Matthew Cotton Process Group Manager. PNCWA October 27, 2010

Transcription

1 Quantification of SBOD 5 and PBOD 5 Removal via Coupled Biological Contact Reactor and Ballasted High-Rate Clarification System for Wet Weather Treatment Applications Matthew Cotton Process Group Manager PNCWA October 27, 2010

2 Key Terms / Phrases Activated Sludge / Biomass / MLSS Sorption High-Rate Clarification (HRC) Biological Contact Tank (BCT) Ballasted Flocculation True Soluble CBOD & BOD (TSCBOD, TSBOD) Sludge Retention Time (SRT) Secondary Treatment Floc/Filter Method (Mamais, et. al., 1993)

3 Presentation Outline 1. History / Background Wet Weather Flows 2. Typical Biological Treatment Designs Process and Flow Schematics HRC, Biological Contact Tank coupled with HRC 3. Purpose of Testing 4. Bench-Scale Testing Set-Up / Procedure 5. Summary of Results / Data 6. Conclusions 7. Determination of Adsorption Rate Constants 8. Summary of Modeling Results 9. BCT-HRC pilot study in Knoxville, TN. 10. Acknowledgements 11. Questions?

4 Background / History Successful arguments have been made that: Typical physical-chemical processes do not provide biological treatment. While physical-chemical processes (i.e. HRC) may meet secondary treatment requirements w.r.t. TSS and BOD 5, higher concentrations of pathogens still remain. A possible solution is to provide an aerated solids contact tank upstream of the HRC, meeting the requirement for biological treatment. Note that blending of effluents with a physical-chemical process is not specifically prohibited during wet weather flows. Permitting can be location-specific as some plants are allowed to blend effluents.

5 Tertiary and Wet Weather Treatment Normal Operation Storm Operation WWTP WWTP Excess Q Tertiary Mode HRC HRC Wet Weather Mode- No biological treatment Receiving Water Receiving Water

6 Application Schematic Wet Weather INFLUENT WASTEWATER PEAK WET WEATHER WASTEWATER FLOWS FINE BAR SCREENS ENHANCED HIGH RATE CLARIFICATION (PHYSICAL/CHEMICAL) Uncontrolled Discharge Flow Equalization / Storage Biological Treatment Activated Sludge Fixed Film To Sludge Processing DISINFECTION PRIMARY CLARIFIER (PHYSICAL) To Sludge Processing SECONDARY (BIOLOGICAL) FINAL CLARIFIER (PHYSICAL) REAERATION EFFLUENT Schematic Courtesy CDM

7 BCT-HRC Process Schematic

8 Plant Schematic Biological Contact Tank with HRC Flow to Activated Sludge Plant Influent Headworks Screening Grit Primary Clarifier Aeration Basins Secondary Clarifier Disinfection Effluent To Outfall Sludge RAS Flow to Solids Contact Ballasted Clarification I Biological Solids Contact Tank C Maturation Settling Coagulant Polymer

9 Bench-Scale Testing Purpose Quantify Soluble and Particulate CBOD removal capabilities of the BCT-HRC process. Determine BCT contact time required to achieve secondary treatment goals. Model True Soluble CBOD sorption rate constants for WWTPs with different SRTs.

10 Bench-scale Testing Procedure (Outline) Sample ~30 L of Raw Wastewater. Sample ~15 L of RAS and allow to settle/thicken. Add Raw Water to Bio-contact tank. Start aeration and timer. Add RAS to contact tank to achieve set MLSS. Immediately sample, filter and floc filter for SCBOD, TSCBOD and TSS analyses (t=1 minute). At time t = 5, 10, 15 minutes, etc sample and filter (SCBOD) or floc filter (TSCBOD). Conduct Ballasted jar testing on aerated samples (e.g. 10 and 25 samples) and analyze for Total CBOD, SCBOD and TSCBOD. Ballasted Floc Jar Test Procedure: Add metal salt coagulant & ballast (sand) to raw sample Mix at 300 rpm, 2 min Add polymer Mix at 200 rpm, 45 sec Settle for 2 min Filter a portion of the jar test effluent for SCBOD analyses. Flocculate and filter (0.45 um) a portion of the jar test effluent for TSCBOD analysis. Floc/Filtering for TSCBOD: ZnSO4 addition Caustic addition (to 10.5 ph) Settle/Filter = Colloid-free

11 Bench-Scale Testing Set-up

12 Bench-Scale Aeration Tank

13 Bench Scale Testing Testing conducted at two wastewater treatment plants WWTP A Long SRT (12 days) WWTP B Short SRT (3 days)

14 WWTP A SCBOD Sorption Rates per Gram Biomass per Minute Time Soluble (mg/min/g) True Soluble (mg/min/g) SCBOD Sorption Rate per Gram Biomass per Minute Soluble CBOD True Soluble CBOD 35.0 Soluble CBOD Sorption (mg/min/g) Day Time (minutes)

