Responses of activated sludge to an increase in phenol loading

The limit of phenol-loading rate for an activated-sludge process was predicted to be 4 g/l, d, based on kinetic data for the phenol-oxygenating activity of activated sludge treating phenol at a loading rate of 0.3 g/l, d. However, the activated-sludge process broke down 5 d after increasing the loading rate from 0.3 to 2.0 g/l, d. One day before the breakdown, the phenol-oxygenating activity of the activated sludge suddenly decreased, coupled with the occurrence of DOC (dissolved organic carbon), suggesting that these events may have caused the breakdown.