Slow Sand Filter Amendments for Clay Removal and Corrosion Control

1
Slow Sand Filter Amendments forClay Removal and
Corrosion Control
Stephen J. Rooklidge Bioengineering
Department Oregon State University June 23, 2003
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Outline

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

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Slow Sand and Roughing Filters

• Passive treatment method
• RF/SSF - physical and biological processes
• Appropriate for rural regions and developing
  nations

4
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

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Research Origins

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

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Research Origins

• Santiam River produces filter effluent with pH
  lt 7
• SSF were unable to treat water with gt 140 ntu
  clay
• turbidity during the flood of 1996

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Research Questions

• Will roughing filters amended with limestone
  enhance clay removal?
• Will a SSF amended with limestone enhance
  effluent corrosion control?

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Laboratory Experiments

• Bench-scale RF clay turbidity challenge tests
• Compared clay removal of basalt and calcite media
  

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X-Ray Diffraction

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

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Clay Removal Trends

• BASALT
• CALCITE

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Pilot-scale Research

• Three RF/SSF configurations
• Basalt, Calcite, Calcite-amended Basalt Filter
  Media
• 60-day study 150 NTU clay challenge tests

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Roughing Filter Research Results
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SSF Corrosion Control

• Effluent pH decreased by
• Microbial activity
• CO2 conversion
• Increase effluent pH by
• Installing dolomite layer
• 48 cm from schmutzdecke

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Corrosion Control Results

• Effluent met OHD pH requirements for majority of
  60-day study
• Saturation Index, alkalinity, and hardness raised

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Mineral Service Life Calculation

• Constant flow rate
• Filter area
• Range of dolomite packed density
• Assumption of stoichiometric dissolution
• CaMg(CO3)2 ?
• Ca2 Mg2 2CO3
• Verified by
• EDTA titration hardness
• vs.
• Hardness by Calculation
• (P gt 0.12)

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

• Design contactor length using EPA DESCON program
• Parameters needed
• pH
• Alkalinity (DIC)
• Calcium
• Iron
• Manganese
• Available at Raymond Lettermans website
  http//web.syr.edu/rdletter/

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Research Results

• Slow sand filters pretreated by calcite-amended
  roughing filters comply with regulatory
  requirements for raw water clay turbidity lt1 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.

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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. 2002.
  Clay Removal in Basaltic and Limestone Horizontal
  Roughing Filters. Advances in Environmental
  Research, 7/1, 231-237.
• Rooklidge, S., Ketchum, L. 2002. Corrosion
  Control Enhancement from a Dolomite-amended Slow
  Sand Filter. Water Research, 36/11, 2689-2694.
• Rooklidge, S., Ketchum, L. 2002.
  Calcite-Amended Roughing Filtration for Clay
  Turbidity Removal. Journal of Water Supply
  Research and Technology- Aqua, 51/6, 333-343.