Biological Treatment for Hexavalent Chromium at the City of Davis

Transcription

1 Biological Treatment for Hexavalent Chromium at the City of Davis Water Resources Association of Yolo County Board of Directors Meeting Presenter: Sarah Laybourne & Tim Williams Kennedy/Jenks Consultants June 10, 2013 Sacramento, CA

2 Key Contributors City of Davis Jacques DeBra Dianna Jensen Marie Graham Gary Wells Envirogen Todd Webster Sam Wong Kennedy/Jenks Lynn Takaichi Tim Williams Joe Drago Sean Maguire Sarah Laybourne

3 Project $150k SWRCB Cleanup and Abatement Program Water Resources Association of Yolo County Sacramento Groundwater Authority City of Davis

4 Background: Regulations Currently CA MCL of 50 µg/l for Total Chromium No specific MCL for Hexavalent Chromium Federal MCL for Total Chromium of 100 µg/l California set PHG for Cr6 of 0.02 µg/l (2011) Cr6 PHG triggered process for setting MCL for Cr6

5 CDPH Regulatory Schedule for Cr6 MCL Propose MCL in July 2013 Expected proposed MCL between 2-25 µg/l Proposed MCL must be achievable Benefit-cost analysis considered to assess risk reduction Impact on small systems (< 200 connections) considered Final regulation within next three years

6 Chromium 6 Occurrence in Sacramento Area

7 Existing Treatment Technologies for Cr6 Removal Strong base anion exchange (SBA) Weak base anion exchange (WBA) Reduction coagulation filtration (RCF)

8 Why Biological Treatment Promising emerging technology for drinking water Capable of addressing multiple contaminants Chromium 6 Nitrate Perchlorate (BAT) Selenate Uranium

9 Biological Process Electron donor Acetic acid O 2 NO 3 - ClO 4 - CrO 4 2- HSeO 4 - Bacteria CO 2 + H 2 O N 2 Cl - Cr 3+ HSeO 3 - Nutrient Phosphoric acid Excess bacteria (cell growth)

10 Pilot Study: Conceptual Design Diagram

11 Pilot System

12 Biological FBR in Action

13 Analytical Results Chromium-6

14 Analytical Results Total Chromium

15 Analytical Results Nitrate

16 Analytical Results Selenium (spiked with selenate)

17 Analytical Results Chromium-6 Filtration & Disinfection (1.5 mg/l chlorine dose)

18 Analytical Results Total Chromium Removal with Coagulant Addition

19 Footprint & Equipment Site Q=2.0 MGD 0.14 Ac site 0.5 Ac site

20 Footprint & Equipment Q=2.0 MGD 0.14 Ac site 0.3 Ac site

21 Existing Full Scale System (Perchlorate Treatment) West Valley WD

22 Water Research Foundation Study WR Foundation took water from 11 agencies to pilot three chromium-6 removal processes Regenerable SBA Exchange Disposable WBA Exchange RCF City of Davis participated with Well 20 water All three systems were successful for removal of chromium-6 WBA was the most expensive system due to disposal requirements and ph adjustment

23 Waste Disposal Requirements Treatment System SBA RCF Option 1 Disposal Assumptions Chromium-6 in the brine is reduced and then removed through clarification. Brine hauled offsite and sludge disposed as CA non- RCRA hazardous waste. Direct discharge of the untreated waste backwash water to the sewer. RCF Option 2 WBA Biological FBR De-watering of backwash water with disposal of the dewatered solids as CA non-rcra hazardous waste. Disposal of resin as a TENORM Hazardous Waste Discharge of clarified backwash water to WTP headworks & about 1% solids discharged directly to the sewer.* * Further analysis of residuals necessary to determine if any waste classification applies.

24 Cost Comparison Annualized Cost Analysis Greenfield Alternative Treatment Cost Comparison Note: WR Foundation costs were normalized and adjusted to be more comparable to the analysis conducted for this study.

25 Next Steps Evaluate any scale-up issues Determine required acclimation periods between temporary and/or long term shutdowns Evaluate impacts of chlorine addition, including reformation potential of chromium-6 and formation of disinfection byproducts Confirm effective filter coagulants and dosages Estimate filter backwash and solids content

26 Next Steps Evaluate options for onsite residual management and disposal compared with discharge to sewer Evaluate system for enhanced selenium reduction Test system per CDPH requirements to obtain Best Available Technology (BAT) approval Refine fabrication, construction, and operating costs Develop BAT application criteria

27 Questions & Contact Information Contact: Tim Williams or (916) Sarah Laybourne or (916)

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29 Additional Slides

30 SBA Source: WQTS. Probable Capital and Annual Operations & Maintenance Costs for Hexavalent Chromium Removal from Well 20 Technical Report. April 22, 2013.