15 WWTP A (Raw SCBOD / TSCBOD = 59 / 23 mg/l, 44 / 18 mg/l on Day 2) Soluble CBOD vs. Time (CT MLSS = 880/780 mg/l) Soluble CBOD True Soluble Colloidal % Day 1 Day % Soluble CBOD (mg/l) % 64.4% 67.8% 59.1% 57.8% 51.7% 60.0% 54.4% 58.3% 71.7% time (minutes)

16 WWTP B SCBOD Sorption Rate per Gram Biomass per Minute Time Soluble (mg/min/g) True Soluble (mg/min/g) WWTP B - Soluble CBOD Sorption Rate per Gram Biomass per minute True Soluble Soluble CBOD Sorbed Soluble CBOD(mg/min/gramML) Time (minutes)

17 WWTP B (Raw SCBOD = 100 mg/l) Time Soluble CBOD (mg/l) True Soluble CBOD (mg/l) WWTP B - Soluble CBOD vs. Time (Contact Tank MLSS = 1100 mg/l) Soluble True Soluble Colloidal 25 Soluble CBOD (mg/l) % 79.0% 90.0% 88.0% 87.0% 93.8% 88.0% 93.0% 90.2% 92.4% 83.0% 91.3% time (minutes)

18 WWTP B - Soluble CBOD Removal SCBOD Raw 100 % Removal 1 min min min min min min Rocky Mount, NC - Soluble CBOD Removal vs. Aeration Time Raw Soluble CBOD (mg/l) min 5 min 10 min 15 min 20 min 25 min 0 Time (minutes)

19 WWTP B - True Soluble CBOD Removal TSCBOD Raw 52 % Removal 1 min min min min min min Rocky Mount, NC - True Soluble CBOD Removal vs. Aeration Time Raw Soluble CBOD(mg/L) min 25 min 10 5 min 10 min 15 min 20 min 0 Time (minutes)

20 Soluble CBOD Removals Soluble CBOD True Soluble CBOD WWTP B WWTP B Raw Water SCBOD (mg/l) 100 Raw Water SCBOD (mg/l) 52 10' Aerate / Filter 13 10' Aerate / Floc-Filter ' Aerate / Filter ' Aerate / Floc-Filter 7.6 % SCBOD % SCBOD ' Aerate / Jar Test / Filter ' Aerate / Jar Test / Filter ' % SCBOD Removal ' % SCBOD Removal 96.3 % TSCBOD % TSCBOD ' Aerate / Jar Test / Floc-Filter ' Aerate / Jar Test / Floc-Filter ' % TSCBOD Removal ' % TSCBOD Removal 93.3

21 Total CBOD Removals Total CBOD WWTP A WWTP B Day 1 Day 2 Raw Water Total CBOD (mg/l) ' Aerate and Jar Test 10 n/a ' Aerate and Jar Test n/a ' % CBOD Removal 95.2 n/a ' % CBOD Removal n/a

22 Particulate (and colloidal) CBOD Removals Particulate CBOD WWTP A WWTP B Day 1 Raw Particulate CBOD (mg/l) ' Aerate / Jar Test (no Floc-Filter) ' Aerate / Jar Test / Floc-Filter Remaining Particulate CBOD ' % PCBOD Removal ' Aerate / Jar Test (no Floc-Filter) n/a ' Aerate / Jar Test / Floc-Filter n/a 3.5 Remaining Particulate CBOD n/a ' % PCBOD Removal n/a 97.2

23 Soluble CBOD Removals

24 Soluble CBOD Removals

25 CBOD Removals

26 CBOD Removals

27 Comparative SCBOD Removals (Long vs. Short SRT) Time (minutes) WWTP A SCBOD, Raw = 59 mg/l WWTP B SCBOD, Raw = 100 mg/l Long SRT (12-18 days) Short SRT (3-4 days) SCBOD Removals for 2 WWTPs with Different SRTs WWTP A, 12 Day SRT, Raw TSCBOD = 44 mg/l / 18 mg/l (Day 2) WWTP B, 3 Day SRT, Raw TSCBOD = 52 mg/l 35 Soluble CBOD (mg/l) CT MLSS = 0.88 CT MLSS = Time (minutes)

28 Comparative TSCBOD Removals (Long vs. Short SRT) Time (minutes) WWTP A SCBOD, Raw = 59 mg/l WWTP B SCBOD, Raw = 100 mg/l Long SRT (12-18 days) Short SRT (3-4 days) TSCBOD Removals for 2 WWTPs with Different SRTs WWTP A, 12 Day SRT, Raw TSCBOD = 44 mg/l / 18 mg/l (Day 2) WWTP B, 3 Day SRT, Raw TSCBOD = 52 mg/l CT MLSS = 0.88 Soluble CBOD (mg/l) CT MLSS = Time (minutes)

29 Bench-Scale Testing Results Rapid SCBOD reductions were observed during the first five minutes of aeration followed by a decrease in sorption rate. All SCBOD removal curves were asymptotic. Soluble CBOD sorption ranged between 68 and 91%. True Soluble CBOD sorption ranged between 58 and 88% Particulate CBOD reductions ranged between 95 and 99%. Total CBOD reductions were approximately 95%.

