Effect of addition of Rhodobacter sp to activated-sludge reactors treating piggery wastewater

Under aerobic conditions. the decay rates of purple nonsulfur bacteria (Rhodobacter sp.) in the light and dark follow first-order kinetics with rate constants of 0.22 and 0.32 day(-1), respectively. The performance of the conventional activated-sludge reactor (CASR) treating anaerobically pretreated piggery wastewater (656 1,110 mg chemical oxygen demand, COD/L) can be enhanced by the addition of Rhodobacter sp. By performing regressive and statistical analyses using the proposed model and experimental data. the kinetic constants k and Y-T, and the fraction of refractory organic materials (f) of the Rhodobacter sp-supplemented activated-sludge reactor (RASR) are 40% larger, 21% less. and 34% less than those of the CASR, respectively. From parametric sensitivity analyses, the substrate removal efficiencies of the CASR and RASR are most sensitive to the parameters k and the food to microorganisms ratio (FIM) but least sensitive to the parameter f: the specific oxygen utilization rates of the CASR and RASR are most sensitive to the parameters a and k but least sensitive to the parameter b. (C) 2001 Elsevier Science Ltd, All rights reserved.