Research On Polymeric Alumminum-Iron And Polymer Ferric Sulfate Enhanced Biological Phosphorus Removal In A~2 /O Process

In recent years, with the development of the economy of Yangtze River Delta region, more and more untreated sewage or incompletely untreated sewage that produced by industry, agriculture and residents directly discharged into Tai Lake, resulted in an extended nitrogen and phosphorus concentration in the water body. Serious eutrophication occurred frequently. A stricter local discharging standard was made to prevent the frequent outbreak of cyanobacteria in Tai Lake. Most of the wastewater treatment plants in Tai Lake region need to transform and optimize the processes in order to meet the new standards. Chemical enhanced biological phosphorus removal is one of the most widely used technologies in wastewater treatment plant upgrade. However, overdosage, poor sludge flocculation are the main problems when chemical enhanced phosphorus removal was applied. In this study, a lab scale model that simulated the operation condition of Lucun wastewater treatment plant in Wuxi was established. Through the automatic control dosing system biological phosphorus removal in the A~2/O process was improved. The effects of the chemicals on the functional microorganism in the A~2/O system were studied.In this experiment, polymeric aluminum-iron and polymer ferric sulfate were added at the end of aerobic tank in A~2/O system. The results showed that the two chemicals had little effect on COD, NH4+-N and TN removal in A~2/O system. These three items of the effluent could meet the the calss A standard in Municipal Sewage treatment plant Pollutant discharge Standard (GB18918-2002). TP removal could be improved by the chenmical addition. The TP concentration of the effluent was below 0.5mg/L when the dosage of polymeric aluminum-iron was 1.61mg/L (measurement of aluminum) or when that of polymer ferric sulfate was 2.99mg/L (measurement of ferrum). With the addition of the chemicals, sludge production and the size of the floc increased, the sludge settling ability was improved, and Zeta potential of the effluent decreased which indicated a good water quality of the effluent. The results showed that the gross of EPS varied little with chemical addition, however the ratio of albumen to polysaccharide decreased. When the dosage of the chemicals was increased, the concentration of TP and Fe3+ in the EPS increased slightly. The concentration of PHB increased as well. Therefore, it was concluded that the chemicals had little effect on nitrobacteria while would improve the performance of PAOs within the dosage in this research. The microbial diversity in the A~2/O system became less after the addition of the chemicals. Although the impact on TP removal and microbal performance were similar, polymeric aluminum-iron was more economic than polymer ferric sulfate.The analysis of the sludge taken from Wuxi Lucun and Chengbei wastewater treatment plant (WWTP) revealed that, it had little effect on nitrobacteria while had a great effect on PAOs when polymeric aluminum-iron had been added into the aerobic tank for a long time. The the concentrations of PHB in the sludge from the biological reaction tank of the two plants were lower. It showed that the sludge in the two plants had no biological phosphorus removal capacity. Phosphrous removal of the two WWTPs completely relied on chemical phosphorus removal. The flocculation capacity of the sludge decreased, Zeta potential of the effluent increased slightly therefore deteriorated the water quality of the effluent.