Pilot plant studies were conducted on domestic wastewater to determine the feasibility of replacing or augmenting conventional activated sludge gravitational clarifiers by dynamic straining. This work was a continuation of the successful program accomplished under EPA report numbered PB-242 848. In the prior program, two dynamic strainers in series were employed. In this program, less expensive techniques for polishing the primary strainer effluent were investigated. Phase I covered pilot operations with the strainer in the aeration tank of an activated sludge plant producing a nitrified effluent. Phase II involved a non-nitrified effluent. In both phases, upflow and downflow sand filtration, settling, and flocculation-settling of the strainer effluent were investigated. Phase I flows were low but correlated well with the previous studies of strainer operating variables. Strainer effluent averaged 35 mg/l suspended solids with mixed liquor suspended solids (MLSS) of 6800 mg/l. The upflow and downflow sand filters, operating on strainer effluent, produced effluents of 8 and 3 mg/l suspended solids, respectively. Phase II, which called for high flows and high BOD loadings, was plagued with an intense growth of filamentous microorganisms, foaming, and development of a 'syrupy' mixed liquor. Proper strainer throughputs could not be maintained. Flow rates were not reproducible and did not correlate with prior work.

"June 1978." Includes bibliographical references (page 42). U.S. Environmental Protection Agency Contract No. Contract Number: 68-03-0427, Program Element No. 1BC611, SOS#3, Task D-1/21.