30 Bench-Scale Testing Conclusions Initial TSCBOD reductions (< 1 minute) are believed to be due to sorption alone. Subsequent TSCBOD reductions include respiration. Asymptotic TSCBOD removal curves suggest a limit w.r.t. minimum TSCBOD concentrations for a given plant/srt. Contact tank concept is a viable solution for meeting secondary treatment requirements without the need for blending effluents. Settled sludge should be routed back to the head of the aeration basins to complete oxidation of sorbed SCBOD/TSCBOD.

31 Summary of Bench-Scale Results Accepted biological treatment design = Full secondary treatment Bench-scale results show: % Soluble CBOD removal % True Soluble CBOD removal % Particulate CBOD removal % Total CBOD removal. 5. Biological contact system is capable of meeting secondary treatment requirements (30/30 mg/l and 85% removal of TSS and BOD 5 ) without the need for blending. Next step Determine adsorption and substrate utilization constants (K AD and K) for two plants using the bench scale data.

32 Numerical Modeling using Bench- Scale Data

33 Assumptions and Equations (Adsorption) The instantaneous reduction of True Soluble CBOD (TSCBOD) is assumed as adsorption. No oxygen consumption is considered as necessary for this process. The amount of adsorption of TSCBOD on MLSS is proportional to the MLSS concentration and the mixture TSCBOD concentration at equilibrium: TSCBODAD = KAD x TSCBODO x MLSSMIX The TSCBOD in the mixed liquor after adsorption is calculated using the following equation. TSCBODO = TSCBODMIX 1 + (KAD * MLSSMIX)

34 Assumptions and Equations (Substrate Utilization) The slow reduction of TSCBOD between 1 and 25 minutes can be considered as biomass utilization of TSCBOD with oxygen consumption. The reaction rate is modeled as a first-order reaction because: 1. It is simple 2. We are primarily dealing with wet weather flows, which usually have low TSCBOD concentrations. Where: Xo = MLSS conc in contact tank C = SBOD conc after contact tank Co = SBOD conc after adsorption Cmin = Minimum SBOD conc that can be achieved (constant) The reaction is: dc = -kxo (Co - Cmin) dt After integration: C = Cmin + (Co Cmin) exp(-kxot)

35 Numerical Modeling Conclusions 1. Instantaneous BOD reduction is modeled by adsorption (No oxygen is needed) 2. Slow BOD reduction is modeled by substrate utilization by biomass (Need oxygen) 3. Both processes (adsorption and biomass utilization) depend on biomass concentration (represented by MLSS). So, an increase in MLSS will reduce the volume of the contact tank and retention time required. 4. The sludge from short SRT processes (WWTP B) contains more Active Biomass in the MLSS and thus performs better in the contact zone than sludge from long SRT processes (WWTP A). 35

36 Knoxville Pilot Study January May 2010

37 KUB Knoxville Utility Board City has limited capacity to treat wet weather events Pilot studies were conducted at two WWTPs Kuwahee WWTP (30 MGD) o Near University of TN o Some industrial component 4 th Creek WWTP (8 MGD) o Residential area

38 Pilot Protocol Test various MLSS concentrations and system retention times to determine optimum conditions for Soluble BOD and TSS removal Contact tank MLSS varied by addition of conventional plant RAS to raw wastewater & secondary effluent blend Determine parameters required to achieve 85% Total BOD removal, thus meeting requirement of full biological treatment MLSS levels tested from mg/l Retention times tested from minutes (total system) Contact tank subdivided into 5 chambers Either 3 or 5 chambers can be used to allow for varying contact time in the contact tank Coagulant = FeCl3 ( mg/l) Polymer = Hydrex 6112 (Anionic, Dry) (3 4 mg/l) Ballast (microsand) = 134 um, silica

