A 75 MGD combined sewer overflow treatment facility was constructed to obtain plant-scale data on the effectiveness and costs of screening combined sewer overflows (CSO) by three types of fine screens. The methods of screening evaluated included fixed side hill screens, rotary centrifugal fine screening, and horizontal rotary drum fine screening. Also evaluated were the benefits to the receiving waters by pollutant removal by screening, chlorination, and ponding previously by-passed CSO. Each of 38 separate CSO events were analyzed over a 13-month period commencing in January, 1975 for 14 pollutant parameters and flow rates. None of the screening methods studied have removal efficiencies for suspended solids, BOD5, COD and nutrients that were significantly different from zero at the 95% confidence level. No effect between hydraulic loading and removal efficiency was found. The least overall cost method of screening was the fixed vertical-type screen. All the screens studied have hydraulic head requirements on the order of 2 to 10 feet static loss. The two-day terminal pond following screening was shown to be capable of meeting 30 mg/l of BOD5 and suspended solids 95 percent of the days studied over the 4-year evaluation period.

Issued Aug. 1979. Includes bibliographical references (page 124). Prepared by Howard Needles Tammen & Bergendoff, and City Utilities, Water Pollution Control Plant, Fort Wayne, Indiana, under grant no. Contract Number: 11020 GYU.