A dual media filtration study was carried out at the central Weber Wastewater Treatment Plant in Ogden, Utah, to evaluate its feasibility as a tertiary treatment to meet new effluent quality standards. A review of the literature indicated that dual media filters were more efficient than conventional single media sand filters because of the “in depth” filtration achieved by dual media filters. An experimental filter was operated at four different hydraulic loading rates, ranging from 3 to 6 gpm/ft 2 (122.10 to 244.20 1/min/m2), to evaluate its effects on effluent quality. Hydraulic loading rate was shown not to affect suspended solids removal. The experimental filter produced excellent suspended solids removal; however, BOD5 removal efficiency was relatively poor because the influent to the filter contained high concentrations of soluble BOD5 and colloidal organic solids. Filter effluent quality met State of Utah standards of 10 mg/1 of BOD5 at the hydraulic loading rate of 3 gpm/ft2 and exceeded the standard by less than 2 mg/1 at loading rates due to removal of 4, 5, and 6 gpm/ft2. Filter cycle durations were very short at higher filtration rates due to removal of influent suspended solids in the intermixed portions of the filter media. Biological growth within the filter media was a major problem in the operation of the filter. The filter influent was chlorinated to prevent this growth. The study indicated that dual media filtration of trickling filter plant effluent to meet new effluent quality standards is economically feasible and can produce an effluent which meets state and federal standards.
Dawda, Madhusudan M.; Davidson, M. L.; and Middlebrooks, E. J., "Evaluation of the Addition of Granular Media Filtration to Wastewater Treatment Plants to Meet New Standards" (1976). Reports. Paper 516.