RATIONAL BASIS FOR DETERMINING THE DESLUDGING INTERVALS OF SEPTIC TANKS

Abstract

Ability to determine appropriate deshudging intervals will go a long way in maintaining septic tank effluent standards. A relationship between decline in detention time and sludge level was derived and then combined with an already existing empirical sludge accumulation equation. Next, the decline in suspended solids removal efficiency was equated to the decline in detention time. Hence an expression was obtained which relates sludge depth to septic tank effluent suspended solids. Using data from literature, charts were produced which can aid a designer in selecting appropriate detention time and desludging intervals for septic tanks. Results obtained show that a septic tank does not necessarily have to be desludged when sludge reaches one-third of the tank's depth. The depth at which desludging should be done may be less or move depending on the required effluent suspended solids concentration.