The effect of withdrawal of morpholine from the influent and its reinstatement on the performance and microbial ecology of a model activated sludge plant treating a morpholine‐containing influent

An activated sludge plant was established which was capable of treating an influent containing morpholine. When this compound was deleted from the influent the ability of the activated sludge to degrade morpholine was reduced. This reduction took the form of an increase in the length of the lag period before morpholine degradation was detected in a die‐away test from 0 to ca 1000 h. The decreased ability of the activated sludge to degrade morpholine was accounted for by a decline in the specific population of morpholine‐degrading microbes. In this activated sludge all morpholine degraders were Mycobacterium spp. In the absence of morpholine in the influent most mycobacteria in the activated sludge retained their morpholine‐degrading phenotypes. This is despite the fact that some of these organisms can lose this phenotype when grown under non‐selective conditions. These results are discussed in relation to other work on the degradation of morpholine and to problems in the treatment of xenobiotic compounds in industrial effluents.