpd/ft.2 at the design peak flow of 27.5 mgd.
Overflow rates for secondary clarifiers for the plants listed above are as follows:
Plant/Location
Overflow Rate at Overflow Rate at Peak
Permitted Flow Flow
(gPdlsf) (gpd/sf)
Neuse River Plant — Raleigh, NC 505 1263
North Buffalo Creek Plant — Greensboro, NC 616 1078
T.Z. Osborne Plant — Greensboro, NC 430 1290
Eastside Plant — High Point, NC 393 1181
Monroe Plant — Monroe, NC 458 1211
Big Buffalo Plant — Sanford, NC 399 1198
North Durham Plant — Durham, NC 380 1140
South Durham Plant — Durham, NC 470 1410
The proposed overflow rate at the Monroe Plant at 10.4 mgd is within the range of secondary clarifier
overflow rates normally provided for nitrifying/BNR plants in North Carolina. Secondary clarifiers at
the Monroe Plant are 12 feet deep and have been recently upgraded with new clarifier mechanisms.
Demonstrated Performance at 10.4 mgd
The Monroe Plant has already demonstrated its capacity to treat a monthly average of 10.4 mgd at
design loadings and at a minimum temperature of 12.6°C. Performance of the Monroe Plant in
winter of 2003 confirms that the Plant can be rerated 10.4 mgd.
The Monroe Plant had no effluent violations between August 2002 and July 2003 despite average
wastewater flows of 10.40 mgd, 11.10 mgd, and 10.97 mgd in February, March, and April of 2003.
From a process point of view, the plant was most stressed in February 2003 when the wastewater
temperature was 12.6°C. BOD loadings in February 2003 were 24,460 Ibs/day compared to an
average annual loading of 20,020 Ibs/day. BOD loadings were slightly higher in April 2003 (25,526
Ibs/day).
Wilson 03.16.04 hr

HAZEN AND SAWYER
Ms. Susan Wilson
March 16, 2004
Page 4
Effluent ammonia concentrations of 0 mg/I were reported in February 2003 and April 2003 indicating
that consistent, stable nitrification was achieved through the period. Nitrification performance was
maintained through an extended period of high organic loadings, high flows, and cold wastewater
temperatures. Nitrification performance was maintained, not just for a random month, but under
proposed design conditions at the rerated flow of 10.4 mgd. (i.e., maximum month BOD loadings,
minimum wastewater temperature.) Without this record of performance, the request to rerate Monroe
Plant would have relied on predictive process modeling only. Actual performance information from
the Monroe Plant at proposed design conditions provides the best measure of actual plant capacity
and the best technical basis for rerating the Monroe Plant to 10.4 mgd.
Please call if you need additional information or if you would like to meet to discuss.
Very truly yours,
HAZEN AND SAWYER, P.C.
es A. Cramer, P.E.
Vice President
JAC:sra
cc: Russ Colbath
Jim Struve
Wilson 03.16.04 Itr

Pro ass Puy ularw+� ,fire Gw, �-rv� U t P A , ► 9,'� S
Virtually all applications of the high purity oxygen activated sludge process to nitrification
have been for separate stage nitrification applications (Section 4.6), rather than for
combined carbon oxidation -nitrification applications.
4.3.2 Utility of Nitrification Kinetic Theory in Design
The nitrification kinetic theory presented in Chapter 3 may be directly applied to the design
of those activated sludge modifications compatible with nitrification. The equations must be
adapted to the hydraulic configuration under consideration, but in all cases this adaptation
is relatively straightforward.
Nitrification kinetic theory can be very usefully applied to define the following parameters:
1. The safety factor required to handle diurnal transients in loading to prevent
significant ammonia bleedthrough under peak load conditions.
2. The design solids retention time under the most adverse conditions of pH, DO and
temperature.
3. The allowable organic loading on the combined carbon oxidation -nitrification
stage.
4. The required hydraulic detention time in the aeration tank at ADWF.
5. The excess sludge wasting schedule.
The following sections present the design procedures in terms of a number of specific
examples. The procedure developed for each case has often been termed the "solids
retention time" design approach.
4.3.3 Complete Mix Activated Sludge Kinetics
As a design example, consider a l mgd treatment plant that must achieve complete
nitrification at 15 C. The plant incorporates primary treatment. Primary effluent BOD5 is
150 mg/1, including solids handling return streams to the primary. Total Kjeldahl Nitrogen
(TKN) is 25 mg/1 as N. As a simplifying assumption, neglect that portion of the TKN that is
assimilated into biomass or associated with refractory organics. The wastewater has an
alkalinity of 280 mg/1 as CaCO3. The procedure is as follows:
1. Establish the safety factor, SF. The SF is affected by the desired effluent quality.
Assume a minimum SF of 2.5 is required due to transient loading conditions at
this particular plant (see Section 4.3.3.2).
2. Establish the minimum mixed liquor dissolved oxygen (DO) concentration.
4-7

Consideration of aeration efficiency at the peak hourly load is required (see
Section 4.8). Assume a minimum DO of 2.0 mg/1 is selected as a compromise
between power requirements and a consideration of the depressing effects of low
DO levels on the rate of nitrification as discussed in Section 3.2.5.5.
3. Estimate the process operating pH (see Section 4.9.2). Approximately 7.14 mg/1
of alkalinity as CaCO3 is destroyed per mg/1 of NH4. -N oxidized. Neglecting the
incorporation of nitrogen into biomass, the alkalinity remaining after nitrification
will be at least:
280 - [7.14(25)1= 102 mg/I
If a coarse bubble aeration system is chosen, the pH should remain above pH 7.2
and chemical addition is not required for pH control (see Section 4.9.2).
4. Calculate the maximum growth rate of nitrifiers at 15 C, DO = 2 mg/1, and
pH > 7.2. The appropriate equation to be used was presented in Section 3.2.6 and
is as follows:
O r,
;IN = µN(K0'
+DO - 8.33(7.2 - pH)
2
•
where: µ = maximum possible nitrifier growth rate, day-1,
environmental conditions of pH, temperature, and DO,
• maximum nitrifier growth rate, day -I, and
(3-23)
• half -saturation constant for oxygen, mg/1.
The last bracketed term is taken as unity at a pH above 7.2. Using the specific
values adopted in Section 3.2.5 for µN and K02 leads to the following expres-
sion:
"IN 0.47 [o.098(T_ 15)I rD0 +01.3] L - 0.833(7.2 - PH]
JL
Using the numbers given above:
IuN ▪ = (0.47)(0.61) = 0.285 day
(4-1)
5. Calculate the minimum solids retention time for nitrification. From Equation
3-15, the correct expression is:
4-8

where: a m
For this example:
0m_ 1
c pN
(4-2)
= minimum solids retention time, days, for nitrification at pH,
temperature and DO.
Om = = 3.51 days
0.285
6. Calculate the design solids retention time. From Equation 3-29, the correct
expression is:
where: 6
c
For this example:
9c =SF •Om
solids retention time of design, days.
9d = 2.5(3.51) = 8.78 days.
(4-3)
7. Calculate the design nitrifier growth rate. From Equation 3-12, the correct e. -
expression is:
where: µN =
For this example:
nitrifier growth rate Nitrosomonas , day 1.
_ 1
1N 8.78
= 0.114 day1
(4-4)
8. Calculate the half -saturation constant for ammonia oxidation at 15 C. The proper
expression is:
K=100.051T-1.158
N
where: KN = half -saturation constant for NH4 — N, mg/1, and
T = Temperature, C
For this example:
KN = 10 0.393 = 0.405 mg/1
4-9
(3-13)

9. Calculate the steady state ammonia content of the effluent. Equation 3-24 is
directly applicable to complete mix activated sludge systems, where N 1 is the
effluent ammonia -nitrogen content:
• N1
PN µN
KN+N1
where: N1 = effluent NH4 — N, mg/1
For this case:
N1
µN = 0.114 = 0.285
N1 + 0.405
N1=0.27mg/1
(3-24)
Transient loading effects on effluent quality are presented in Section 4.3.3.2.
10. Calculate -the organic removal rate. The design solids retention time applies to
both the nitrifier population and the heterotrophic population. Equation 3-27 can
be applied to determine substrate removal rates:
1
Pb ed Ybgb — Kd
c
(3-27)
where: Yb = heterotrophic yield coefficient, lb VSS grown per lb BOD
removed,
qb
rate of substrate removal, lb BOD5 removed/lb VSS/day, and
Kd = "decay" coefficient, day-1.
Assume representative values for Yb and Kd : 29
Yb = 0.65 lb VSS/lb BOD rem.
Kd = 0.05 day-1
Therefore:
0.114 = 0.65gb — 0.05
qb
0.2521b BOD rem./lb MLVSS/day
4-10

