Back to the Basics Challenges and Solutions for Small SystemsGroundwater Treatment Arsenic Lisa Miller Water Quality Engineer Golden State Water Company Agenda Arsenic Overview Federal MCL amp State MCL ID: 768540
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Back to the Basics: Challenges and Solutions for Small Systems/Groundwater Treatment Arsenic Lisa Miller Water Quality Engineer Golden State Water Company
Agenda Arsenic Overview Federal MCL & State MCL BAT Artesia System overview & wells affected by arsenic Types of treatment utilized Coagulation/filtration Adsorptive Media Challenges & Issues Pilot Studies
Arsenic in California Federal MCL – 10 µg/L Effective January 2006 California MCL – 10 µg/L Effective November 2008 Health Effects include cancer, skin damage, circulatory problems, etc. Natural and manmade sources
Arsenic in California Arsenite (As III) vs. Arsenate (As V) Arsenate more readily removed Arsenite can be converted to arsenate by the addition of an oxidant
Arsenic in California Best Available Technology Activated Alumina Coagulation/Filtration* Ion Exchange Lime Softening* Reverse Osmosis Electrodialysis Oxidation/Filtration *Not BAT for system <500 service connections
Artesia System 10,827 service connections 48,308 population Groundwater System Seven active wells, three with arsenic treatment Co-occurring contaminants Manganese and/or Iron
Coagulation/Filtration Centralia Well #6 Plant effluent arsenic: 5-6 µg/L
Coagulation/Filtration Treatment process involves co-precipitation and adsorption/filtration of iron, manganese, and arsenic Sodium hypochlorite and ferric chloride are injected into raw water Dual media anthracite/sand filters
Coagulation/Filtration Centralia Well #6 Design Capacity 2000 gpm 3 gpm /ft ² Filtration rate Ferric chloride dose: ~4-6 mg/L10 year Media life
Coagulation/Filtration Filters are backwashed every 24 hours of run time Backwash water allowed to settle Decant is recycled to head works
Treatment Considerations Waste Disposal considerations Sludge Hauling Hazardous waste characterization Sewer connection
Pilot Studies Centralia Wells 3 & 4 Advanced Processes for Simultaneous Arsenic and Manganese Removal (2006 AwwaRF Tailored Collaboration Project) Purpose was to modify, demonstrate and optimize an existing treatment process to simultaneously remove As and Mn Establish efficient design process approach for utilities
Pilot Studies Determined that ferric chloride could be added to oxidation/filtration to successfully remove arsenic Ferric chloride doses between 2 and 4 mg/L could reduce arsenic down to 8 µg/L, and higher doses could bring arsenic to ND levels
Adsorptive Media Hawaiian Well #1 and Massinger Well #1 Plant effluent arsenic: typically ND
Adsorptive Media Oxidation/filtration through pyrolusite media Followed by Granular Ferric Oxide adsorption for arsenic removal
Adsorptive Media Hawaiian Well #1 and Massinger Well #1 both 600 gpm each 8 gpm /ft ² filtration rate GFO media does not need to be backwashed
Treatment Considerations GFO is single-pass media Waste Disposal considerations – spent media disposal Media life – lack of bed volumes
Pilot Studies Hawaiian & Massinger treatment alternatives Modifications to the existing adsorption system Hydraulic improvements Vessel cycling Lead-lag vessel configuration pH depression Other adsorptive medias
Pilot Studies Hawaiian & Massinger treatment alternatives Modifications to existing oxidation filtration system Ferric Chloride addition Residuals Handling pH depression Piloted addition of ferric chloride prior to manganese dioxide filters to simultaneously remove manganese and arsenic to eliminate need for GFO
Pilot Studies Century Well #1 AwwaRF Demonstration of Emerging Technologies for Arsenic Removal, Volume 2: Pilot Testing Tested 4 different types of adsorptive media Aluminum-based sorbent Granular ferric hydroxide Iron-coated activated alumina High porosity granular activated alumina
Pilot Studies Conclusions from Century Testing Iron-based media has greater capacity for removing arsenic than alumina media GFH performed better because of higher iron content GFH treated higher volumes of water before breakthrough
Conclusion Coagulation/Filtration successfully removes arsenic, iron, and manganese in one treatment process. Produces waste residuals. Adsorption is a straightforward process to remove arsenic. Media is typically single pass. Type of treatment and success of treatment can vary depending on site specific factors and source water quality. Pilot testing helps determine what will work best for each plant site.
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