Control of bulking sludge caused by Type 021 N and Type 0961 in an industrial wastewater treatment plant with an aerobic selector.

Over a period of 6 months, pilot plant investigations were carried out with the purpose of bulking sludge control with different aerobic selectors. The wastewater was dominated by industrial dischargers, containing volatile fatty acids up to 450 mg/l. With complete-mix-selectors it was not possible to achieve a stable SVI below 150 ml/g. The bulking sludge could only be controlled with a sectionalized selector (HRT 5-8 minutes per section). The SVI decreased to values below 100 ml/g. Shock-loads and increased VFA-concentrations (by dosing NaC2H3OO) did not cause filamentous growth.