Comparing Carbons for Disinfection Byproduct Control. Maggie H. Pierce, EI Sara N. Gibson, PE Mark M. Bishop, PE David S.

Transcription

1 Comparing Carbons for Disinfection Byproduct Control Maggie H. Pierce, EI Sara N. Gibson, PE Mark M. Bishop, PE David S. Briley, PE Water JAM 2010

2 Overview Introduction Considerations for Granular Activated Carbon and Powdered Activated Carbon Finished Water Quality Objectives Operational Impacts Footprint Sustainability Capital Costs Operations and Maintenance Costs Example Case Study Conclusions Questions

3 Water JAM Introduction

4 Stage 2 Disinfectants and Disinfection Byproducts Rule Microbial pathogens, disinfectants, and disinfection byproducts (DBPs) DBP formation can be limited by eliminating organic precursors (dissolved organic carbon, DOC) Best available technology identified as enhanced coagulation or granular activated carbon (GAC)

5 Activated Carbon Highly porous material typically manufactured from bituminous coal Coal is crushed and sized, processed at a low temperature, and a high temperature furnace Organic compounds are adsorbed to the surface of the pores as water interacts with the media

6 Activated Carbon Granular Activated Carbon PowderedActivated Carbon Size 1 millimeter diameter 1 micrometer diameter Location in Treatment Train Downstream or replacement of conventional filtration stage Media Handling Replaced on a 6 month to annual basis Upstream of conventional treatment train Removed as sludge on a daily basis

7 Considerations Finished Water Quality Objectives Operational Impacts Footprint Sustainability Capital Costs Operations and Maintenance Costs Water JAM

8 Finished Water Quality Objectives Benefits can include removal of taste and odor, organics, and future emerging contaminants Organics removal will depend on dosage and contact time, raw water quality, and point of application For GAC, recommend pilot testing and/or rapid small scale column tests For PAC, recommend bench scale testing

9 Finished Water Quality Objectives GAC Pilot Testing Can be run to GAC exhaustion and can assess seasonal variations Can provide key data regarding organics breakthrough over a period of time TOC C/C Carbon A - 10 min Carbon A - 20 min Carbon B - 10 min Carbon B - 20 min Carbon C - 10 min Carbon C - 20 min Carbon D - 10 min Carbon D - 20 min Date

10 Finished Water Quality Objectives PAC Bench-Scale Testing Allows for analysis of different PAC doses, contact times, and manufacturers UV Absorbance (1/cm) PAC Dose (mg/l) Pac 1 PAC 2

11 Operational Impacts GAC Location minimizes large water quality shifts and impacts to other chemicals Once tailored, plant staff have minimal decisions to make Oversee GAC change outs and backwashing No increase in solids production Raw Water Source Rapid Mix Flocculation Sedimentation Clearwell Filtration GAC

12 Operational Impacts PAC Location is more susceptible to water quality shifts Operators must monitor on a daily basis and adjust the PAC dose Bulk bag change outs Increase in solids production PAC Raw Water Source Rapid Mix Flocculation Clearwell Filtration Sedimentation

13 Footprint GAC Truck access for loading and unloading Vessel size dependent on plant flow and desired EBCT Concrete filter beds sizing is more variable 40,000 pound vessel 12 D x 27 H 1 mgd 14 minute EBCT Calgon Carbon

14 Footprint PAC Truck access for loading and unloading Dependent on the PAC dosage and bulk bag changeout Each bag is 4 ft x 4 ft 900 pound bulk bag 6 x 6 x 16 H 15 mg/l 7.2 mgd 30 mg/l 3.6 mgd EnPro

15 Sustainability NC AWWA Water JAMWEA Differs due to application point and ability for reuse GAC removes organics above and beyond the means provided in conventional treatment PAC removes DOC at the front end of the treatment plant Fuel and transport of media required for both Sludge generation and need for disposal transport for PAC

16 Capital Costs GAC Pressure Vessels vs. Concrete Filter Beds Facility structure, pumping, finished water chemicals, standby power, I&C, site access Plant Capacity 1 million gallons per day (mgd) Cost $1.90 per gallon 10 mgd $1.00 per gallon 200 mgd $0.50 per gallon USEPA Capital Cost Curve for GAC; adjusted to 2014 dollars

17 Capital Costs PAC Bulk Bag vs. Silo Dry chemical dosing vs. Slurry mix Systems Special considerations: PAC storage, available contact time NC AWWA Water JAMWEA Capital Costs range from $0.125/gallon to $0.25/gallon

18 Operations and Maintenance Costs GAC Reactivated carbon vs. virgin carbon GAC change-out frequency Desired effluent TOC concentration Design EBCT Estimated by pilot testing and modeling Calgon Carbon

