PROCESS-CONTROL FACTORS INFLUENCING NOCARDIA POPULATIONS IN ACTIVATED-SLUDGE

Bench-scale activated sludge experiments were conducted on Sacramento, California, primary effluent to determine the effect of various process control factors on Nocardia populations in activated sludge. It was possible to wash Nocardia out 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 increasing Nocardia populations in activated sludge. The optimum pH for Nocardia growth in activated sludge was approximately 6.5. Aerobic selectors were effective in controlling Nocardia at an MCRT of 5 days but not at an MCRT of 10 days. Anoxic selectors controlled Nocardia in a nitrifying activated sludge at an MCRT of 12 days.