Comparison of Three Wet Weather Flow Treatment ... - IngentaConnect

WEFTEC 2012

Comparison of Three Wet Weather Flow Treatment Alternatives to Increase Plant Capacity Don Esping1*, Bill Krill1, Denny Parker1, Jose Jimenez1, Jim Fitzpatrick2, Fenghua Yang3, Tim Bate3 1 Brown and Caldwell 2 Black & Veatch 3 Milwaukee Metropolitan Sewerage District *Email: [email protected] ABSTRACT The Milwaukee Metropolitan Sewerage District is evaluating alternatives to increase the South Shore Water Reclamation Facility wet weather treatment capacity from 300 to 450 million gallons per day. In this study, side5by5side testing of biological contact treatment, chemically enhanced sedimentation, and compressible media filtration was conducted to define treatment performance and design criteria for treating wet weather flows. Based upon wet weather testing conducted to date on primary influent, biological contact achieved the lowest effluent concentrations and met all project effluent water quality goals when operated at mixed liquor concentrations between 1600 and 2000 mg/L and contact times of 15 minutes. Compressible media filtration effluent solids and biochemical oxygen demand concentrations were also less than the project effluent goals when operating at filtration rates of 7.5 gpm/sf. Chemically enhanced sedimentation testing was inconclusive due to equipment malfunctions during testing. At the time of this writing, additional wet5weather testing was ongoing. KEYWORDS Auxiliary Treatment, Wet Weather Treatment, Biological Contact Treatment, Chemically Enhanced Sedimentation, Compressible Media Filtration INTRODUCTION The Milwaukee Metropolitan Sewerage District (MMSD) is evaluating alternatives to increase the South Shore Water Reclamation Facility (SSWRF) wet weather treatment capacity from 300 to 450 million gallons per day (mgd). To achieve this capacity during wet weather storm events, the MMSD 2020 Facilities Plan recommended routing 300 mgd of screened and degritted plant influent (primary influent) flow directly to secondary treatment and treating the remaining 150 mgd of flow using an auxiliary wet weather treatment process. This study evaluated three auxiliary wet weather treatment technologies to treat primary influent or primary effluent during wet weather flow events as summarized below. •

Chemically Enhanced Sedimentation (CES) – This process involves the addition of chemical coagulants such as ferric chloride and flocculants to primary influent to improve fine particulate and colloidal solids treatment performance during sedimentation. CES is sometimes referred to as chemically enhanced primary treatment (CEPT) when used for the treatment of dry weather flows ahead of a biological process.

Copyright ©2012 Water Environment Federation. All Rights Reserved. 2282

WEFTEC 2012

(BOD5/TSS/NH35N/TP) milligrams per liter (mg/L). Fecal coliform testing is the focus of another study and not presented here. Table 1. South Shore WRF Effluent Water Quality Requirements Demonstration NPDES Operations Study Goals Contract Units Permit

Item Total BOD5 mg/L 30a /45b 15a Total Suspended Solids mg/L 30a /45b 15a a Total Phosphorus mg P/L 1.0 1.0a Ammonia5Nitrogen mg N/L Seasonal 5a Fecal Coliformc (no./100 mL) 200 100 a. Monthly average b. Weekly average c. Geometric mean

35 35 1 5 55

APPROACH

The first step in the project was to conduct bench5scale jar testing to simulate CES and BC treatment processes. CES jar tests were used to screen different coagulants and flocculants for their ability to improve TSS removal. BC treatment jar tests were conducted to define the SSWRF mixed liquor bioflocculation kinetics and flocculation potential to establish target operating mixed liquor suspended solids (MLSS) concentrations and contact time for the demonstration facilities. The bench scale test results were used to develop work plans for the design and construction of demonstration facilities to demonstrate the auxiliary wet weather treatment concepts at the SSWRF. Wet weather testing was completed after construction of the demonstration facilities. BENCH SCALE TESTING Chemically Enhanced Sedimentation (CES). Unlike CES facilities designed for wet weather flow treatment with surface overflow rates (SOR) of up to 6,000 gallons per square foot5day (gpd/sf), the SSWRF CES high5rate treatment concept is to treat a maximum SOR of 1500 gpd/sf (150 mgd) with the remaining 300 mgd being routed directly to the existing secondary treatment facility. This flow scheme maximizes uses of the existing treatment facilities, maximizes CES treatment performance, and also minimizes CES chemical usage. Figures 2 and 3 show the bench5scale CES jar testing results for the most favorable coagulants and flocculants including the dosage combinations. Supernatant TSS and COD concentrations from the optimum ferric chloride and polyaluminum chloride (PAX) dosing with anionic polymer were essentially the same. Given the lower cost of ferric chloride, 40 mg/L of ferric chloride with 0.5 mg/L Clarifloc A5210P (anionic polymer) were selected as the target chemical dosages for demonstration testing.


