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 YT, 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 (F/M) 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.