Effect Of COD And Nitrogn Loading On The Stability Of Aerobic Granular Sludge In Treating Wastewater Of Low COD/N Ratio

Compared with floc sludge,aerobic granular sludge has better performance.However there are few theoretical studies on the stability of aerobic granular sludge under different COD and NH₄⁺-N loading.This topic studied the stability of aerobic granular sludge under different COD and NH₄⁺-N loading under the condition of low COD/N ratio.This experiment inoculated aerobic granular sludge stored for 6 months under COD/N:200/40,and constantly improved COD and NH₄⁺-N loading to1000/250,at the same time addi ng external loop operation.Sludge physicochemical characteristics,pollutants treatment performance,and further analys is of sludge microbial community were investigated in the process of dynamic change.The findings will provide theoretical and practical b asis for the stable operation of aerobic granular sludge in wastewater with different COD and NH₄⁺-N loading.The detailed results showed that:（1）Under low COD and NH₄⁺-N loading（i.e.200/40-400/80）,R1 and R2operated stably.The SVI₃₀ of the two reactors was basically maintained at 68 m L/g and 77m L/g,SVI₅/SVI₃₀ was basically maintained at about 1,COD and NH₄⁺-N removal rates were about 95%and 99%,respectively.When COD and NH₄⁺-N loading was 400/100,due to the physical structure f ragility of granular sludge and obvious denitrification effect,the physical characteristics of the two reactors changed greatly,but eventually stabilized gradually.When COD and NH₄⁺-N loading was further increased to 600/150,because of stopping its external circulation operation,the R1 eventually caus ed the system breakdown.R2 reactor operated stably and remained stable after further increase of COD and NH₄⁺-N loading.（2）In the process of COD and NH₄⁺-N loading from low to high,the PS in the loose layer of granular sludge always exist ed,but the PN did not,which indicated that the PS in the outer layer of granular sludge was important to maintain the stability of the outer layer of granul ar structure.However,in the tight layer of granular sludge,the content of PN gradually exceeded that of PS,and the hydrophobicity gradually increased,indicating the high internal environmental adaptability of the system particles.At the same time,in the process of organic component change of EPS,excessive component change indicate d the environmental deterioration of the system.The long-term existence of tryptophan protein-like substances and aromatic proteins indicated their importance to the stabili ty of granular sludge.（3）Increasing COD and NH₄⁺-N loading of the system led to relative fluctuations in the richness and diversity of the microbial community.The external circulation operation was conducive to improving the richness and diversity of th e microbial community and increasing the number of microbial population,so as to optimize the community structure and improve the performance of collaborative treatment of pollutants.