WEFTEC 2012

Table 2. Summary of Biological Flocculation Kinetic Coefficients Parameter

Residual Concentration, mg/L First*Order k, L/min mg

Total Suspended Solids Particulate COD Colloidal COD

11.3 6.5 18.5

3.42 x 1054 1.75 x 1054 5.32 x 1055

Figures 5 through 7 show the effect of mixed liquor concentration and contact time on the removal of TSS, particulate COD, and colloidal COD in a plug flow reactor using the bioflocculation kinetic coefficients in Table 2. As seen in these figures, the MLSS concentration and the residence time in the biological contact treatment tanks will play a major role in the removal of particulate substrate by biological flocculation during high5flow, wet5weather conditions. Based on the kinetic parameters determined at the SSWRF, it can be seen that complete removal to residual TSS concentrations can be achieved with MLSS concentrations and contact times ranging from 1,000 to 2,000 mg/L at 20 to 12 minutes, respectively. The removal rate of colloidal COD is slower than TSS. Complete removal to residual colloidal COD requires operating MLSS concentrations and contact times in excess of 2,000 mg/L and 30 minutes, respectively. These results are consistent with observations by Jimenez et al. (2004 and 2005 and 2005b) where the removal of colloidal COD was found to be slower than larger particles since it is believed the colloidal material includes exocellular polymer substances produced by the biomass; hence, it might be charged differently than wastewater particulate substrate. Finally, the particulate COD removal rate is slightly slower than for TSS; and complete removal to residual particulate COD can be achieved with mixed liquor concentrations and contact times ranging from 1,000 to 2,000 mg/L at 30 to 15 minutes, respectively. Based upon bench scale testing, an initial target MLSS range of 1500 to 2000 mg/L with a corresponding contact time of 15 to 20 minutes was selected for demonstration testing.


WEFTEC 2012

Biological Contact (BC) Treatment. Table 3 presents a summary of BC pilot scale demonstration testing completed on simulated primary influent wet weather flows. Each test run was four hours in duration. BC effluent suspended solids (ESS) ranged from 6 mg/L at the most favorable bioflocculation conditions tested (MLSS=2070 mg/L and 20 minutes HRT) to 34 mg/L at the least favorable bioflocculation conditions (MLSS of 1650 mg/L and 15 minute HRT). Simulated effluent water quality met the SSWRF target criteria of 35 mg/L ESS and 1 mg/L total phosphorus. Table 3. Item Influent stream MLSS Influent COD TSS BOD5 TP Reactor 3 Contract time Effluent TSS Reactor 4 Contact time

Biological Contact Treatment Simulated Wet Weather Test Results.* Units

10/12/2011

10/17/2011

10/17/2011

Blend of primary influent and secondary effluent

mg/L

1653

1882

2069

mg/L mg/L mg/L mg/L

190 95 68 1.8

160 79 64 1.8

130 66 51 1.3

minutes mg/L

15 34

22 15

15 7

minutes

20

29

20

Effluent COD

mg/L

110

51

59

Effluent TSS Effluent TP

mg/L mg/L

25 1.0

19 0.53

6 0.36

*Demonstration Facilities do not include secondary clarifiers. Effluent represents reactor supernatant concentrations after 20 minutes flocculation and 30 minutes settling in 2L beaker.

Compressible Media Filtration (CMF). CMF pilot scale demonstration testing was also completed during the Fall of 2011 using simulated primary effluent wet weather flows. In addition, CMF test runs with ferric chloride and return activated sludge (RAS) addition were conducted to determine if CMF performance could improve with addition of these coagulants/bioflocculants. All test run durations were 20 hours, except October 27 and 28 test runs which lasted 3 hours. The CMF filter was primarily operated on test run days only and not continuously operated (24/7) during the simulated wet weather testing period. Table 4 summarizes the CMF simulated wet weather test results. CMF ESS water quality was less than 13 mg/L for all cases; however target effluent BOD5 of 35 mg/L was not consistently achieved, especially at filtration rates of 7.5 gpm/sf. Effluent TP water quality goals of 1.0 mg/L were met when the CMF influent was dosed with 30+ mg/L ferric chloride. RAS addition to the CMF influent was tested to evaluate the potential for enhancing soluble substrate removal. Demonstration testing showed roughly 5 percent soluble COD removal in the RAS filter runs; which was similar to non5RAS runs. It should be noted that since the BC and CMF units were Copyright ©2012 Water Environment Federation. All Rights Reserved. 2292

WEFTEC 2012

Table 4. Item Influent stream

Units

Filtration rate

gpm/sf

Additive

Compressible Media Filtration Simulated Wet Weather Flow Test Results.

