PREDICTION OF THE O-2 CONDITIONS IN THE SELECTOR

Influent characterization and biosorption experiments were carried out with settled influent of seven wastewater treatment plants to study t he influence of O-2 in the selector in relation to the success of deve loping good settling properties of the sludge. In previous years worki ng selectors were installed and/or pilot plant research was carried ou t at these wastewater treatment plants. Characterization of the influe nt was done with help of standard COD and BOD measurements with help o f a coarse filter. The research has elucidated that the presence of O- 2 in the selector, at initial sludge loadings of 3.5-6.5 kg BOD/kg MLS S.d., is important for producing good settling properties of the sludg e when the sum of readily biodegradable COD and rapidly hydrolysable C OD is greater than 40%. When the sum of sludge COD and slow hydrolysab le COD is greater than 50% an unaerated selector can be used.