In the above calculation of qb, it is assumed that the fraction of nitrifiers is low
and can be neglected (see Section 4.6.1 for a discussion of this point).
11. Determine the hydraulic detention time at A.DWF. In this analysis, the MLVSS
content and effluent soluble BOD must be known. The effluent soluble BOD5
can be assumed to be very low (say 2 mg/1). The MLVSS content is dependent on
the mixed liquor total suspended solids, which is in turn dependent on the
operation of the nitrification sedimentation tank (Section 4.10). Assume for the
purposes of this example that the design mixed liquor content at 15 C is
2500 mg/1. At a volatile content of 75 percent, the MLVSS is 0.75 (2500) _
1875 mg/1. From Equation 3-28, the expression for hydraulic detention t1.me is:
where:
HS—S
T= o 1
Xigb
HT = hydraulic detention time, days,
X1 = mixed liquor volatile suspended solids, MLVSS, mg/1,
So = influent total BOD5, mg/1, and
S1 = effluent soluble BOD5, mg/1.
For this example, the hydraulic detention time at ADWF is:
HT = 8
252 0.313 days
(1875)(0.)
= 7.5 hours
(4-5 )
12. Determine the organic loading per unit volume. The volume required in the
aeration basin for 1 mgd flow is:
Volume = Q • HT = 1(0.313) = 0.313 mil gal = 41,844 cu ft
where: Q = influent flow rate, mgd
The BOD5 loading is:
(1)(8.33)(150) = 1249 lb/day
4-11

The BOD5 load per 1000 cu ft is:
1249 41.84 = 29.9 lb BOD5/1000 cu ft/day
13. Determine the sludge wasting schedule. Sludge is wasted from the system from
two sources: (1) solids contained in the effluent from the secondary sedimenta-
tion tank, and (2) intentional sludge wasting from the return sludge or mixed
liquor. The sludge to be wasted under steady state conditions can be calculated
from the solids retention time. The total sludge wasted per day is:
S = 8.33(Q . X2 + W • Xw) (4-6)
where: S = total sludge wasted in lb/day,
W = waste sludge flow rate, mgd
X2 = effluent volatile suspended solids, mg/1, and
Xw = waste sludge volatile suspended solids, mg/1
The inventory of sludge in the system is:
where: I
V
I = 8.33(X 1 - V) (4-7)
inventory of VSS under aeration, lb, and
volume of aeration tank, mil gal
The solids retention time is defined as:
ed = 1
c S
In this case, application of Equation 4-7 yields:
(4-8)
I = 8.33(1875)(0.313) = 4889 lb )JSS
Using Equation 4-8 and a design 0c of 8.78 days, the sludge wasted from the
system is:
S = 4889/8.78 = 557 lb/VSS day
4-12

The sludge contained in the effluent at 1 mgd can be calculated assuming that the efflu-
ent volatile suspended solids is equal to 12 mg/1:
8.33 (1) (12) = 100 lb VSS/day
By difference, the lb of MLVSS to be wasted from the mixed liquor or return sludge is:
557 — 100 = 457 lb VSS/day
4.3.3.1 Effect of Temperature and Safety Factor on Design
The design example presented in the previous section provided one solution to a set of
stated conditions. Alteration of the lowest temperature at which nitrification will be
supported, or the design safety factor, or the wastewater strength, or the assumption of
different kinetic constants can materially alter the design.
To give one illustration, Table 4-2 has been prepared using differing safety factors (2.0 to
3.0) and differing minimum wastewater temperatures with design calculations to derive the
computed quantities shown. Assumptions have been made for illustrative purposes as to the
allowable MLSS. Allowable mixed liquor levels are a function of sedimentation tank
operation. The mixed liquor level that can be maintained will be affected by reduced
sedimentation efficiency at lower temperatures. Consideration of aeration tank -secondary
sedimentation tank interactions is presented in Section 4.10.
As can be seen from Table 4-2, low temperature applications (10 C) of combined carbon
oxidation -nitrification in complete mix activated sludge systems require very long hydraulic
residence times to achieve favorable conditions for nitrification. This factor was one of the
reasons for the development of separate stage nitrification systems. As temperatures rise,
required residence times are materially reduced. At 20 C, less than five hours is required for
virtually complete nitrification in the specific case examined. While it is possible to design
for nitrification using the relatively low detention times given in Table 4-2 for 20 C, special
attention must be given to oxygen transfer as a very high oxygen demand is expressed per
unit volume. Considerations for oxygen transfer are given in Section 4.8.
4.3.3.2 Consideration in the Selection of SF
In introducing the safety factor concept to the design of biological treatment systems,
Lawrence and McCarty29 noted that the SF was necessary to achieve high efficiency of
treatment, to insure process stability and to provide resistance to toxic upsets. Excessively
high safety factors resulted in higher operating and capital costs. It was noted that the safety
factor concept had been implicitly incorporated into treatment plant design practice by the
selection of solids retention times in excess of ,0m
c
4-13

TABLE 4-2
CALCULATED DESIGN PARAMETERS FOR A 1 MGD
COMPLETE MIX ACTIVATED SLUDGE PLANT
Minimum
temp. for
nitrification,
C
Maximum
possible
nitrifier
growth rate,
AN , day-1
Assumed
allowable
MLSS/MLVSS
mg/I
Safety
Factor,
SF
Design
solids
retention
time, days
9
Steady
state
effluent
NH+-N,
nlg/1
Organic
removal
rate,
lb BODrem/
lb iVILVS5-day
Hydraulic
retention
time. a
hours
BODE
loading
(volumetric)
lb/ 1000/c[/dayb
2,000
2.0
11.5
0.23
0.21
11.0
20.5
10
0.175
2.5
14.3
0.15
0.19
12. a
17.5
'
1,500
3.0
17.2
0.11
0.17
14.0
15. 8
2,500
2.0
7.0
0.40
0.29
6.4
34.9
15
0.285
2.5
8.8
0. 27
0.25
7.5
29.9
1,875
3.0
10.5
0.20
0. 22
8.5
26.5
3,000
2.0
4.3
0. 73
0.44
4.4
51.5
20
0.465
2.5
5.4
0.49
0.36
5.2
43.0
2,250
3.0
6.4
0.36
0.32
G. 0
37.3
a At ADWF
b 62.4 lb/1000 cf/day = kg/m3/day

Because the SF concept is relatively new, there is no plant scale experience with its
application accumulated as yet on which to base broad recommendations. Rather, kinetic
theory itself is used in this section to establish minimum factors of safety considering the
desired degree of nitrification under steady state and transient load conditions. It must be
emphasized that these are minimum values and individual designs may exceed these values
for a variety of reasons. For instance, the presence of industrial wastes may adversely affect
nitrification rates, requiring conservatism in the selection of the SF.
Figure 4-2 provides a wider array of safety factors for the design example presented in Table
4-2. As may be seen, the selection of the SF has a marked effect on the calculated steady
state values of ammonia in the effluent. If relatively complete nitrification is to be obtained
(at steady-state) resulting in 0.5-2 mg/1 of ammonia nitrogen in the effluent, a minimum SF
of 1.5 is appropriate for application to complete mix activated sludge systems. Further,
effluent values for a comparable plug flow system are also shown in Figure 4-2 (see Section
4.3.5 for plug flow data). As may be seen, complete mix systems have higher effluent
ammonia levels than plug flow systems at the same SF.
In all practical applications, waste treatment plants do not operate at "steady state."
Significant diurnal variation in the nitrogen loading on such systems occurs. Figure 4-3
shows the diurnal variations in influent flow and TKN loading experienced at the Chapel
Hill, N.C. treatment plant. The ratio of the maximum TKN loading to the average was 2.17,
while the ratio of the maximum to minimum was 6.72. The Chapel Hill system is a relatively
small system (1.8 mgd) with high peak to average ratios for all constituents.30 The variation
in load for each community will be a function of the unique characteristics of that
community (see Section 4.8), and data must be individually developed for each situation.
TKN load variations have a significant impact on nitrification kinetics, and ammonia
bleedthrough can occur under peak load situations.31,32 Kinetic theory can be applied to
these situations, however, and the safety factor established at levels which will prevent
ammonia bleedthrough from causing significant deterioration of effluent quality.
A mass balance on nitrogen in the organic and ammonia form can be made at any time
during a diurnal cycle which states that the influent TKN load is equal to the effluent
ammonia load plus that nitrified in the complete -mix reactor during any time, At:
N0QAt = q fX 1 VAt + N 1 QAt (4-9)
where: No = influent TKN concentration, mg/1,
N I = effluent ammonia nitrogen concentration, mg/1,
Q = influent or effluent flow rate, mgd,
At = time increment,
4-15

