Detention Time as a Critical Parameter in Septic Tank Design

Abstract

In order to reveal the importance of detention time in septic tank design, an expression was derived to show the relationship between detention time and sludge level. Charts that show the decline of detention time with sludge accumulation were produced. These charts show that the usual recommendation that septic tanks be desludged when they are one-third full could be irrational most of the time. It was shown that a tank that is one-third full may still have enough residual detention time for optimal performance. A more rational approach is that septic tanks should be desludged when they no longer have enough detention time for efficient performance. It was also shown that water use should be given serious attention in septic tank design as it can have serious consequences for detention time.