10/12/2011 10/13/2011 10/18/2011 10/19/2011 10/20/2011 10/21/2011

10/27/2011

10/28/2011 10/31/2011 11/1/2011

Blend of primary efffluent and secondary effluent

5.5

7.5

5.5

7.5

5.5 7.5 80 mg/L 135 mg/L 33 mg/L RAS RAS FeCl 3

5.0 63 mg/L FeCl3

93 mg/L FeCl3

7.5 24 mg/L FeCl3

5 31 mg/L FeCl3

7.5 40 mg/L FeCl3

55

55

55

55

55

mg/L mg/L mg/L

230 190 60

200 160 34

82 51 19

100 79 22

160 71 58

250 86 100

150 77 31

110 65 15

150 77 31

160 95 27

BOD5 TP

mg/L mg/L

97 3.2

67 2.2

25 0.99

36 1.9

87 2.7

140 4.4

49 55

40 55

40 1.4

40 1.8

Effluent COD

mg/L

180

190

74

82

97

110

90

83

66

66

76

95

Soluble COD TSS

mg/L mg/L

130 13

150 11

50 8.4

59 5

68 7

82 10

53 23

70 12

55 10

55 12

71 5

30 8

BOD5 TP

mg/L mg/L

43 2.2

57 2.0

19 0.9

37 1.7

28 1.6

47 2.3

30 55

27 55

18 55

25 55

24 0.20

42 0.3

Influent COD Soluble COD TSS


WEFTEC 2012

tested on different influent streams (primary influent for BC and primary effluent for CMF) and had different test durations, a direct comparison of their treatment performance should not be made.

WET WEATHER TESTING Wet weather demonstration testing was conducted on May 7, 2012. During this test, each treatment alternative test train was operational and fed primary influent. Testing commenced at approximately 7 am. Figure 11 shows the test start time was roughly 8 hours into the wet weather flow event. The BC pilot and CES primary clarifiers were operated for approximately six hours per the test protocol. It should be noted the CES submersible mixer used for chemical mixing in the channel was malfunctioning during this test. The CMF operation began on about April 26th processing dry weather primary influent flows in an effort to grow a biologically active layer on the filter media for enhanced soluble BOD5 removal. The CMF wet weather effluent sampling started 9 am and operated at a feed rate of 7.5 gpm/sf. The CMF test run lasted 11 hours as the system is equipped with an automated influent sampler, effluent sampler, and backwash system. Figures 12 through 18 show the May 7, 2012 demonstration test results. The BC pilot unit produced the best effluent quality and met all the target effluent criteria with TSS, BOD5, NH35 N and TP discharges levels less than 10/10/4/ 0.5 mg/L respectively. BC was the only alternative which demonstrated consistent soluble substrate removal of ammonia, soluble phosphorus and soluble COD (38, 36 and 17 percent respectively). Increasing the BC reactor contact time from 16 to 22 minutes had negligible impact of effluent quality. The MLSS concentrations varied from 1400 to 2000 mg/L during the test as shown in Figure 19. All CMF effluent sample concentrations were less than the target BOD5 and TSS effluent quality criteria during the test, even for the extended period when the other trains were not operating. CMF effluent ammonia and TP concentrations were roughly 1.5 to 2.0 mg NH35N/L and 0.2 mg P/L higher than the BC effluent during similar periods of operations. The CMF effluent did increase above the target ammonia and TP effluent values during the latter part of the test; however, the average effluent TP concentration was less than the target value of 1.0 mg P/L. Comparative conclusions of test data after 1300 hours can not be drawn since the other test trains were not operating during this period. CES surface overflow rates (SORs) during the test average approximately 2700 gpd/sf. This SOR is higher than the CES design SOR of 1460 gpd/sf to treat 150 mgd of wet weather flow in the existing primary clarifiers. Lag time in chemically treated influent passing through the primary clarifier was roughly 0.7 hours at 2700 gpd/sf. However even at 2700 gpd/sf, it is anticipated that CES treatment performance would be much improved. It is speculated the effluent quality was negatively impacted by critical mechanical equipment (chemical submersible mixer) malfunctioning and higher SORs. Lack of soluble phosphorus removal as shown in Figure 16 along with low TSS and COD removal compared to jar testing suggests the ferric chloride dose of 40 mg/L and anionic polymer of 0.5 mg/L was not effectively mixed into the flow.


WEFTEC 2012

Jimenez, J., Parker, D., Bratby, J., Schuler, P., Campanella, K., and Freedman, S. (2005a) “Biological Wet Weather Treatment: Biological Contact Process Provides Secondary Treatment for Wet Weather Flows.” Water Environment & Technology 17 (12), 53557. Jimenez, J. A., La Motta, E. J., and Parker, D. S. (2005b) “Kinetics of Removal of Particulate Chemical Oxygen Demand in the Activated Sludge Process.” Water Environment Research 77 (6), 4375 446. Milwaukee Metropolitan Sewerage District. (2007) 2020 Facilities Plan. June.