V = volume of aeration basin, mil gal,
f = nitrifier fraction of the mixed liquor solids
FIGURE 4-2
EFFECT OF THE SAFETY FACTOR ON STEADY STATE EFFLUENT
AMMONIA LEVELS IN SUSPENDED GROWTH SYSTEMS
I
4 --
E
3—
+Nt
2-
1 —
1 1
A. at 20 C
COMPLETE MIX
0 VirPLUG F LOW
I I 1 I l I t 1
1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4
SAFETY FACTOR, SF
2.5
2.6 2.8 3.0
COMPLETE MIX
1 1 1
B. at 10C
0.5 1PLUG
FLOW
0 1 I 1 I 1 1 •I I 1
1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0
SAFETY FACTOR, SF
4-16

PERCENT OF AVERAGE FLOW
PERCENT OF AVERAGE
200
180
160
140
120
100
80
60
40
20
0
220
200
180
160
140
120
100
80
60
40
20
FIGURE 4-3
DIURNAL VARIATIONS AT THE CHAPEL HILL, N.C.
TREATMENT PLANT (AFTER HANSON, ET AL. (30) )
2400 0400 0800 1200
TIME
DIURNAL VARIATION IN WASTEWATER FLOW
24 00 0400 0800 1200
T IME
DIURNAL VARIATION IN NITROGEN LOAD AND CONCENTRATION
4-17
1600
2000
2400
0
1600
2000
2400

This equation neglects synthesis terms, assumes all influent organic N is hydrolyzed, and
neglects terms relating to the rate of change of ammonia concentration in the reactor.
Numerical solution techniques are available to handle transient load effects more exactly.32
Equation 4-9, however, is useful for approximating the effects of transient loads.
Equation 4-9 may be solved for Ni, by substitution for the terns for nitrification rate, qN
and the term fX 1 V, representing the inventory of nitrifying organisms. The inventory of
nitrifying organisms can be related to the solids retention time through the following
equation:
0d = fX1 V _
c Q YN(No - N 1)
where: o = 24 hr-average influent TKN, mg/1
N1 = 24 hr-average effluent NH4 - N, mg/1
Q = mean flow rate (ADWF), mgd, and
YN -- nitrifier yield coefficient, lb VSS/lb NH4+ - N removed.
(4-10)
The term QYN(No-N 1) represents the quantity of nitrifiers grown per day, which must be
wasted each day to establish a steady -stage solids retentiot► time, 0 d The average terms, No
and N1, are flow weighted averages of nitrogen concentration of an entire day (the
equivalent of composite samples). Q represents the average dry weather flow (ADWF).
The nitrification rate from Equations 3-20 and 3-24 is:
/IN Ni
YN KN + N1
Substitution of Equations 4-10, 4-1 1 and Equation 3-29 into Equation 4-9 yields:
Ni
No=(No-N1) NSF +N
Q KN+N1 1
qN
(4-11)
(4-12)
Equation 4-12 can be used to solve for N1 over a 24-hr cycle since all other quantities in
Equation 4-12 are known or can be estimated. Initially, NI
can be estimated to be the
calculated steady-state value. Once Equation 4-12 has been applied to generate a 24-hr cycle
of NI values, a new value of NI may be calculated. If N1 differs significantly from the
initial assumption, the calculation process can be repeated.
4-18

Equation 4-12 has been applied to the variations in load observed at Chapel Hill, and using
the design information used to generate Table 4-2 at a temperature of 15 C. The results of
this analysis are plotted in Figure 4-4 for three different assumed safety factors, 1.5, 2.0,
and 2.5. As may be seen, the assumption of the safety factor has a marked effect on the
average effluent ammonia content, Ni. For this particular case, the ratio of peak to average
TKN loading was 2.2; the SF had to exceed this ratio (2.5) to produce an effluent that had,
on the average, less than 1 mg/1 of ammonia-N.
The application of Equation 4-12 to several other such cases. showed the same effect;
namely, the minimum safety factor should equal or exceed the ratio of peak ammonia load
to average load to prevent high ammonia bleedthrough at peak loads. This statement may be
used as "a rule of thumb" for designing suspended growth nitrification systems operated in
the complete mix mode.
A flow equalization procedure applicable to reducing diurnal peaking on nitrification
systems is presented in Chapter 3 of the Process Design Manual for Upgrading Existing
Wastewater Treatment Plants.25 By incorporating flow equalization into treatment plants,
E
EFFLUENT
20
0
FIGURE 4-4
EFFECT OF SF ON DIURNAL VARIATION IN EFFLUENT AMMONIA
SF=1.5
N i = 5.5
A
SF = 2.5
•
N1=0.6
1
N� = 24 hr average
composite NH4- N
concentration
S F = 2.0
N1 = 1,5
2400
04 00
0800 1200
T!ME, HR
4-19
1600
2000
2400

the safety factor used in kinetic design of the nitrification tanks may be reduced. Case
examples for treatment plants incorporating flow equalization are presented in Sections
9.5.1.1, 9.5.1.2 and 9.5.2.1.
4.3.4 Extended Aeration Activated Sludge Kinetics
The procedure presented in Section 4.3.3 for complete mix activated sludge kinetics is
directly applicable to extended aeration activated sludge. Extended aeration systems are
usually operated at such long solids retention times that except during cold temperatures
(5-10 C) nitrification is usually obtained in properly operated systems.
4.3.5 Conventional Activated Sludge (Plug Flow) Kinetics
The approach for conventional activated sludge plants is similar to that for complete mix
plants with the exception of the equations used to predict effluent quality. The plug flow
model -may be applied to approximate the hydraulic regime in these plants. The Monod
expression for substrate removal rate (Equation 3-24) must be integrated over the period of
time an element of liquid remains in the nitrification tank. The following is a solution for
plug flow kinetics that can be adapted to this. problem as shown:29
µN(No - NI)
No
(No-N1)+KNln N
1
for < 1 (4-13)
where: r = recycle ratio (or return sludge ratio).
or
1
(No - N1)
SF N
(No - N 1) + KN In No
1
for < 1 (4-14)
Equation 4-14 is evaluated in Figure 4-2 for the design example presented in Section 4.3.3.
Comparing the safety factor to the safety factor producing the same effluent ammonia in
the complete mix case, it can be seen that lower values of the SF are required for plug flow
nitrification processes than for complete mix nitrification processes. This means that plug
flow processes theoretically can be more efficient at the same SF, or alternatively, require
less aeration tank volume for the same level of nitrification efficiency. However, plug flow
type reactors have the disadvantage that the carbonaceous oxygen demand is concentrated
at the head end of the tank, making it difficult to supply enough air in that area for both
carbonaceous oxidation and nitrification. Air diffusion systems must be specifically
designed to handle this concentrated load. Otherwise, the first portion of the tank will not
be available for nitrification and thus effective volume for nitrification will be reduced.
4-20

3Pof
C' M9N y61-49
fit- 0rttl
,'
(e" e9(-41v5 -1-b (1)
0l41) somf Te) p'.4, 7515 ,y f 2-., S4.yt))
�H A-u = W/ ,4 / (Ste _ (ate& tow- Ail 1,-e .dgq
Cov,,/ceniv 4vu-- P D?,L- IN,C61 655 (Api O L/ J
tVota4-3(01v)
5wvg (z. s ip
w6v7- pcocuAl
5 D&A/ ' c,1 w5 t Low 5 w/
tfez-rAAA! 5,
J '5 baeuti 200 3 r nt/'
jbty f ,Mi l �+v� .r 4) 4. 4 emu- TO Ho. l5fece5.
AuW-01414
w /41ttPi2- — G /t 2
�.WtoN 6.
4/fro/I Go • (5. Ce,/ fR rfAi 46Nicy
w4ptiea-erz-- )
/eou ry 7y I _
() z P41.6
coo NTY glow
Deno- Ev e-- D ffAJ / i J WA2 Z t (Ai e3%`siet)

J1AVAk onl-ff%
j U 1A( moo GAgon/ 64✓ Win— i✓g)
Alf
1/114!d 1456 /I4wo Mf)((Avvvq g dv 5 )
arq„..?-4e/7)
W rtr C((i,i
W Pctottp� �foJJS
4-
ftetiq /G ppg cc'
(4 5161045 4125o L
r 76-
1foAi t3 S(iv
. 5 6frvp___
lit 5 Q0,„,i
&Li& tto-D 7711S tAl 7-get R4-57- AGIVre-,
72, ao uJ y,JAJ 4 Lo i2�

