Study On Simultaneous Nitrogen And Phosphorus Removal By Aerobic Granular Sludge Process In Treating Low Strength Domestic Sewage

Municipal wastewater treatment plants often encounter the problem of insufficientcarbon source, leading to poor removal performance of nitrogen and phosphorus. In viewof this situation, this paper focuses on the three parts of work: the cultivation of adequateaerobic granular sludge; operation process optimization of aerobic granular sludge forsimultaneous nitrogen and phosphorus removal; aerobic granular sludge-algae symbioticsystem for phosphorus and nitrogen removal.The first part is the cultivation of aerobic granular sludge. In the condition of reactorwith Ratio of height to diameter of2and low concentration influent with CODconcentration of200mg/L, aerobic granules could be cultivated successfully. Matureaerobic granules with yellow appearance, had perfect setting performance, whose SVI wasstable between20ml/g~40ml/g. The average particle size of aerobic granules cultivatedwith high strength and low strength influent were1.02mm and0.79mm.Maintaining shortsettlement time, reducing influent COD concentration and extending operation cycle time,decreasing the organic load rate and the growth rate of floc sludge,could be conducive toimproving granulation rate and ensuring the successful cultivation.The second part is operation process optimization of aerobic granular sludge forsimultaneous nitrogen and phosphorus removal. Aerobic granular sludge had very goodperformance in degrading organic matter and oxidizing ammonia. The stronger is theaeration and the longer is the cycle time, are the lower the effluent COD, ammonia andnitrite. Sludge age and anoxic time had little effect on COD, ammonia nitrogen removalperformance. Nitrate was mainly removed by denitrification, suppressed by carbon sourceshortage; a certain anoxic time could be beneficial to the removal of nitrate. TP wasremoved mainly at the aerobic stage. The stronger is the aeration and the longer is thecycle, the lower the effluent TP. A certain degree of sludge removal and anoxic time werebeneficial to phosphorus removal. For low concentration influent with COD of200mg/L, aeration intensity of0.2m~3/h, cycle time6h, sludge age40d, anaerobic time0.5h are theappropriate operation parameters for simultaneous nitrogen and phosphorus removal.Addition of the iron salt could promote phosphorus removal rate increased by9%.Observed productivity of aerobic granular sludge was far less than the conventionalactivated sludge process.The third part presents aerobic granular sludge-algae symbiotic system forphosphorus and nitrogen removal. The presence of algae changed the physical andchemical properties of aerobic granular sludge. The sludge color changed from yellow togreen, broken floc and irregular particles increased and settling properties declined, SVIincreased from31.4ml/g to54.0ml/g. Algae covering the surface of aerobic granularsludge increased the mass transfer resistance, which was not conducive to the degradationof organic matter and denitrification, having little effect on phosphorus removal however.Algae-provengting performance could play through the sludge replacement, changing thedistribution ratio of the influent ingredient and reduced lighting. Reduced lighting hadfastest algae-proof effect but could lead to particle disintegration; followed by sludgereplacement. Changing the ingredient of the influent had the slowest and worst weakalgae-killing performance.