The primary degradation of a linear alcohol ethoxylate (AE) and a branched nonylphenol ethoxylate (NPE) was investigated in bench-scale activated sludge units treating a synthetic sewage feed. Biotreaters were gradually adapted to 10-100 mg/ℓ surfactant and effluents monitored for loss of nonionic ethoxylate, foaming, feed BOD removal, nitrification and biosolids growth. Both surfactants were degraded at influent doses of 10-40 mg/ℓ. Substantial BOD breakthrough, loss of nitrification, aerator foaming and incomplete removal of the NPE surfactant occurred when fed at 80 and 100 mg/ℓ while the unit treating AE was unaffected by high surfactant levels. Comparative aquatic toxicity of the biotreated waste at high surfactant levels indicated that the NPE effluent was acutely toxic (EC50, 7-15% effluent) to the fathead minnow and Daphnia while that of the AE unit was non-toxic (EC50, > 100% effluent) to these same species. These studies indicate that the treatment of wastes containing high levels of NPE ethoxylates may adversely impact an activated sludge process in incomplete degradation and foaming, impaired BOD removal, loss in nitrification and the formation of toxic effluents. AE surfactants, however, undergo extensive microbial degradation and cause little or no impact on the activated sludge treatment process.
Modelling the active sludge treatment process in recirculation basins using the simulink environment