ABSTRACT:
Bench‐scale activated sludge experiments were conducted on Sacramento, California, primary effluent to determine the effect of various process control factors onNocardiapopulations in activated sludge. It was possible to washNocardiaout from activated sludge at a sufficiently low MCRT. The washout MCRT for bench‐and full‐scale activated sludge plants was related to the temperature by the Arrhenius equation. Foam trapping was shown to be a major factor in increasingNocardiapopulations in activated sludge. The optimum pH forNocardiagrowth in activated sludge was approximately 6.5. Aerobic selectors were effective in controllingNocardiaat an MCRT of 5 days but not at an MCRT of 10 days. Anoxic selectors controlledNocardiain a nitrifying activated sludge at an MCRT of 12 days.