39 Contact Tank & Ballasted Clarification Unit

40 Pilot Unit Set-Up RAW + SECONDARY BLEND RAW WW SECONDARY EFFLUENT RAS FLOW RAW + SECONDARY BLEND

41 Pilot Unit Setup Aerated Contact Tank Drum Screen Air Header

42 AERATED CONTACT TANK

43 BALLASTED CLARIFICATION PROCESS TRAILER COAGULANT DOSE POINT RAW WATER + RAS MATURATION TANK COAGULATION TANK

44 BALLASTED CLARIFICATION PROCESS TRAILER FLOC IN MATURATION TANK MATURATION TANK SETTLED WATER

45 KUWAHEE WWTP PILOT Extended runs conducted at MLSS levels of 400, 800, 1000, 1200, and 1500 mg/l in contact tank Data collected for CBOD, BOD, Floc-filtered CBOD, COD, Floc-filtered COD, and TSS. Influent Total BOD (Raw + Secondary Effluent) was composed of approximately 18% Soluble BOD. Average Influent Total BOD = 161 mg/l. Improved removals noted as contact tank MLSS values increased.

46 RESULTS KUWAHEE WWTP CBOD Removals at 800 mg/l MLSS

47 RESULTS KUWAHEE WWTP CBOD Removals at 1200 mg/l MLSS

48 RESULTS KUWAHEE WWTP CBOD Removals at 1500 mg/l MLSS

49 Kuwahee WWTP MLSS vs TOTAL BOD Removals 300 Avg. Inf. TBOD Avg. Eff. TBOD % Rem. 100 Total BOD (mg/l) % Removal MLSS (mg/l) 0

50 Kuwahee WWTP MLSS vs SOLUBLE BOD Removals 60 Avg. Inf. SBOD Avg. Eff. SBOD % Rem. 100 Soluble BOD (mg/l) % Removal MLSS (mg/l) 0

51 Kuwahee WWTP - Conclusions Total CBOD removals of > 85% were consistently met at MLSS levels of 1000 mg/l and higher in the aeration tank. Removals were not consistently > 85% at MLSS values of 400 and 800 mg/l but were achieved at some points Total BOD removals improved as MLSS levels increased Average Effluent Total BOD values were consistently < 20 mg/l Overall TSS removals were 90% throughout all MLSS levels Ability to meet 85% Total BOD removal is very dependent on Soluble BOD removal As MLSS values increased, removals of Soluble BOD also increased: MLSS AVG INF. SOL. BOD (mg/l) AVG EFF SOL BOD (mg/l) % REMOVAL

52 4 TH CREEK WWTP PILOT Extended runs conducted at MLSS levels of 400, 600, 800, 1000, 1200, and 1500 mg/l in contact tank Data collected for BOD, Floc-filtered BOD, COD, Floc-filtered COD, and TSS. Influent Total BOD (Raw + Secondary Effluent) was composed of approximately 9% Soluble BOD. Average Influent Total BOD = 118 mg/l. Higher RAS flow required to achieve design MLSS due to low Soluble BOD in Raw wastewater Consistently high removals across all MLSS levels

53 RESULTS 4 TH CREEK WWTP BOD REMOVALS AT 400 & 600 mg/l MLSS

54 RESULTS 4 TH CREEK WWTP BOD REMOVALS AT 800 & 1000 mg/l MLSS

55 RESULTS 4 TH CREEK WWTP BOD REMOVALS AT 1200 & 1500 mg/l MLSS

56 4 TH CREEK WWTP MLSS vs TOTAL BOD Removals 300 Avg. Inf. TBOD Avg. Eff. TBOD % Rem. 100 TotalBOD (mg/l) % Removal MLSS (mg/l) 0

57 4 TH CREEK WWTP MLSS vs SOLUBLE BOD Removals 60 Avg. Inf. SBOD Avg. Eff. SBOD % Rem. 100 Soluble BOD (mg/l) % Removal MLSS (mg/l) 0

58 4 TH CREEK PILOT - CONCLUSIONS Total BOD removals of > 85% were consistently met at all MLSS levels Very low soluble BOD present in raw wastewater = excellent Total BOD removals Ballasted clarification process removed almost 100% of Particulate BOD TSS removals of > 90% were achieved across all MLSS levels Average Effluent Total BOD values were consistently < 10 mg/l Improved Soluble BOD removals at MLSS values of 800 mg/l and higher MLSS AVG INF. SOL. BOD (mg/l) AVG EFF SOL BOD (mg/l) % REMOVAL

59 Path Forward EPA has not given blanket approval for this process. Approval to be handled on a plant-by-plant basis Approval to begin design phase for the Knoxville plants First US installation under contract at Wilson Creek, TX Dual Use 1. Tertiary during dry weather for Total P removal 2. Biologically Enhanced HRC mode during wet weather 3. One train at 32 MGD

60 Acknowledgements David Holliman Kruger Clarification Process Hong Zhao Kruger Biological Process Bryan Fincher Kruger Pilot Zach Bobak Kruger Pilot CDM Al Sun, Kati Bell, Josh Norton Plant and Lab Staff at Knoxville WWTPs

61 Questions? Thank you!