NC0023736_Nutrient Optimization Study_20070320

NPDES DOCUMENT SCANNING COVER SHEET
NPDES Permit:
NC0023736
Gunpowder Creek WWTP
Document Type:
Permit Issuance
Wasteload Allocation
Authorization to Construct (AtC)
Permit Modification
Complete File - Historical
Engineering Alternatives (EAA)
Correspondence
Owner Name Change
fepor-/—
Instream Assessment (67b)
Speculative Limits
Environmental Assessment (EA)
Document Date:
March 20, 2007
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City of Lenoir
Public Utilities Department
Gunpowder Creek WWTP
P.O. Box 958
Lenoir, North Carolina 28645
March 20, 2007
ATTN: Central Office
NC DENR / Division of Water Quality
1617 Mail Service Center
Raleigh, NC 27699-1617
Subject: Nutrient Optimization Study for the City of Lenoir
Gunpowder Creek WWTP (Permit # NC0023736)
Central Office:
The City of Lenoir's Gunpowder Creek WWTP (Permit # NC0023736)
is required to perform a Nutrient Optimization Study, originally due on
January 1, 2007.
apologize for the tardiness of the study. Please accept this
submission as compliance for the requirement.
If you require any other information, please call me at 828-757-2198.
Thank you for your assistance.
Sincerely,
Monte L. Wa
Superintendent Wastewater Treatment
City of Lenoir

GUNPOWDER CREEK WASTEWATER TREATMENT
PLANT
NUTRIENT OPTIMIZATION STUDY
The Gunpowder Creek Wastewater Treatment Plant operates on
Sequencing Batch Reactor (SBR) technology. Specifically, the
process utilizes the system design from Aqua -Aerobic Systems, Inc,
Rockford-, Illinois.
The system uses up to four (4) individual circular SBR tanks, with all
biological and separation processes taking place in each tank. The
phases are timed and include 1) Mix Fill Phase 2) React Fill Phase 3)
React Phase 4) Settle Phase 5) Decant — Idle — Waste Sludge
Phase.
During the Mix Fill Phase, the tank mixer is on and the aeration
system (diffused air) is off. Raw wastewater is pumped into the
reactor (tank) and is dispersed into the existing mixed liquor. Any
residual dissolved oxygen (D.O.) is quickly used, and the only
existing oxygen in the tank is in the molecular form, primarily nitrates
(anoxic state). Nitrates are reduced to nitrogen gas during this
phase. After the nitrate concentration diminishes, the lack of
molecular D.O. encourages anaerobic conditions. With the help of
the inflow of BOD into the reactor, phosphorous. is converted to
orthophosphate. The orthophosphate is later used in the creation of
new bacterial cell mass.
The diffused air system is on, along with the mixers, during the React
Fill Phase. Influent flow continues into the reactor. The tank
becomes aerobic, oxidizing BOD and TKN. Nitrifiers convert the
ammonia, from incoming wastewater or from the breakdown of TKN,
into nitrites and nitrates.
The React Phase includes mixing and diffused air only. The influent
flow is discontinued. This phase acts as a "polishing step" to further
decrease BOD, TKN and ammonia.
NPpE5 * NC 602.3736

Gunpowder Creek WWT
NH3
(Mo.
Avg.)
TKN
TOT N
6/22/06
1.47
4.72
4.08
7/10/06
0.07
7/11/06
1.75
6.27
8/24/06
0.47
8.56
10.58
9/21/06
3.52
13.00
15.77
10/23/06
0.07
2.10
7.08
11/29/06
0.50
1.29
3.66
12/6/06
1.74
0.77 .
3.39
1.38
3.49
6.50
average
%
removal
92.84%
88.41%
77.78%
P Effluen
TOT P
3.25
t
NO2 +
NO3
NH3
Gunpowder Influent
TKN
TOT
N
TOT
P
1.47
21.30
36.10
36.20
4.95
5.20
0.23
4.28
2.20
2.56
3.11
4.52
2.02
2.77
4.98
20.40
34.60
34.80
5.00
2.37
2.62
3.17
3.20
19.30
30.10
29.27
5.50
42.29%
The treatment objectives according to the design parameters are as
follows: Effluent ammonia, 1 mg/L; effluent TKN, 5 mg/L. The
ammonia goal was met on seven (7) of the twelve (12) months during
the year; the TKN goal was met ten (10) of the thirteen (13) sampling
events. The occasions that these goals were not met were due to
mechanical issues (tank level sensor malfunction and blower
problems). Overall removal percentages were good. Nitrate + Nitrite
levels are estimated to be approximately 10 - 25% of the levels
expected for a plant utilizing conventional aeration without biological
nutrient removal.
There are three(3)Significant Industrial Users (SIUs) that contribute
9
flow to the Gunpowder Creek WWTP: Lenoir Mirror Plant #1 (permit
# 007); Cajah Mountain Hosiery (permit # 0008); and American &
Efrid Plant #02 (permit # 0011). Of the three, only Cajah Mountain
Hosiery contributes significantly to the influent nutrient loading. There
is a permit limit of 40 mg/L for ammonia as N. TKN and total
phosphorous contributions are not at the significant level for the
industry, but do exceed the influent values slightly (last three years
data averages: TKN, 33.3 mg/L; and total P, 9.62 mg/L). The
industry dyes and finishes hosiery. Their production has been down
over the past two years, as has their nutrient contribution.
This concludes the Nutrient Optimization Study for the Gunpowder
Creek VVWTP.

