Bench-scale assessment of the effectiveness of an anaerobic selector in controlling filamentous bulking.

A laboratory scale sequencing batch reactor (SBR) was used to assess the ability of an anaerobic selector to control filamentous growth in an activated sludge plant experiencing bulking problems. The SBR was operated under a sequence of 60 min anaerobic followed by 120 min of aerobic period at 20 degrees C, with a total solids retention time (SRT) of 4 d and a hydraulic retention time (HRT) of 8 h. The apparent soluble organic carbon (SOC) removal from the liquid phase averaged 18% during the anaerobic period, which is significantly less than the 80-90% removal generally considered to be required to suppress the growth of filamentous bacteria. The anaerobic selector was, however, able to control sludge bulking, resulting in an average sludge volume index (SVI) below 140 ml g(-1). The true amount of the SOC uptake was masked by simultaneous hydrolysis of particulate organic matter during the anaerobic period, a process which should be considered in future studies and comparisons.