HAZEN AND SAWYER
Environmental Engineers & Scientists
November 21, 2003
Ms. Susan Wilson
North Carolina Department of Environment
and Natural Resources
Water Quality Section
1617 Mail Service Center
Raleigh, North Carolina 27699-1617
Dear Ms. Wilson:
Hazen and Sawyer, P.C.
4011 WestChase Blvd.
Raleigh, NC 27607
919 833.7152
Fax: [phone]
o2g1.7115kol
Re: Process and Hydraulic Rerating Evaluation
Monroe WWTP Interim
Expansion from 9 MGD to 10.4 MGD
Permit No. NC0024333
We are submitting three (3) copies of the "Process and Hydraulic Rerating Evaluation" for the
Monroe WWTP. The evaluation was referenced in Russ Colbath's letter dated October 29
concerning rerating of the Monroe WWTP from 9 mgd to 10.4 mgd. The evaluation 'confirms
that the Monroe Plant can be rerated to 10.4 mgd without construction of new facilities.
Although not required for rerating to 10.4 mgd, the City is planning to expand the existing
flow equalization basin and make filter improvements in 2004 that will provide additional
process safety factor and improved performance especially during extreme wet weather.
Please call if you need any additional information.
Very truly yours,
HAZEN AND SAWYER, P.C.
CA.,,
es A. Cramer, P.E.
Vice President
JAC:sra
Enclosures
cc: Rex Gleason, NCDENR, Mooresville Regional Office
Kim Hinson, WWTP Superintendent
Russ Colbath, Director of Water Resources
Jim Struve Hazen and Sawyer Engineers
Wasan 1120.03'.tr
• + n • r , :' c ,: t • r;. h.ac'ei;.t r, P4
hs.v YO'R, .1`' • „Rr,JCE, 'iV• NOOdta:'j� �Y • D4UGI: b+ - nri�C�. :i. •. n3i;rt�?. H: • at ant: �? • f;,,rfa,, LA • ti�+t��t�b0� Fl • eJ"3 yZL?n . � • f yr P:.'C,,. i•i. • .,. a. ti d. L •' S:'s. „ • c

City of Monroe
North Carolina
Process and Hydraulic Rerating Evaluation
Monroe Wastewater Treatment Plant
Interim Expansion from 9 MGD to 10.4 MGD
November 2003
HAZEN AND SAWYER
Environmental Engineers & Scientists
30202-001-SL-01.cdr

PROCESS AND HYDRAULIC RERATING EVALUATION
MONROE WWTP INTERIM EXPANSION
FROM 9 MGD TO 10.4 MGD
1.0 Background Information
The Monroe Wastewater Treatment Plant has a permitted capacity of 9 mgd and serves the City of Monroe, Town of
Wingate, Town of Marshville, and portions of Union County. The Monroe WWTP discharges to Richardson Creek, a
tributary of Rocky River in the PeeDee River basin.
The original plant was constructed in 1965 with a design capacity of 3.5 mgd. The Plant was expanded to 7.0 mgd in
1976 and 9.0 mgd in 1995. Solids handling improvements including a 3.0 MG solids storage tank were constructed
in 1997, and 2 MG of flow equalization capacity was added in 1998.
The Monroe Wastewater Treatment Plant operates under NPDES Permit No. NC0024333 with the following monthly
limits:
Flow, mgd
BOD (Summer), mg/I
BOD (Winter), mg/I
NH3-N (Summer), mg/I
NH3-N (Winter), mg/I
TSS, mgil
9
7.3
14.5
1.0
2.0
30.0
The permit is effective through January 31, 2004. The renewal application is currently pending.
The NPDES permit for the Monroe Wastewater Treatment Plant also includes limits at 12.5 mgd. A 201 Amendment,
Environmental Assessment, and Plans and Specifications were completed in 2000 for expanding the plant to 12.5
mgd capacity. The expansion project was shelved in December 2000 due to decreasing flows and based on
Marshville's intention of constructing a separate plant using the Schaefer process.
Although industrial flows and wastewater strength at the Monroe WWTP have declined since 2000, abundant rainfall
in 2003 and continued wastewater flow from Marshville will result in an average flow in 2003 that will exceed 90% of
the plant's rate capacity (9.0 mgd x 0.9 = 8.1 mgd). Declining influent BOD concentrations allow for increasing the
rated flow of the plant based on the organic loading capacity of the Plant. Hazen and Sawyer has completed a
review of actual plant performance and process and hydraulic capacities confirming that the Monroe WWTP can be
1

rerated from the current permitted capacity of 9 mgd to 10.4 mgd. The review includes an evaluation of the capacity
of each of the unit processes at the Monroe WWTP at a permitted capacity of 10.4 mgd.
2.0 Current Flows, Wastewater Characteristics, and Plant Performance
Flows and wastewater characteristics for the period August 2002 to July 2003 were used to evaluate current loadings
and plant performance. Data for the period are summarized as follows:
7/03
6/03
5/03
4/03
3/03
7.76
8.44
8.86
10.97
11.10
2/03 10.40
1/03 6.76
12/02 8.29
11/02 7.74
10/02 7.18
9/02 6.09
8/02 5.74
Average 8.28
s/da
325 21,033
338 23,792
296 21,872
279 25,526
202 18,700
282 24,460
360 20,296
329 22,747
236 15,234
261 15,629
294 14,932
280 13,404
290 20,020
181 11,714
191 13,444 21.9
196 14,483 19.6
152 13,906 16.3
148 13,701 14.9
197 17,087 12.6
297 16,744 13.6
246 17,008 14.4
178 11,490 17.9
196 11,737 21.3
224 11,377 23.8
249 11,920 25.0
205 14,156 18.7
23.6
Note that the average flow for the period was 8.28 mgd which is 92% of the rated capacity of 9 mgd reflecting the
impact of wet weather on average flows at the plant.
-,� "*-
The average influent BOD for the period of 290 mg/I is wn from an average BOD of 347 mg/I in/'1996-97. BOD
concentrations have declined approximately- ° since 1996-1997 due to reduced number of industries and
implementation of surcharges and improved pretreatment by the remaining industries.
The maximum month average flow and BOD loading during the period August 2002 to July 2003 was 10.97 mgd and
25,526 Ibs/day in April 2003. The plant was most stressed from a process perspective during the month with the 3
(imit coldest wastewater temperature, i.e., February 2003 when the wastewater temperature was 12.6°C. The average
flow and BOD loading in February 2003 was 10.4 mgd and 24,460 Ibs/day.
2

The Monroe WWTP met all permit requirements in both February and April 2003 demonstrating that the Plant is
capable of treating these flows and loadings. Effluent ammonia concentrations of 0 mg/I (as reported) in both months
indicates that consistent, stable nitrification was achieved through the period. Effluent TSS and BOD concentrations
averaged less than 5 mg/l in both months. The performance of the Monroe WWTP during February and April of 2003
at flows of 10.4 mgd and 10.97 mgd confirms that the Plant is capable of meeting limits at a permitted flow of 10.4
mgd. The City plans to add equalization basin volume and make improvements to the existing effluent filters in 2004
that will provide additional wet weather flow capacity and improved effluent quality for a rerated flow of 10.4 mgd.,
3.0 Hydraulic Capacity Evaluation =',-) £�
The design peak flow capacity of the Monroe WWTP is 27.5 mgd. Peak flows at the Monroe WWT occur during wet
weather. The City of Monroe has installed parallel interceptors, replaced damaged sewer lines, and has operated the
Wastewater Treatment Plant to reduce sanitary sewer overflows and to improve treatment performance through wet
weather events. No additional peak flow capacity is being requested or is required as part of the proposed rerating to
10.4 mgd.
Monroe reports effluent flow which includes the effect of equalizing influent flow. Maximum daily average flows since
January 2002 are summarized as follows:
Maximum Daily Average Flows
2002 2003
(mgd) (mgd)
January 13.07 11.87
February 12.64 15.70
March 9.87 \);1 ; 20.94 I'
i
April 10.16 to,°17: 28.27
May 6.64 -7,'I, 17.25
June 9.38 Qb.ck4. :15.41
July 6.90 1I.1(15.31
August 9.83 N/A
September 9.07 N/A
October 12.59 N/A
November -1,'i ; 14.58 1.\ N/A
December " . ` 13.20 I.k, N/A
3

