Research On Formation Of Granular Sludge And Its Efficiency Of Nitrogen And Phosphorous Removal

The problem of surface water pollution is increasingly serious in China recently; therefore the Chinese government published"12th Five-year-plan Scheme"which focuses on the nitrogen and phosphorus removal. How to meet this qualification economically and effectively had become the key issue. Granular sludge with denitrifying and phosphorus removal function was cultured in an Anerobic/Oxic/Anoxic-SBR. To investigate the formation and the biological nitrogen and phosphorus efficiency of granular sludge, sludge characteristics, biological activity as well as microbial community succession was studied. Via orthogonal experiment, optimal operation of SBR reactor was achieved.Granular sludge was cultured by synthetic wastewater. During the formation period, sludge concentration, sludge gravity, particle size, settling velocity as well as sludge activity increased continuously, and sludge moisture content decreased. In the meantime, the treatment efficiency of A/O/A-SBR system improved gradually. When treated with domestic wastewater, after a short period of adaption, the treatment requirements of the"12th Five-year-plan Scheme"could be achieved,the remove efficiency of nitrogen and phosphorus were 96.7 % and 79.9%.At the first stage of granular sludge formation, brown flocculent sludge had loose structure and low activity,phosphorus release during anoxic phase was obvious. During the second formation stage, self-condensation of the sludge became more obviously, tiny granule began to appear and grew bigger. The nitrification ability of the sludge increased in the same time. In the third stage, filamentous microorganism propagated largely, particle size increase to over 1mm; sludge was yellow, in regular shape and tight. The denitrifying phosphorus removal effect was better, the removal efficiency of COD,TN and PO43--P was 79.85%,95.34%,99.93%. During the formation period, dynamic changes could be observed in microbial species structure. Some of the partial dominant bacteria such as uncultured beta proteobacteria always existed, while others would disappear and replaced by new strains.Temperature is the most important factor that affects the treatment efficiency due to the results of orthogonal experiment. When wastewater with low temperature was treated by A/O/A process, prolong treatment time of each phase could improve the effect. Carbon source and COD concentration of influent are less important factors. When COD concentration was low or there are complex organics in the influent, adding some simple organic and prolong the treatment time of anaerobic phase would improve the removal of nitrogen and phosphorus. pH is not very important for COD and nitrogen removal while it will greatly affect the phosphorus treatment. pH 7-8 is optimal for the system. When pH of the influent is low, prolong the treatment time of oxic phase and increase aeration volume could improve the treatment efficiency of the system.