Pilot Study Application of Tertiary Clarification and Filtration to Meet Proposed Ultra Low Phosphorous Discharge Limits on The Spokane River

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The Spokane River flows through northern Idaho and eastern Washington. The Washington State Department of Ecology is proposing to implement an interim phosphorous TMDL (total maximum daily load) of 50 ppb, and a final TMDL of 10 ppb on all point source discharges to the river. Biological treatment alone is not sufficient to meet these levels, requiring the addition of tertiary physical/chemical treatment to existing systems. One treatment method available is co-precipitation by coagulation, clarification and filtration.

Pilot studies were conducted on a municipal and industrial wastewater source that currently exceed the proposed TMDL. At each site two treatment processes were investigated. Process Train 1 utilized up-flow buoyant media clarification followed by mixed media filtration. Train 2 was comprised of a three stage process combining high rate sedimentation ahead of Train 1. Chemical treatment focused on co-precipitation with aluminum sulfate or ferric chloride and polymer addition.

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