Maximum daily average flows were much greater in wet -year 2003 than in drought -year 2002. Note that the Plant
treated a maximum flow of 28.27 mgd in April 2003. On the day that the plant treated 28.27 mgd, reported effluent
BOD, TSS, and NH3-N concentrations were 6.8 mg/I, 2.6 mg/I, and < 1 mg.!I, respectively. The Monroe WWTP has
recently demonstrated the capability of treating peak wet weather flows and maintaining compliance with all weekly
and monthly effluent limits.
7 o%
Flow equalization of raw wastewater is provided in a 6.3 million gallon lined equalization basin. Influent pumps) 11% N =i
deliver flow either to the existing screenings facility or to the flow equalization basin. A separate pump station is used 7i
to return equalized wastewater to the aeration basin splitter box. ,F1,'
Flow equalization has been an important part of Monroe's wet weather treatment strategy to minimize overflows and
maintain treatment performance. While the existing equalization basin has been effective in limiting peak flows and
maintaining permit compliance, additional flow equalization basin volume will provide greater safety factor for
equalizing extreme wet weather flows. The City is proposing to expand the existing equalization basin by as much as
2 MG depending on final site layout and subsurface conditions. The capacity of the Monroe Plant to treat peak wet
weather flows will be enhanced by the added equalization volume.
4.0 Process Evaluation at Permitted Capacity of 10.4 mgd
A description of existing facilities at the Monroe WWTP was provided in the June, 1999 201 Facilities Plan
Amendment. The 201 Amendment was based on an expansion to 12.5 mgd. A process flow schematic for the
existing plant is shown in Figure 1, The process and hydraulic capacities of existing facilities at the Monroe Plant for
the proposed rerating to 10.4 mgd are presented in the paragraphs below. Design data for the Plant at 10.4 mgd is
provided in Table 1.
4.1 Influent Pumps
Raw wastewater enters the two influent pump stations through the 54-inch and 30-inch Richardson Creek
interceptors. Pump Station No. 1 includes four influent pumps, one variable speed pump and three constant speed
pumps, each with a capacity of 3.5 mgd. Pump Station No. 2 includes two variable speed pumps, with space for two
additional pumps. Each of the two pumps has a capacity of 6.5 mgd. The firm capacity of the combined stations is
20.5 mgd, including five pumps operating together and one of the larger 6.5 mgd pumps out of service.
Total capacity of the influent pumps is 26.5 mgd. Flow from Wingate, Marshville, and Union County is pumped
directly to the Preliminary Treatment Facilities.
Influent pumps are sufficient for projected peak flows at a permitted capacity of 10.4 mgd. No additional influent
pumps are needed for rerating to 10.4 mgd.
-Po Poi
4
�.G \opt
�5�''"" , a .0
4

4.2 Preliminary Treatment Facilities
Raw wastewater from the three force mains from the influent pump stations and the County force main is combined
before flowing to the Screening Building. Incoming wastewater flows through the two rotary screens, which remove
solids which will not pass through the 0.06-inch screen openings. Rotation of the cylindrical screens directs the
captured screenings to screws conveyors, which then carry the solids to the screenings dumpster. Screenings are
disposed of at the BFI Landfill in Charlotte, North Carolina.
Screened flow may be diverted to the flow equalization basin or flow directly to the aeration basin splitter box. The
screens have performed well even at peak flows. The screens are in good condition and the plant staff reports good
operating experience and limited maintenance requirements. Existing screens are adequate for the proposed
permitted capacity of 10.4 mgd.
4.3 Activated Sludge Facilities
.Mix
t"Lvt.JS
Atm 6y PAs
ScR���fS
Screened wastewater, including return flows from the flow equalization basin, is distributed to five aeration basins•
through the aeration basin splitter box. Aeration Basins No. 1 through 4 each have a volume of 0.86 million gallons,
and Aeration Basin No. 5 has a volume of 1.29 million gallons. The total aeration basin volume is 4.74 million
gallons. Aeration basin effluent flows into effluent boxes and is then conveyed to a secondary clarifier_diakibutior�
box. 417 '(+
Airflow to the aeration basins is provided by three blowers in the Blower Building. Two drop legs in each basin
convey the airflow to fine bubble diffusers mounted on the floor of the basin. Aeration basins No. 1 through 4 each
have 1,060 diffusers and Aeration Basin No. 5 has 1,610 diffusers.
Four 85-foot diameter secondary clarifiers are provided for settling of the activated sludge. Each clarifier is of the
center feed, peripheral overflow -type, with suction -type solids collection and removal.
Two return activated sludge (RAS) pumping stations are provided, one for each pair of secondary clarifiers. The
pump stations convey settled solids and scum from the secondary clarifiers to the aeration basin splitter box. Each
station includes three pumps, which may be operated continuously or intermittently based on timers. The two RAS
pump stations have a combined firm pumping capacity of 11.75 mgd, or approximately 113 percent of plant design
flow. The RAS pump stations are also used for wasting activated sludge to the aerobic digesters.
Retention time in the aeration basins to provide compliance with effluent ammonia limits is a function of the organic
(BOD) loading. Because of lower influent BOD concentrations (current average = 290 mg/I) the Plant is capable of
treating higher flow rates today than in 1996-97 when the influent BOD averaged 347 mg/I.
5

The process design for nitrification was evaluated based on wast ater temperatures and concentrations from
February, 2003 when average wastewater temperature was 12�_and the plant was operating at MLVSS/MLSS
concentrations of 2880 mg/l/3932 mg/I. Under these conditions, the nitrification process model used by Hazen and3
Sawyer indicates that 4.07 MG of aeration tank volume is required,at 10.4 mgd. The existing tanks provide 4.74 MG 2
of volume which translates to a process safety factor for nitrification of 1.26 based on the design influent BOD
concentration of 282 mg/I. Solids concentrations can be as low as 2473 mg/I/3376 mg/I for MLVSS/MLSS and still t prc
meet ammonia limits according to the process model. �� � = qwf'
v
Performance in February 2003 confirms that the Plant can meet NPDES limits at design loadings f 10.4 mgd and 1-
282 mg/I BOD (24,460 Ibs BOD/day). The Plant reported an effluent ammonia concentration o 0.00 mg/I and
effluent BOD of less than 5 mg/I in February 2003 which reflect the relatively high process safety factor for
nitrification, even at the rerated flow of 10.4 mgd.
s Co •
The secondary clarifier overflow rate at 10.4 mgd'is 458 gpd/sf, filch is within the range of accepted overflow rates �,\
for nitrifying activated sludge plants. The existing\firm RAS mp capacity of 11.75 m:::;
d exceeds the State's criteria
of providing RAS pumps with a firm capacity of 100% of the design flow of 10.4 mgd.
4.4 Tertiary Filters
45 uJdidoht
Six dual media tertiary filters with air scour are provided for final effluent polishing following the secondary clarifiers.
Each filter has a total media depth of 36 inches, and is 24 feet long by 20 feet wide. At the design flow of 10.4 mgd,
the filters have a hydraulic loading rate of 2.51 gpm/ft2. Filter backwash is pumped from the influent end of the
chlorine contact tanks by two filter backwash supply pumps. Two separate vertical turbine filter backwash waste
pumps are used to convey filter backwash wastewater to the flow equalization basin for return at a controlled rate to
the aeration basin splitter box.
Filters have performed well in polishing the effluent and in maintaining effluent quality through peak wet weather
events. Improvements to the effluent filters are proposed in 2004 that will improve the hydraulic capacity and
performance of the filters including replacement of the existing dual media with a single media with an effective size
of more than 2 mm. Improvements to the effluent filters will result in better effluent quality during wet weather events
and more efficient filter operation over the full range of flows.
4.5 Disinfection Facilities
ott--
Chlorination facilities are located in the Chlorine Building and consist of two wall -mounted chlorinators, each with a
capacity of 500 pounds per day. A covered storage area next to the building has space for chlorine storage. The
duty chlorinator is flow -paced and conveys chlorine gas at a controlled rate to an injector, where the chlorine is mixed p(L
with water then conveyed as chlorine solution to the chlorine contact tanks. -�
6

