Unified basis for design of biological aerobic treatment processes

Abstract

Equations are presented for the design and operation of aeration tanks with plug flow and complete-mixing patterns and of trickling filters without and with recirculation. Three dimensionless numbers are the common basis of all the mathematical representations. Coefficients in the equations were computed from data measured in various sewage treatment plants. Mean square deviations were 3·3 per cent for the efficiency and 5·3 mg I−1 for BOD, in secondary effluents with plug flow pattern aeration tanks and, respectively, 3·2 per cent and 7·2 mg I−1 with complete-mixing aeration tanks. Linearization of the equations led to the correlation coefficients of 0·998 for plug flow and 0·936 for complete-mixing patterns. It follows from the equations that, under the same conditions, treatment efficiencies are higher in complete-mixing tanks than in plug flow ones, and that there does not exist a single-valued relationship between the treatment efficiency and sludge load. The type of equation applied for activated sludge process with plug flow pattern fits also trickling filters. Examples are given of the design of aeration tanks with different flow patterns and trickling filters.