Two multi-chamber settling tanks were analyzed to det. the effect of the no. of chambers for contaminant removal from domestic sewage. An increase in the chamber no. from 2 to 4 did not result in any improvement of the removal efficiency. The biol. O-2 demand, COD, no. of coliforms (including fecal coliform) as well as total suspended solids, N and total P were even markedly higher after pretreatment in the 4-chamber settling tank than after pretreatment in the 2-chamber one.