31 WBA Source: WQTS. Probable Capital and Annual Operations & Maintenance Costs for Hexavalent Chromium Removal from Well 20 Technical Report. April 22, 2013.

32 RCF Source: WQTS. Probable Capital and Annual Operations & Maintenance Costs for Hexavalent Chromium Removal from Well 20 Technical Report. April 22, 2013.

33 Biological Process Biological process in drinking water in CA requires Use of indigenous microbes Post Aeration if anoxic Filtration Disinfection Biological Fluidized Bed Reactor (FBR) is Best Available Technology (BAT) for perchlorate in CA

34 Motivation for Study Evaluate effectiveness of concurrently removing multiple contaminants: Evaluate residual management impacts and management options Evaluate co-removal potential of nitrate, selenium and perchlorate Prove efficacy of an alternative technology to others already studied: Weak and strong base anion exchange Reduction, coagulation, and filtration Evaluate the potential for disinfection to convert any remaining chromium 3 to chromium 6 Compare results with the WRF Project 4450 Impact of Water Quality on Cr6 Removal Efficiency & Costs

35 Biological Filtration - Fluidized Bed Reactor Fluidized Granular Activated Carbon (GAC) bed Chemical Feed State NSF 60 Approved Acetic Acid Electron Donor Phosphoric Acid Nutrient Mix Nitrate is the main electron acceptor 8-9 mg/l Nitrate as N µg/l chromium as chromium 6 Anoxic environment to grow denitrifying and chromium reducing bacteria Co-reduction of nitrate and chromium 6 Testing at 4 different Hydraulic Residence Times (HRT): 60, 40, 20, & 15 Minutes Other potentially treated constituents Selenium Perchlorate

36 Pilot System

37 City of Davis Well 20 Pilot water source

38 Pilot Booster Pump Station

39 Well 20 Water Quality Total Chromium: µg/l* Hexavalent Chromium: µg/l* Nitrate-N: mg/l* Selenium: <2.0-4 µg/l** * Measured during Pilot Study ** City Historical data from Water Quality Sampling for the period of

40 Influent and Effluent TOC

41 Summary of Results

42 Footprint & Cost Estimates Based on Q = 2.0 MGD Specific Site Modify well pump & motor One FBR & Two Aeration Tanks Contact Tank for Coag Mixing Two Press Filters Filter BW Tank + BPS + Sewer Discharge Greenfield Site Well in place Optimize Treatment One FBR & One Aeration Tank Inline mixing of coag CT achieved w/filters Filter 5.0 vs. 3.0 gpm/sf BPS outside

43 Findings - Comparison of Results with Project Objectives # Objective Findings and Conclusions 1 Confirm whether a biological treatment system may provide an effective means of chromium-6 treatment (1) System appears effective to reduce chromium-6 and remove a fraction of the total chromium. 2 Confirm efficacy and cost effectiveness of treating chromium- 6 to low levels (less than 1 µg/l) (1) Effective chromium-6 reduction to concentrations less than 1 µg/l is achievable. (2)TOC residual could present water quality challenges (DBP) for achieving effluent chromium-6 below 1 µg/l. (3)The annualized construction cost range is $232 to $281 per acre foot.

44 Findings - Comparison of Results with Project Objectives # Objective Findings and Conclusions 3 Evaluate effectiveness of removal of multiple constituents (nitrate, selenium, perchlorate, chromium-6) (1) Effective removal of nitrate-n to below 2 mg/l. Average removal 95%. (2) Removal of chromium-6 with filtration below 5 ug/l. Average reduction 91%. (3) Average removal of selenium 70%. (4) Perchlorate removal has been demonstrated at full-scale level. 4 Evaluate relationship between chromium-6 and total chromium, and potential impacts to the distribution system (1) 35% of the chromium-6 reduced to chromium-3 was present in a dissolved form. (2)Addition of ferric chloride increased total chromium removal from 65% to 90%. (3)Disinfection tests showed 16-18% reformation of chromium-6

45 Findings - Comparison of Results with Project Objectives # Objective Findings and Conclusions 5 Evaluate residual management impacts and options (1) Backwash waste solids will ideally be discharged to a sewer. (2) Further investigation is necessary. 6 Evaluate pilot study results with the WR Foundation Projects analysis for the City of Davis (1) FBR may be more costly than the SBA in capital. (2) FBR may be comparable to the capital cost for the RCF. (3) Initial analysis indicated that FBR O&M cost may be the lowest. (4) FBR, SBA and RCF were in the same order of magnitude for costs.