the contact tanks is approximately 31 minutes at the plant design flow of 10.4 mgd.
Filtered effluent enters the chlorine contact tanks through a 30-inch pipeline to an influent chamber that serves as a
wet well for the filter backwash supply pumps and as the chlorine feed point. Chlorinated wastewater flows through
the two parallel contact tanks, which have a total volume of approximately 0.22 million gallons_ The detention time in
15 o of `
p,UM�
Dechiorination facilities are located in the Sulfur Dioxide Building. Two (1)-ton containers are located outside on a
covered concrete pad. One room in the Sulfur Dioxide Building contains the two wall -mounted vacuum regulators. A
second room contains two wall -mounted sulfonators, each with a capacity of 200 pounds per day, and two sulfur
dioxide injectors. Sulfur dioxide solution is mixed with the plant effluent flow at the chlorine contact tank effluent box.
The plant effluent flow is discharged to the effluent box over a rectangular weir at the effluent end of each contact
tank.
4.6 Aerobic Digesters/Thickeners/Storage Tanks
Five aerobic digesters/thickeners/storage tanks are provided for thickening, stabilization, and storage of waste
activated sludge. The aerobic digesters provide stabilization and volume reduction by destruction of volatile solids
and decanting. Decant water is conveyed by gravity to Influent Pump Station No. 1 for return to the liquid treatment
process.
Waste activated sludge is pumped from the RAS pump stations to Digesters No. 3 and 4, which are currently being
r used for thickening. Solids concentrations as high as 6 to 8 percent are achieved in Digesters No. 3 and 4 by
decanting. Thickened solids from Digesters No. 3 and 4 are conveyed to the centrifuges and Digester/Storage Tanks
No 1, 2 and 5 for additional stabilization and solids concentration.
Aerobic Digester/Storage Tank No. 1 has a diameter of 80 feetand a volume of 0.49 million gallons.
Digester/Storage Tank No. 2 has a diameter of 115 feet and a volume of 1.15 million gallons. DigesterfThickeners
No. 3 and 4 each have a diameter of 65 feet and a volume of 0.25 million gallons. Digester/Storage Tank No. 5 has a
diameter of 140 feet and a volume of 3.0 million gallons. The total volume of all digesters is approximately 5.14
million gallons.
Except for Digester/Storage Tank No. 5, the aerobic digesters/thickeners/storage tanks are mixed and aerated using
surface mechanical aerators, supplemented in Digester/Storage Tanks No. 1 and 2 by surface mixers.
Digester/Storage Tank No. 1 has one 40-HP and two 7.5-HP mixers and two 7.5-HP aerators. Digester/Storage
Tank No. 2 has three 40-HP aerators and one 40 HP mixer. Digester/Storage Tanks No. 3 and 4 each have one 30-
HP aerator. Two 200-HP blowers and a diffused air aeration system are provided in Digester/Storage Tank No. 5.
Piping interconnections allow several treatment schemes. Normally, waste activated sludge is first conveyed to
either Digester/Thickener No. 3 or No. 4, where most of the thickening takes place. Thickened solids are conveyed
to Digester/Storage Tanks No. 1 and 2, thickened on the centrifuges and stored in Digester/Storage Tank No. 5.
figim Thickened solids can also be conveyed directly to the centrifuges and then stored in Digester/Storage Tanks No. 1,
7

r'""
2, and 5. Digester/Storage Tank No. 1 also has facilities for adding lime to provide additional solids stabilization, if
needed.
Two centrifuges are provided for thickening or dewatering of digested solids. The centrifuges each have a hydraulic
capacity of 90 gpm and, with cationic polymer conditioning, produce a dewatered cake with a solids concentration of
approximately 15 percent. The dewatered cake is currently blended with digested solids from Digester/Storage
Tanks No. 1 and 2 and pumped at a solids concentration of approximately 4 percent to Digester/Storage Tank No. 5
for storage prior to land application. Centrate is returned by gravity to Influent Pump Station No. 1. Each centrifuge
is fed by a centrifuge feed pump. Polymer storage, mixing and aging is provided for either liquid or dry polymer.
The estimated maximum month solids production at 10.4 mgd is 16,843 Ibs/day based on influent wastewater
characteristics for the period August 2002 to July 2003. The Plant has already demonstrated the capability to
thicken, digest, and dispose (by contract land application) of the projected solids quantities at a permitted capacity of
10.4 mgd. Existing solids handling facilities are adequate for rerating to 10.4 mgd.
5.0 Conclusions and Recommendations
Wastewater flow at the Monroe WWTP is expected to exceed 90% of its permitted capacity in calendar year 2003.
Declining influent BOD concentrations over the past several years allow for increasing the permitted flow without
construction of new facilities. Actual plant performance in 2003 and an evaluation of process. and hydraulic capacity
confirms that the Monroe Plant can be rerated to 10.4 mgd capacity. Although not required for rerating to 10.4 mgd,
the City is proceeding with a $0.9 million project in 2004 that will expand the existing flow equalization basin and the
hydraulic capacity of the existing effluent filters. Proposed improvements will provide additional process safety factor
and improved treatment performance especially during extreme wet weather.
8

Table 1
Influent Pump Stations*
Pump Station No. 1
Number of pumps
Type
Capacity of each pump, mgd
Type of drive \' ?
Pump Station No. 2 ,�'�
1, (l
Number of pumps
�k v
Type
Design capacity of each pump, mgd
Type of drive
Total firm capacity (both stations), mgd
Influent Flow Measurement
Method of flow measurement
Number
Size, inches
Rotary Screens
Number
Screen openings, inches
4
Centrifugal, non -clog
3.5
Constant speed (3), variable speed (1)
2
Centrifugal, non -clog
6.5
Variable speed
20.5 2
Magnetic flow meter
4
1 @ 8 (Union County)
1 @ 14
1 @ 16
1 @ 18
2
0.06
' The influent pump stations pump the wastewater from the City of Monroe only. Flow from Union
County enters the plant directly upstream of the Screening Building.
9

Table 1 (Continued)
Design Data
Monroe WWTP
10.4 mgd Design Capacity
Flow Equalization Basin
Number of basins 1
Dimensions at water surface
Length, ft. 579
Width, ft. 194
Average depth, ft. 9
Side slope, horizontal to vertical 3:1
Volume, mil. Gal 6.3
Flow Equalization Pump Station
Number of pumps 2
Type Submersible
Capacity, each, mgd 3.5
Type of drive Constant speed
Aeration Basins
Number 5
Dimensions
Length, ft. 120
Width, ft. 4 @ 60
1 @ 90
Sidewater depth, ft. 16
Volume, each basin, mil. gal.
Total volume, mil. gal.
Detention time at design flow, hours
4 @ 0.86
1 @ 1.29
4.74
12.6
10

Table 1 (Continued)
Design Data
Monroe WWTP
10.4 mgd Design Capacity.
Aeration System
Type Fine bubble diffused air
Type of diffusers Membrane
Number of diffusers per basin 4 @ 1,060
1 @ 1,610
Total number of diffusers 5,850
Blowers
Number 3
a
Capacity of each blower, scfm 7,885
Firm capacity, scfm 15,770
Cv3 l
Secondary Clarifiers
Number 4
Diameter, ft. 85
Sidewater depth, ft. 12
Total volume, mil. gal. 2.04
Total surface area, ft.2 22,700 „
Overflow rate at design flow, gpd/ft.2 458
Return Activated Sludge Pumping Stations No. 1 and 2
Number of pumps, each station 3
Type Horizontal, centrifugal, non -clog, self priming
Capacity of each pump, gpm (mgd) 1,630 (2.35)
Total firm capacity, mgd 11.75
Type of drive Constant speed motor, adjustable sheaves
11

Table 1 (Continued)
Tertiary Filters
Number
Type
Dimensions of each filter
Length, ft.
Width, ft.
Depth of media
Anthracite, in.
Sand, in. 12
Gravel, in. 18
Total surface area, ft.2 2,880
Filtration rate at design flow, gpm/ft.2 2.51
Backwash Supply Pumps
Number 2
Capacity of each pump, mgd 14.1
Backwash Waste Pumps (to Flow Equalization Basin)
Number 2
Capacity of each pump, mgd 13.8
Chlorine Feed Facilities
Normal withdrawal of chlorine Gas
Number of chlorinators 2
Capacity, each, lb./day 500
Design Data
Monroe, WWTP
10.4 mgd Design Capacity_:
6
Dual media*, w/ air scour
24
20
24
Replacement with monomedia proposed in 2004.
12

(4"1°1
Table 1 (Continued)
Design Data
Monroe W1NTP
10.4 mgd Design Capacity
Sulfur Dioxide Feed Facilities
Normal withdrawal of sulfur dioxide
Number of sulfonators
Capacity, each, lb./day
Chlorine Contact Tanks
Number
Total volume, gal.
Detention time at design flow, rein.
Post Aeration
Gas
2
200
2
222,470
31 9�
Type Cascade
Aerobic Digesters/Thickeners/Storage Tanks
Number 5
Dimensions of each digester
Diameter, ft. 2 @ 65
1 @ 80
1@115
1 @140
Volume of each digester, mil. gal 2@0.25
1 @ 0.49
1@1.15
1 @ 3.00
Total volume, mil. gal 5.14
Aeration and mixing systems — Digesters No. 1 through 4
Type Mechanical, floating
Digester/Storage Tank No. 1
Aerators 2 @ 7.5 HP
Mixers 1 @ 40 HP, 2@ 7.5 HP
13

Table 1 (Continued)
Design Data
Monroe WWTP
10.4 mgd Design Capacity
Aerobic Digesters/Thickeners/Storage Tanks (Continued)
Digester/Storage Tank No. 2
Aerators
Mixer
Digester/Thickeners No. 3 and 4
Aerators 1 each @ 30 HP
Aeration and Mixing System — Digester/Storage Tank No. 5
Aeration System
Manufacturer Sanitaire
Type Fine bubble membrane
Number of diffusers 2,664
Blowers
Number 2
Type Positive displacement
Capacity, each, scfm 2,000
Horsepower 200
Centrifuge Dewatering Facilities
Number of centrifuges 2
Capacity, each, gpm (2% solids) 90
Sand Drying Beds (Backup)
Number 10
Dimensions of each bed
Length, ft. 120
Width, ft. 20
Total surface area, ft.2 24,000
3@ 40 HP
1@ 40 HP
14

