In-sewer fixed screening of combined sewer overflows

Field sampling and measuring were conducted in conjunction with laboratory investigations on the characterization of combined sewage and the effects of solids removal on chlorination practices. Sixty combined sewage bulk samples and 60 combined sewage screenings samples retained on screens of 0.125-, 0.25-, 0.5-, and 1.0 in. aperture were analyzed and evaluated. Removals of deoxygenating materials, oils and greases, and bacteria by fixed screens placed in combined sewers were marginal. Reductions in chlorine requirements as a result of prior solids removal by fixed screening appear small. Screens with aperture sizes ranging from 0.0164 to 1.0 in. appear to have very little effect on bacterial concentrations.