Slow Sand Filter Amendments for Clay Removal and Corrosion Control Stephen J. Rooklidge Bioengineering Department Oregon State University June 23, 2003

Outline  Filter Descriptions  Research Origin  Laboratory Experiments  Field Experiments  Summary Objectives Expand Slow Sand Filter use by:  evaluating roughing filter pretreatment  evaluating limestone amendments

Slow Sand and Roughing Filters  “Passive” treatment method  RF/SSF - physical and biological processes  Appropriate for rural regions and developing nations

Limestone Amendments  Two experimental and one EPA-approved limestone amendment positions to alter filter performance and effluent corrosion control  Research filter media materials are basalt, calcite, and dolomite limestone

Research Origins  Slow sand filters of the City of Salem, OR provide drinking water for 155,000 residents from the Santiam River

Research Origins  Santiam River produces filter effluent with pH < 7  SSF were unable to treat water with > 140 ntu clay turbidity during the flood of 1996 turbidity during the flood of 1996

Research Questions  Will roughing filters amended with limestone enhance clay removal?  Will a SSF amended with limestone enhance effluent corrosion control?

Laboratory Experiments Bench-scale RF clay turbidity challenge tests: Compared clay removal of basalt and calcite media Calcium Dissolution 48-minute Detention Ca 2+ (mg/L) BASALT1.55 CALCITE8.42

X-Ray Diffraction Qualitatively examined clay removal using changes in kaolinite and montmorillonite XRD peak area ratios (K/M) Kaolinite ~ 25 o / Montmorillonite ~ 27 o

Clay Removal Trends BASALTCALCITE

Pilot-scale Research  Three RF/SSF configurations: Basalt, Calcite, Calcite-amended Basalt Filter Media  60-day study & 150 NTU clay challenge tests

Roughing Filter Research Results

SSF Corrosion Control Effluent pH decreased by: Microbial activity Microbial activity CO 2 conversion CO 2 conversion Increase effluent pH by: Installing dolomite layer 48 cm from schmutzdecke

Corrosion Control Results  Effluent met OHD pH requirements for majority of 60- day study  Saturation Index, alkalinity, and hardness raised

Mineral Service Life Calculation  Constant flow rate  Filter area  Range of dolomite packed density  Assumption of stoichiometric dissolution CaMg(CO 3 ) 2  Ca 2+ + Mg CO 3 Verified by: EDTA titration hardness EDTA titration hardness vs. vs. Hardness by Calculation Hardness by Calculation (P > 0.12) (P > 0.12)

Effluent Limestone Contactor Research study limestone media acquired from: Ashgrove Rivergate Lime Plant, Portland, Oregon

Contactor Feasibility Decision Tree  Design contactor length using EPA DESCON program Parameters needed: pH pH Alkalinity (DIC) Alkalinity (DIC) Calcium Calcium Iron Iron Manganese Manganese Available at Raymond Letterman’s website

Research Results  Slow sand filters pretreated by calcite-amended roughing filters comply with regulatory requirements for raw water clay turbidity <1 to 150 NTU, while enhancing effluent corrosion control characteristics.  Dolomite-amended slow sand filters enhance effluent corrosion control, and amendment layer service life appears acceptable for engineering applications.  Limestone contactors are an applicable corrosion control engineering design for surface waters of the Pacific Northwest.

Acknowledgements  Environmental & Water Resources Institute (ASCE)  Oregon State University, Dr. J. Ronald Miner  University of Notre Dame, Dr. Lloyd H. Ketchum, Jr.  City of Salem water operations and engineering staff Publications:  Rooklidge, S., Ketchum, L., Burns, P Clay Removal in Basaltic and Limestone Horizontal Roughing Filters. Advances in Environmental Research, 7/1,  Rooklidge, S., Ketchum, L Corrosion Control Enhancement from a Dolomite-amended Slow Sand Filter. Water Research, 36/11,  Rooklidge, S., Ketchum, L Calcite-Amended Roughing Filtration for Clay Turbidity Removal. Journal of Water Supply: Research and Technology- Aqua, 51/6,