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After almost fifty years of service, the City of Ukiah's Wastewater Treatment Plant (WWTP) began to show indications it was operating at capacity. Engineering planning and design work began in December 2002 to replace the now dated technology of the original facilities and rehabilitate and expand the rest of the WWTP to meet current and future discharge requirements. Finding ways to increase process capacity until the new facilities are completed became of paramount importance.

A study was completed in 2003 to determine the WWTP's process capacity. The results of this study verified that the WWTP was at capacity and was primarily limited by its process capacity, particularly soluble BOD removal capacity. Following the plant capacity analysis, a brainstorming session was held to discuss methods to increase capacity in the interim until WWTP improvements could be completed to increase capacity. Chemically enhanced primary treatment (CEPT) with ferric chloride and polymer additions near the influent of the aerated grit tanks showed the most promise with an increase in BOD removal of 15 percent to 20 percent. Another method that is helping the WWTP meet its permit limits is the use of the AWT facility during the period from May 15th to September 30th when the WWTP can only discharge to three evaporation/percolation ponds.

As a result of the study and brainstorming session, procedural and operational changes were made that increased the plant's interim capacity. The additional capacity has allowed the Ukiah City Council to lift the restrictions on the sale of new sewer connections and avoid future restrictions and moratoriums until the WWTP improvements are completed in October 2008.
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Document Type: Research Article

Publication date: 2005-01-01

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