The Effect of Anaerobic Selectors on Nocardioform Organism Growth in Activated Sludge

Abstract

Laboratory‐ and full‐scale experiments were conducted to investigate the use of anaerobic selectors for control of nocardioform organisms in activated sludge. The laboratory‐scale, anaerobic‐selector, activated‐sludge system, which exhibited enhanced biological phosphorus removal (EBPR) at a 2.4‐day total mean cell retention time (MCRT) with a pH of 6.3, a temperature of 20 °C, and an anaerobic selector hydraulic retention time (HRT) of 50 minutes, controlled nocardioforms to below detectable levels whereas nocardioforms were present in a completely mixed control. The full‐scale, anaerobic‐selector, activated‐sludge system performing EBPR at a 3.5‐day average MCRT, average temperature of 20 °C, and anaerobic selector HRT of 17 to 24 minutes reduced nocardioform organism levels below those achieved when the full‐scale plant was operated at conditions that did not permit EBPR (i.e., MCRT of 1.7 days and anaerobic selector HRT of less than 19 minutes). In the full‐scale plant, the lowest nocardioform organism levels and effluent dissolved orthophosphate concentrations were associated with the highest MCRT tested (4.6 days).