NC0041696_Report_20020702

NPDES DOCUH NT !;CANNIN4 COVER SHEET
NPDES Permit:
NC0041696
Lake Rhodhiss WWTP
Document Type:
Permit Issuance
Wasteload Allocation
Authorization to Construct (AtC)
Permit Modification
Complete File - Historical
Engineering Alternatives (EAA)
Report
Instream Assessment (67b)
Speculative Limits
Environmental Assessment (EA)
Document Date:
July 2, 2002
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Wooten
Company
Engineering
Planning
Architecture
120 N. Boylan Avenue
Raleigh, NC
27603
919-828-0531
Fax: [phone]
Since 1936
June 28, 2002
Mr. David A. Goodrich, P.E.
Division of Water Quality
1617 Mail Service Center
Raleigh, North Carolina 27699-1617
RE: Total Phosphorus Optimization Study
Lake Rhodhiss WWTP
NPDES Permit No. NC00416i {
Town of Valdese, Burke County, North Carolina
Dear Mr. Goodrich:
JUL 2 2002
Pliny -s o .q OUlL1Ty
,(,E or?AMCH
The purpose of this letter is to provide you the results of the Total Phosphorus
Optimization Study conducted by the Town as per the requirements set for in the
NPDES Permit.
Based upon the monitoring data, the influent Total Phosphorus at the plant ranged
from 5.42 mg/L to 7.89 mg/L and averaged 6.875 mg/L. The major sources of
Total Phosphorus loadings at the plant include the wastewater discharges from the
Town of Valdese, Town of Drexel, a portion of Burke County, and industries in
the service area. Referring to the attached information on the sources of phosphorus
discharge to the Valdese Wastewater Treatment Plant, the Town of Valdese, Burke
County, Town of Drexel and industrial sources contribute 82.998, 7.876, 3.204
and 5.923 percentages of Total P discharge at the plant, respectively. Among the
industrial discharges, the Valdese manufacturing, Valdese Weavers (RC) and
Carolina Mills contributes approximately 37.25, 20.17, and 34.86 percent of Total
Industrial P loading at the plant, respectively.
The effluent Total P concentration at the Valdese WWTP ranged from 2.69 mg/L to
7.31 mg/L and averaged 4.97 mg/L. Average Total Phosphorus removal at the plant
was estimated to be approximately 28 percent.
In order to optimize the Total Phosphorus removal at the plant, the influent
characteristics in terms of COD/BOD5 ratio, BOD5/TP ratio and COD/TP ratios and
the wastewater treatment plant and sludge handling operations in terms of

operational changes were evaluated. Review of the monitoring data on influent
CODBOD5 indicated the ratios ranged from 1.56 to 4.76 and averaged 2.64. The
reported higher ratio of 4.76 seems to be significantly high and could be associated
with either discharge of textile wastes or unexpected industrial waste containing
high COD value or higher value of influent COD due to possible interference with
reduced inorganic species such as iron, manganous, manganese and sulfide that are
normally found in septic wastewater. Typical CODBODs ratios in municipal
wastewater are in the range of 1.5 to 2.0. The COD/BOD5 ratio is an important
factor in the evaluation of anaerobic selector zones for biological phosphorus
removal. Higher CODBOD5 ratios, for example greater than 2.0, indicate that the
wastewater may need more anaerobic hydraulic retention time for fermentation and
maintaining higher anaerobic biomass fraction to maximize biological phosphorus
removal. The influent COD/TP ratio at the plant ranged from 31.69 to 94.95 and
averaged 56.31. In order to achieve biological phosphorus removal in municipal
wastewater treatment plants, approximately 40 to 60 mg/L COD is required per each
mg/L phosphorus removed. It has been reported that in order to achieve an effluent
TP concentration of 1.0 mg/L or less, the influent COD/TP ratio should be greater
than 40. The reported influent COD/TP ratio at the plant is within the acceptable
range for biological phosphorus removal unless the COD attributed to the textile dye
waste may not be available for biological phosphorus removal. The influent
BOD5/TP ratio at the plant ranges from 13.11 to 30.07 and averages 23.87. The
BOD5/TP ratio is very important in evaluating biological phosphorus removal at the
plant. In order to achieve an effluent TP concentration of 1.0 mg/L or less, the
influent BOD5/TP ratio should be in the range of 20 to 35, depending upon the
operating SRT (Sludge Retention Time) of the system. The Valdese system is
operated at higher SRT to assimilate textile waste and will require BOD5/TP in the
range of 30 to 40 for biological phosphorus removal. The BOD5/TP ratio at the
plant is less than the required BOD5/TP ratio to achieve desired Total Phosphorus
removal at the plant. In order to optimize phosphorus removal at the plant, the
Town has recently modified the activated sludge system operation by shutting off
the first aerators in each aeration tank to create anaerobic/anoxic zones. The sludge
recirculation rate is also increased to achieve simultaneous denitrification in the

