Application of immobilized psychrotrophs in ICCBR to treat domestic wastewater and its microbiological investigation

To guarantee the efficiency of biotreatment of domestic wastewater in chilly season, six high efficient cold-adapted microorganisms were isolated, and identified as Zoogloea, Aeromonas, Flarobacterium, Micrococcus, Bacillus, Pseudomonas. These cold-adapted microorganisms with 63.67% Chemical Oxygen Demand (COD) removal efficiency higher than that of mesophiles at low temperature were immobilized on soft polyurethane foams and applied to internal circulation compound bioreactor (ICCBR) to treat domestic wastewater. In an experiment period of 12 months, the treatment efficiency, ecological factors, sludge physicochemical properties, and microbiology were studied. Results showed that the average COD removal efficiency in the ICCBR was 85.79% between 4℃ and 10℃ in winter, and 86.66% in the whole year, and COD of systemic effluent was below 60 mg·L-1 which could achieve the first-degree B discharge standard of pollutants in China for municipal wastewater treatment plant. The reduction in microfauna and biomass on carriers could be associated with the seasonal temperature transients, the concentrations of protozoa and metazoan decreased from 110000±30000 microorgan-isms/mL sludge in summer to 35000±20000 microorganisms/mL sludge in winter, and biomass on car-riers increased in the beginning and slightly reduced in the end.