Recovery And Stabilty Of Aerobic Granular Sludge Under Low Carbon And Nitrogen Ratio

Aerobic granular sludge is used to treat high ammonia nitrogen,toxic organic wastewater with its good settling performance,high biomass,microbial diversity,impact resistance and so on.However,in the pilot wastewater treatment processes,too low COD/N often need to suplement carbon source,which increase process costs grestly.In the aerobic granular sludge system,the low COD/N affects settling performance,nitrification performance and microbial community structure of aerobic granular sludge could be affected by low COD/N.which often leads to the disintegration of aerobic granular sludge.In this paper,aerobic granular sludge stored at 4 ? for 30 days was investigated to explore the activity recovery under low COD/N conditions.Then settling ability,nitrification performance and microbial population structure of the aerobic granules were tested to figure out the effects of carbon and nitrogen load increase and COD/N in reduction.The results were shown as follows:(1)Aerobic granular sludge which was stored at 4 ? for 30 days was revived after 25 days.COD removal efficiency of A and B reactors was both 95%and ammonia nitrogen removal efficiency was 90%,respectively.During the recovery period,SVI30 of the system increased and then decreased,with the A and B reactors's SVI30 increased from 101 ml/g and 83 ml/g to 125 ml/g and 118 ml/g,and then decreased to 80 ml/g and 57 ml/g.respectively.(2)After the recovery,carbon and nitrogen load was increased and COD/N ratio was decreased to 2.However,there seemed little effect on the physical properties of the aerobic granular sludge.Settling ability was well maintained,and the SVI30 of A and B reactors were always kept at 60 ml/g and 75 ml/g.and MLSS was 5 g/L and 3.7 g/L,respectively.COD removal efficiency was declined,but still maintained at more than 70%,ammonia nitrogen removal rate were fluctuated,which may increased compromise system stability.(3)Increasing carbon and nitrogen load and decreasing COD/N ratio will increase the richness of the microbial community of aerobic granular sludge,but will decrease the diversity.The dominant species were Thauera.which was accounted for more than 44%of the total bacteria.Nitrosomonas from was increased 1.01%to 7.15%.(4)The enhancement of the carbon and nitrogen load and reduction of COD/N.w ill reduce EPS secretion of the aerobic granular sludge.The EPS of aerobic granular sludge was negatively correlated with SVI30.The EPS of aerobic granular sludge increased first and then decreased.which was beneficial to maintain the activity of aerobic granular sludge and ensure the removal efficiency of nitrogen.(5)Under different COD/N conditions,the cycle performance of the aerobic granules were basically same.Approximately 8%of the influent nitrogen is used for its growth and reproduction of microorganisms.About 19.2%of the nitrogen is removed by simultaneous nitrification and denitrification in the aerobic stage.