MAXIMIZING SECONDARY WET WEATHER TREATMENT CAPACITY AT A NORTHWEST CSO FACILITY

摘要

The Columbia Boulevard Wastewater Treatment Plant (CBWTP) is the largest treatment plant inrnthe State of Oregon, treating an average day flow of 66 mgd. The collection system includesrnboth a combined system and separated sanitary system. Portland’s combined storm and sanitaryrncollection system has necessitated the City to explore strategies to reduce combined sewerrnoverflows (CSOs) including the installation of 13 miles of large diameter pipe to collect andrnstore combined sewage during rain events. Captured CSO~1 and combined sewer system flows asrnhigh as 450 million gallons per day can be conveyed to the CBWTP for treatment and the Cityrnaims to maximize wet weather flows receiving secondary treatment. However, high sludgernvolume index (SVI) values, lack of wet weather operating modes and inadequate process controlrnfunctionality limit the capacity of the secondary process. Secondary treatment is further limitedrnby the existing shallow, peripheral feed secondary clarifiers. A project is currently underrnconstruction to address the short-comings of the existing secondary system and provide up-todaternprocess control technology. The process design includes multiple wet weather operatingrnmodes to address the rapidly changing, diverse character of the wet weather flow conditionsrnexperienced at the CBWTP. This paper will summarize the process design and control systemrnfunctionality that will maximize secondary capacity while maintaining sludge settleability duringrnwet weather events.