City of Monroe
Wastewater Treatment Plant
Operational Stratagy
The City of Monroe wastewater treatment plant was originally constructed in
1965 as a 3.5 MGD extended aeration plant. It was expanded in 1976 and
upgraded to a 7.0 MGD conventional activated sludge plant which included a two
stage aeration process for BOQ and HN3 removal. In 1993 the facility was again
upgraded to a 9.0 MGD extended aeration process and this is the way it is
currently operated today. The plant superintendent has been at the facility since
1982 and has operated the facility under many conditions. In the 1980's flows to
the facility were pretty low but influent loading were extremely high with BOD's
being around 400 mg/I and NH3's pushing around 80 mg/I. The permit limits were
very leanient and chronic toxicity had not evolved. About 1989 during a permit
renewal period the facility found chronic toxicity in its permit for the first time and
since the facility discharges into a very small stream with a zero 7Q10 flow, the
instream concentration for the test was almost 100%. Initial testing was started
and it was quickly determined that something would have to be done as the
passing rate was averaging about 60%.
Plant flows during this period were averaging about 7.0 MGD and influent loading
rates were pretty high. Because of the high loading rates for BOD and NH3 the
mixed liquor suspended solids (MLSS) in the aeration basin were in tum high and
averaged about 5,000 mg/I. This posed a problem during chronic toxicity testing
periods due to solids lost from the secondary clarifiers which would carry over
into the chlorine contact chamber. These solids caused two problems in that they
would gather on the floor of the contact chamber causing denitrification to occur
and at times they would wash out of the chamber or wash through the chamber
and thus be captured by the effluent samplers leading to test failures. It was
decided that the main problem was due to the high influent loading rates to the
facility and that in order to lower the solids inventory of the facility to stop the
problem with solids washout that these loading rates would have to be lowered.
Lowering the loading rates to the facility fell on the shoulders of the pretreatment
unit. Again the average flow to the facility during this time was about 7.0 MGD
but what has not been mentioned until now was that 50% of this flow was from
industry and of that 3.5MGD about 3.0 MGD was from three large chicken
killing/processing operations. It was determined pretty quicky that these large
facilities were responsible for a huge amount of the influent loadings. All three
facilities were contacted, the problem was discussed, plans for these facilities
were created, time was given by the City, construction was completed and the
result was a large influent loading reduction to the wastewater treatment plant.

It needs to be understood that there were other industries also contributing to the
problem and not just these three but due to their size they were the major
contributors. In order to be fair to the industries the pretreatment unit had to be
more strict on its stance and thus all industries today have tighter permits than
before. Currently the City has about twenty permits issued to local industry and
most limit industry to typical Sewer Use Ordinance (SUO) values. If a industry
desires to discharge a wastestream over these values and the VWVfP can
handle the load it can be allowed but as a price the industry is surcharged for the
amount over SUO limits. This is done as a deterent for the high strength
discharges and to make it more fair for the citizens of Monroe who the facility
was constructed for.
Today the average flow for the WWTP is about 8.0 MGD but the average BOD is
275 mg/I and the average NH3 is under 20 mg/I. Due again to the potential of the
three large poultry plants they now have permanent refrigerated samplers at their
discharge points that have been installed by the pretreatment unit which sample
seven days a week. The pretreatment unit also visits each facility a minimum of
five times per week and many weeks make up to ten visits. This helps ensure
everyone is on the ball and helps ensure that loadings to the WWTP remain low.
In case anyone is wondering how the large poultry plants were able to lower the
strength of their discharges is was done by the installation of dissolved air
floation (DAF) units along with some other minor modifications.
As a final result of this now changed wastestream to the WWTP the amount of
solids inventory could be lowered. Instead of having a MLSS concentration of
5,000 mg/I the WVVTP is now operating with a MLSS concentration as low as
3,000 mg/I. This has kept our bugs growing happily and working hard. This has
lead to bigger/heavier floc which settles better and with lighter loadings of solids
to the secondary clarifiers we now have sludge blankets of less than one foot
each where in the past the sludge blankets could reach eight to ten feet. This
was a major reason for the solids washout in the past. This has also stopped
problems with denitrification that used to be common with the secondary
clarifiers. Today the VVWTP laboratory is used to control the WWTP solids
inventory. On a daily schedule they collect mixed liquor from the aeration basin
and conduct tests for MLSS, ph, SVI, settleability, microscopic examinations and
provide input to plant staff as to their findings. Through this method the facility is
able to control the influent loading and thus control the solids inventory of the
plant and elliminate all problems with solids washout and contaimination of the
effluent chronic toxicity sampling.

Wastewater Terms in Sludge Management
Activated Sludge
Sludge particles produced in raw or settled wastewater by the growth of organisms in
aeration tanks in the presence of dissolved oxygen. The term "activated" comes from the
fact that the particles are teeming with bacteria, fungi, and protozoa. Activated sludge is
different from primary sludge in that the sludge particles contain many living organisms,
which can feed on the incoming wastewater.
Activated Sludge Process
A biological wastewater treatment process which speeds up the decomposition of wastes
in the wastewater being treated. Activated sludge is added to wastewater and the mixture
(mixed liquor) is aerated and agitated. After some time in the aeration tank, the activated
sludge is allowed to settle out by sedimentation and is disposed of (wasted) or reused
(returned to the aeration tank) as needed.
Aeration Liquor
Mixed liquor. The contents of the aeration tank including living organisms and material
carried into the tank by either untreated wastewater or primary effluent.
Aeration Tank
The tank where raw or settled wastewater is mixed with return sludge and aerated.
Aerobes
Bacteria that must have molecular (dissolved) oxygen (DO) to survive.
Aerobic Digestion
The breakdown of wastes by microorganisms in the presence of dissolved oxygen. Waste
sludge is placed in a large aerated tank where aerobic microorganisms decompose the
organic mater in the sludge.
Bacterial Culture
In activated sludge, the bacterial culture refers to the group of bacteria classed as
AEROBES, and facultative organisms, which cover a wide range of organisms. Most
treatment facilities in the U.S. grow facultative organisms. Facultative organisms can
live when oxygen levels are low. And must have at least 0.5mg/L of dissolved oxygen to
function properly.
Biomass
A mass or clump of living organisms feeding on the wastes in wastewater, dead
organisms and other debris.
Ciliates
A mass of protozoans with short hairs on all parts of their bodies.
1

Denitrification
An anaerobic process that occurs when nitrite or nitrate ions are reduced to nitrogen gas
and bubbles are formed as a result of this process. The bubbles attach to the biological
flocs and float to the surface of the secondary clarifiers.
Diffused -Air Aeration
A diffused air activated sludge plant takes air, compresses it, and then discharges the air
below the water surface of the aerator through some type of air diffusion device.
Diffuser
A device that's porous used to break the air stream from the blower system into fine
bubbles in an aeration tank or reactor.
F/M Ratio
Food to microorganism ratio. A measure of food provided to bacteria in an aeration tank.
Facultative
Facultative bacteria can use either molecular (dissolved) oxygen obtained from food
materials such as sulfate or nitrate ions. Facultative bacteria can live under aerobic or
anaerobic conditions.
Filamentous Bacteria
Organisms that grow in a thread (weave or spider web type) or filamentous form. These
organisms are a common cause of sludge bulking or rising in the activated sludge
process.
MCRT
Mean Cell Residence Time, days. An expression of the average time that a
microorganism will spend in the activated sludge process.
MCRT, days = Solids in Activated sludge Process, lbs
Solids Removed from Process, lbs/day
MLSS
Mixed Liquor Suspended Solids, mg/L. Suspended solids in the mixed liquor of an
aeration tank.
Microorganisms
Very small organisms that can be seem through a microscope. Some microorganisms use
the waste in wastewater for food and inturn remove or alter much of the undesirable
matter.
Mixed Liquor
When the activated sludge in an aeration tank is mixed with primary effluent or the raw
wastewater and return sludge, this mixture is referred to as mixed liquor as long as it is in
the aeration tank. Mixed liquor also may refer to the contents of mixed aerobic or
anaerobic digesters.
2