anaerobic/anoxic zone of the aeration tanks. The results of the biological
phosphorus removal evaluation will follow later.
Monitoring of the sludge handling facilities, more particularly the recycle flows
from the sludge thickening tanks and centrifuge sludge dewatering operations,
indicate high concentrations of Total Phosphorus in decant or supernatant from the
sludge thickening tanks and centrate from the centrifuges. The average Total
Phosphorus concentrations in the sludge thickening tank's decant recycle and
centrifuge centrate recycle are 9.93 mg/L and 16 mg/L, respectively. In order to
avoid septic conditions and release of phosphorus in decant recycle flow, the Town
has recently installed the diffused aeration system in the sludge thickening tanks.
The aeration system is operated in the cyclic mode and the cyclic aeration operation
will help control release of phosphorus and Total Nitrogen in the decant and
centrate recycle flows. The Town will furnish the results of the change in sludge
handling operations on the decant's and centrate's Total Phosphorus concentrations
at a later date.
The Town is committed to reduce the Total Phosphorus discharge and we are
optimistic that the recent modifications and operational changes will help reduce the
Total Phosphorus discharge from the plant.
Should you have any questions concerning this matter, please call me at (919) 828-
0531 or Mr. Alan Abee at [phone].
Sincerely,
THE WOOTEN COMPANY
V(1%UN s1
a. a-'11._
Shankar R. Mistry, Ph.D., P.E.
SRM:hmm
Attachment
c: Mr. Alan Abee, Superintendent, Valdese WWTP

0
SOURCES OF PHOSPHORUS DISCHARGE TO VALDESE WWTP
1 Industrial Sourses
Name of Industry Ave, Daily Flow Total P Total P % of Total P
mgd m g/ L lb/day Discharge
Alba (John Louis Plant)
Burke Mills
Houston Hosiery
Valdese Textiles
Valdese Manufacturing
Valdese Weavers (RC)
Valdese Weavers (LL)
Carolina Mills
Robinson Hosiery
Waldensian Bakeries
Total
Average
2 Burke County
3 Town of Drexel
4 Town of Valdese
0.093
0.746
0.050
0.090
0.611
0.455
0.221
1.187
0.008
0.042
2.664
0.350
0.432
0.143
3.749
1.430
0.67
9.724
0.543
13.900
9.972
0.724
6.569
1.660
7.856
56.551
5.305
1.109
4.168
4.055
0.408
70.831
37.841
1.334
65.030
0.111
2.752
187.639
15.498
5.715 20.590
7.023 8.376
216.991
6.940
5 Percentage of Total Phosphorus Contribution by Source
Source Identity
Town of Valdese
Burke County
Town of Drexel
Industrial
Total
Ave, Daily Flow
mgd
3.749
0.432
0.143
0.350
4.674
Total P
mg/L
6.940
5.715
7.023
5.305
Total P
lb/day
216.991
20.590
8.376
15.485
261.442
Ave. Influent Total P conc. at Valdese WWTP= 6.707
6 Effluent Total
Month, Year
Jan. 2001
May. 2001
Jun. 2001
Jul. 2001
Aug. 2001
Sep. 2001
Oct. 2001
Nov. 2001
Dec. 2001
Jan. 2002
Feb. 2002
Mar. 2002
Apr. 2002
Average
P Cocentration at Valdese WWTP
Total P.,mg/L
2.69
6.31
4.70
4.82
3.63
4.67
4.68
6.70
4.53
4.67
2.91
7.00
7.31
4.97
0.59
2.22
2.16
0.22
37.75
20.17
0.71
34.66
0.06
1.47
100.00
% of Total P
Discharge
82.998
7.876
3.204
5.923
1 00.000