19 Operations and Maintenance Costs GAC DOC, mg/l C/C 0 =50% EBCT = 10 minutes EBCT = 15 minutes EBCT = 20 minutes ,000 10,000 15,000 20,000 25,000 30,000 35,000 40,000 Bed Volumes

20 Operations and Maintenance Costs PAC Similar unit cost for PAC as with GAC Dose and frequency (i.e. seasonal vs. continuous) Impacts on raw water chemical doses No opportunity for reactivation Residuals Management carbonanswers.com

21 Summary Consideration Granular Activated Carbon Powdered Activated Carbon Finished Water Quality Objectives Operational Impacts Capital Costs DOC removal Robust barrier for some emerging contaminants Passive technology minimal water quality shifts Minimal impact to other chemicals added GAC change outs (6 months to 1 year) No solids production Typically more capital costs Concrete filter beds more economical than pressure vessels as capacity increases $0.50/gallon - $1.90/gallon (varies by plant capacity) DOC removal Active technology raw water quality shifts May adsorb other chemicals added at same location Replenish PAC supply (if bulk bag or slurry tank system) Increased solids production May be more capital cost effective at lower flows Bulk systems more economical as capacity increases due to bulk bag requirements of other systems $0.125/gallon - $0.25/gallon

22 Summary Consideration Granular Activated Carbon Powdered Activated Carbon O&M Costs Footprint Sustainability Lower operational complexity GAC change out or regeneration costs Power for intermediate pumping (if applicable) Backwash water Determined by plant flow and EBCT Truck access Removes finished water DOC Can be reused Fuel and transport for regeneration Operator monitoring of DOC to assess PAC dose Routine maintenance of mixing equipment and metering pumps (if applicable) Residual management PAC bulk bags or media Possible increased dose of other chemicals at application point Determined by plant flow and PAC dose Truck access Removes raw water DOC One-time use of media Fuel and transport for delivery Sludge production and disposal to landfill (or other location)

23 Water JAM Example Case Study

24 Case Study NC AWWA Water JAMWEA MGD Drinking Water Treatment Plant in the MidAtlantic Stage 2 D/DBP Compliance evaluation comparing five advanced treatment technologies, including GAC Compared based on seven different criteria. Miexresin.com xylem.com Southern Outer Banks WTP

25 Case Study Finished Water Quality Goals No LRAA Violations No OEL exceedances DBP Concentrations < 80% of the MCL GAC Column Test NC AWWA Water JAMWEA TOC Breakthrough at C/C0=0.80

26 Case Study Hybrid Analysis Model Allison Reinert Hazen and Sawyer Max TOC Breakthrough (mg/l) 0.8 Treatment Flow for GAC (MGD) 9 Number of GAC Reactors 9 Option 2-12 Month Change Out Schedule max Predicted TOC (mg/l) 1.38 Option 2-12 Month Change Out Schedule min Predicted TOC (mg/l) 0.28 Option 2-12 Month Change Out Schedule max THM (ug/l) 97 Option 2-12 Month Change Out Schedule min THM (ug/l) 14 Option 2-12 Month Change Out Schedule max THM LRAA 69 Option 2-12 Month Change Out Schedule min THM LRAA 37 Option 2-12 Month Change Out Schedule max THM OEL 76 Option 2-12 Month Change Out Schedule min THM OEL 34 Option 2-12 Month Change Out Schedule # of Violations of THM LRAA 0 Option 2-12 Month Change Out Schedule # of Violations of 80% THM LRAA 1 Option 2-12 Month Change Out Schedule # of Violations of THM OEL 0

27 Case Study Implementation Schedule and Compliance Deadline did not align PAC Dosage Screen May UV Absorbance (1/cm) PAC Dose (mg/l) Carbon 1 Carbon 2

28 Case Study 14 Day -SDS Disinfection By-Products May Raw TOC: 1.6mg/L TOC (mg/l), TTHM & THAA (ug/l) No PAC 30 min 60 min 30 min min TOC TTHM THAA

29 Case Study Other Considerations: NC AWWA Water JAMWEA Type of PAC feeder Location Sludge Handling Zero discharge WTP Waste EQ, thickeners, belt filter press, supernatant recycling

30 Water JAM Conclusions

31 Conclusions NC AWWA Water JAMWEA Activated carbon is a viable option for Stage 2 D/DBP Compliance GAC vs PAC is based on specific WTP characteristics as well as treatment goals Additional water quality benefits may be realized

32 Acknowledgements David Briley, P.E. Hazen and Sawyer Mark Bishop, P.E. Hazen and Sawyer Allison Reinert, E.I. Hazen and Sawyer Bret Casey, P.E. Hazen and Sawyer

33 Questions? Maggie Pierce, E.I. Sara Gibson, P.E. Water JAM