Municipal Tertiary Filtration
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Plant History: The wastewater treatment plant has operated for many years as a lagoon treatment process. Over the years, with tightening discharge requirements, it became necessary to filter the final lagoon discharge to meet these more strict permit requirements of reduced phosphorus and solids levels.
Plant Description: The facility operates as a five-stage lagoon operation. The operators have aeration capability in the first four ponds. The plant flow rates vary during the year with average flows being in the 230,000 gallon per day range with peak flows being up to 300,000 gallons per day. Alum addition is currently being injected at the head of Pond 4. The addition of alum is to enhance the precipitation process of phosphorus in the ponds. The feed to the tertiary filters flows by gravity to an effluent pump station and then regulated to the Centra-flo Filter. From the filter system the flow proceeds to the UV disinfection and flow measuring before final discharge.
Tertiary Filters: The Centra-flo Gravity Sand Filter Model CF-50 with two (2) airlift units in a single tank. The system is designed to remove algae and suspended solids as well as reduce the phosphorus levels from the plant discharge stream. The plant has the ability to add chemicals to aid in the removal of solids before Pond 4 and also immediately prior to the filter unit. By design, the reject from the filter carries the alum dosage back to the head of Pond 4. Currently the phosphorus levels in the filter feed are approximately 2.0 mg/l with the filtrate from the filter being less than 0.8 mg/l. These values are expected to improve. The new discharge permit requirements state that the phosphorus levels must be below 1.0 mg/l P or there can be no flow from the facility.
Filter Startup: The Centra-flo was installed in July 1999. Equipment startup was completed and the filter system was put online in October of 1999. The filter has been in continuous operation since startup at a flow rate 145 gpm. The operation has been uneventful with only normal operator attention required.