Nitrification
An aerobic process in which bacteria change the ammonia and organic nitrogen in
wastewater into oxidized nitrogen (usually nitrate).
Protozoa
A group of microscopic animals (usually singled celled and aerobic) that sometimes
cluster into colonies and consume bacteria as an energy source.
RAS
Returned Activated Sludge, mg/L. Settled activated sludge that is collected in the
secondary clarifier and returned to the aeration basin to mix with incoming raw or
primary settled wastewater.
Rotifers
Microscopic animals characterized by short hairs on their front end.
Septic
This condition is produced by anaerobic bacteria. If severe, the wastewater turns black,
gives off foul odors, contains little or no dissolved oxygen and creates a heavy oxygen
demand.
Sludge Volume Index
This is a calculation used to indicate the settling ability of activated sludge (aeration
solids) in the secondary clarifier. The calculation is a measure of the volume of sludge
compared to its weight. Allow the sludge sample from the aeration tank to settle for 30
minutes. Then calculate the SVI by dividing the volume (ml) of wet settled sludge by the
weight (mg) of the sludge after it has been dried Sludge with an SVI of one hundred or
greater will not settle as readily as desirable because it is as light or lighter than water.
SVI = Wet Settled Sludge. ml X 1000
Dried Sludge Solids, mg
WAS
Waste Activated Sludge, mg/L. The excess growth of microorganisms which must be
removed from the process to keep the biological system in balance.
3

Trending Microscopic Examination of Wastewater
Observing the microorganisms in your plants mixed liquor on a regular basis year round
is the preliminary step in resolving future plant operational problems. When these
organisms are observed and the population of each one tracked and noted over a period of
time. You soon get the ability to trend upcoming conditions that your facility may be
headed into. Let's use the following as an example:
If the majority of the BOD is removed by microorganisms that are important indicators in
the activated sludge process like Protozoa and Rotifers.
The Protozoa eat the bacteria and help produce a clear effluent. Stalked ciliates.
The presence of Rotifers is a good indication of a stable effluent.
When these organisms are present in your plants mixed liquor suspended solids you can
expect a good settling activated sludge. And by using the proper RAS and WAS aeration
rates you can produce an effluent BOD of less than 10mg/L.
However if upon examining your plants activated sludge you only notice mostly
Filamentous Bacteria you've probably have waited to long. And need to employ a
vigorous procedure to get rid of the filamentous bacteria.
A constant dose of chlorine has helped our facility in the past. In fact, we not only got rid
of the filamentous bacteria but; we also managed to kill most of the algae blooms that
were such a problem in the past meeting our BOD limits.
Algae flakes would suck all of the oxygen out of our BOD samples and cause them to
drop out well before the five-day incubation period was up. We ran numerous tests on
both official and unofficial effluent BOD samples. One set was ran under normal
conditions, another set was ran using less effluent sample, while a third set was ran at full
strength but; placed in a separate incubator with a 40 watt appliance bulb that stayed on
for the 5 day test duration.
The results were eye opening enough that we immediately made changes to our facility
over the next couple of weeks and have steadily made upgrades each year.
Results on the full set of effluent BOD would have put us out of compliance. They all
dropped out with no final DO remaining.
Results on the lowered dilutions of effluent samples all read out. But as you all know the
lower the sample dilutions that you use the greater the multiplication factor will be in
calculating the final BOD result. And with a monthly average of 7.3 mg/L this was not a
long-term option.
The results from the full strength of effluent samples (which were not reportable or
used) yielded an oxygen uptake of < 2.0mg/L for the five-day incubation period. The
next week PVC loops were mounted on each clairifier so that a constant low dose of
chlorine could be applied 24/7 to both kill the algae as well as the filamentous bacteria.
4

Utilizing the microscope and multiple experiments we were able to begin learn about
seasonal changes in the bugs that live in our plant. Which bugs seamed to flourish more
in the summer months, compared to those that were more prevalent during the winter
months. We also noticed that we have several visiting species of bugs over the course of
the year. One particular species that shows up spring of each year only lived a short
period of time 2 to 3 weeks but caused serious odor problems long after it had died out
for the year.
The solution; when they show up use HTH directly on top of the clarifiers, and they die
out within 24 to 48 hours. After they have died out, their carcasses are wasted over into a
digester that was under constant aeration. Additional wasting is added daily to the
digester which eventually cover their carcasses and the smell is gone a week after they
show up, rather than early summer as before.
However let me say that chlorine is not the solution for each problem. Although it can be
used to help in many different cases, remember! Whatever amount of chlorine that
you add must be taken out before you discharge if you have a chlorine limit. The
WWTP in Monroe has a 17ug /L limits so we normally just feed more sulfur dioxide SO2
during periods like these.
Last fall for the 1 S` time we say a mutant variation of these same bugs. They were a lot
more resistant to chlorine. Minor construction was going on at the time on two clarifiers
this gave us a lot less time to process the wastewater after adding more chlorine. So
samples of the bugs were taken back to the lab and jar tests were performed on them at
various pH increases versus total kill time. We found out that at a pH increase to 10.2 the
total time kill was < 10 minutes, and the cost is considerably cheaper than chlorine and
the possibility of a chlorine violation drops 100%.
Using the microscope as a monitoring tool we were able to determine that chlorine could
be added at the rear of one basin that gave us even better control over the filamentous
bacteria. Which gave us a more consistent floc. The flow EQ equalization basin was
also retrofitted to help control algae blooms during the long hot summer days. The last
process control measure that's been added has been the pressure washing of the metering
vault at least once or twice per year. This controls the algae growth at the point of the
effluent samplers pick up point. This is where Environmental Testing Samples come
from so we really try to keep that as clean as possible.
5

274 Treatment Plants
tREATMENT MoCeGG
pEEr,2t4r4fWT
�NFLU,ENT
1
6CaEEN N&
GOT PMOvAt.0
vaE-aEaA-noN
FLOW METe2
09,/mAR9
7h'FQr4i�Nr
FUNCTION
tPEti10//ES,POoTS;.4e4GS, �S1L.1,GE
D1:605' 10AL4NOF/LL, O.P/F
ODSS/BLE G,Q/v.aiQET!/,�.f/Tvpl4.f/TFio
o?EMOvES 5A.VD /e4vz
(<1<!UL TO LANO F/LL)
F.QE$</ErVS w45TEly.4TE.2
�LIELPS' .Q��fiO!/ED/L
41EA6 fQES 4' eaeog Fzog'
6E01MENfA'fION ieEMOvES' 6E77ZEABL,E
AmOs Fi-orATION ficZ0.4740/FA•147:6:4241Z1
e.e;•AvoQQf)
recAxwAir
NAND �NG I T g4)OTy ,P p,20CESSES
,?EMOvFS S!/S17/(/OEO
Or55otvEo 51vzive
,eEMO!/ES S1l5PEAIDEO $OL/D$
OTf/E,2,ViLLlTQiylS
I DIhiNFEC?SON I ,e/LLS OATf/06EN/e BLlCTE,QzeI
EFFLUENT
Fig. 4.1 Flow diagram of a typical plant

Rerating Monroe to 10.4 mgd
zYJ3
Subject: Rerating Monroe to 10.4 mgd --`'—
Date: Wed, 22 Oct 2003 10:28:19 -0400
From: "j cramer" <j [e-mail]>
Organization: Hazen and Sawyer
To: <[e-mail]>, <[e-mail]>
CC: "Russ Colbath 1(E-maill)" <[e-mail]>,
"Kim Hinson" <[e-mail]>,
"James N. Struve" <[e-mail]>
Jackie,
Thank you for taking time to talk about the procedures for modifying
Monroe's NPDES permitfor an "interim" expanded flow of 10.4 mgd. Monroe's
current permit has three "pages" of limits at 9 mgd, 11 mgd, and 12.5 mgd.
An environmental assessment was done and FONSI issued and bids were received
in 2000 for the project to expand Monroe's WWTP to 12.5 mgd. The bids came
in high and the project was shelved. Since 2000, influent BOD's have
declined because of fewer industrial contributors and improved pretreatment
at the remaining industries. As most plants, the capacity of the Monroe
WWTP is based on organic loading. Since influent BOD concentrations have
gone down. the plant's flow capacity has increased. With increased rainfall
in 2003, flow in calendar year 2003 will exceed 90% of the current permitted
capacity of 9 mgd. Hazen and Sawyer has completed a process review. Actual
plant performance and process calculations confirm that the Monroe WWTP can
be rerated to 10.4 mgd. No new facilities are needed to rerate from 9 to
10.4 mgd; however, the City plans to spend almost $1 million to expand flow
equalization capacity and replace filter media as part of rerating.
Based on the above, what will the State require to modify Monroe's permit
for an expanded flow of 10.4 mgd? Based on our conversation, we are
anticipating submitting to DWQ a request for a permit modification(i.e.
application) with a 2 to 3 page attachment summarizing Hazen and Sawyer's
process evaluation. Plans and specifications for the expanded flow
equalization and new filter media will be submitted to Permits and
Engineering when completed. Please advise what procedures/submittals are
needed to modify Monroe's permit for a permitted flow of 10.4 mgd.
1 of 1 10/22/03 11:08 AM