The Settle Phase allows the tank to act as a clarifier. No flow is
entering the reactor (except under extreme flow conditions). Also the
mechanical mixer and diffused air are off, providing a quiescent
environment for solids -liquid separation.
After the reactor settles for a set period of time, the floating
decanter's weir opens, allowing the supernatant to discharge into the
effluent equalization basin. The weir closes when the tank achieves
a predetermined level (11.1'). When the decant is completed, the
reactor goes into "idle", which allows the system to compensate for
any changes in flow. The waste sludge phase ends the process.
All SBR tanks are monitored (twice weekly) for the following: MLSS,
MLVSS and settleable solids during the react phase; D.O.; SBR
effluent TSS and ammonia.
The primary ways to control the biological processes within the SBRs
are through altering wasting times and changing phase times,
especially due to seasonal / temperature changes. If the parameter,
ammonia, begins to rise in the SBR effluent, then either the wasting
time is reduced (to increase sludge age) or the air supply is
increased. During colder weather months, the MLSS is kept at a
higher level than normal to compensate for reduced bacterial activity.
Generally the air supply is fixed, with two blowers running. But
sometimes there is a mechanical problem which manifests itself by
one of the following: 1) lack of observed turbulence in the react fill or
react cycles, or 2) a low basin D.O. in these cycles. The problem
(such as a broken belt, bad electrical relay, etc.) is found and
repaired as soon as possible.
Phase times, like wasting times can be changed from the main SBR
control panel. During warmer weather, it is desirable to have
increased amounts of air supplied to the SBR tanks. When
temperatures are cooler, less blower supplied air is necessary. Air
supply is critical to these phases, as too little D.O. can lead to
decreased BOD and ammonia removal efficiencies; and worst case,
bacterial kill, leading to septic conditions. Too high D.O. can cause
undesirable foaming problems; can waste energy; can make settling

difficult; and can interfere with the nutrient removal process. Both
phosphorous and nitrogen (as nitrate) removal depend on anaerobic /
anoxic conditions at the right phase. If there is D.O. carryover from
the react phase, then phosphorus and nitrogen removal efficiencies
will be decreased.
Listed in the table below are phase time examples, based on
seasonal changes:
Phase
Times
Times
Mix / Fill
60
46
React / Fill
110
124
React
40
46
Settle
60
75
Decant / Waste / Idle
70
49
Total Time
340
340
Total Cycles / Day
4.24
4.24
Date Changed
12/1/2005
5/24/2006
Note that the colder months, air is "limited to 150 minutes (sum of
React / Fill and React cycles). During the warmer months, air is
supplied for a total of 170 minutes.
Below are the nutrient data for the Gunpowder Creek WWTP for the
calendar year 2006:
Gunpowder Creek VW TP Effluent
Gunpowder
Influent
NH3
(Mo.
Avg.)
TKN
TOT N
TOT P
NO2 +
NO3
NH3
TKN
TOT
N
TOT
P
1/9/06
0.43
20.80
16.50
16.80
7.60
1/10/06
0.90
3.81
3.80
2.91
2/23/06
0.52
1.99
5.27
3.22
3.28
3/9/06
4.10
1.74
4.34
2.63
2.60
4/25/06
3.80
5.70
4.05
14.70
33.20
4.45
5/9/06
0.87
1.67
3.52
2.73
1.85
5/31/06
4.41
9.61
5.20