The Change Patterns Of Extracellular Polymeric Substances In Aerobic Granular Sludge System During The Temperature Change

Compared with traditional activated sludge,aerobic granular sludge has better sedimentation performance,higher biomass concentration and smaller footprint.In northern China,wastewater treatment plants are usually built in summer and start in winter in order to save time.Whereas,in high latitude areas,winter is long and water temperatures usually vary between 8-10?which is far below the optimal temperature range of microorganisms,thus making it difficult to meet the national effluent standards.So far,main focuses concerning aerobic granular sludge is its cultivation under single temperature condition,while little attention is paid to the effect of temperature change.In this study,seasonal water temperature change was simulated during the operation of aerobic granular sludge reactor,the rule of extracellular polymer substance?EPS?changing was explored and effect of EPS was investigated based on the analysis of microbial community structure.In this study,after obtaining low-temperature and normal-temperature aerobic granular sludge,low-temperature reactor was gradually warmed while normal-temperature reactor cooled.Aerobic granular sludge with simultaneous nitrification and denitrification function was formed in 20 and 25 days respectively at normal temperature and low temperature.After the formation of granules,the growth rate of particle size at low temperature was higher.Both systems showed excellent removal efficiency on COD,NH₄⁺-N and TN.NO₂^--N and NO₃^--N were accumulated to a variable extent.Temperature change made aerobic granular sludge system break down temporarily,granules disintegrated,but then gradually recovered to normal particle size.During particle formation process,EPS concentration first decreased but then increased until reached a steady state.Temperature has a great influence on EPS.During the cooling process,EPS concentration decreased from 37.95 mg/g VSS to20.45 mg/g VSS,while during the heating process,EPS concentration increased from26.30 mg/g VSS to 51.32 mg/g VSS.For mature aerobic granular sludge,increasing temperature will stimulate more secretion of EPS.The concentration of TB-EPS is much higher than LB-EPS,which plays a key role in the formation of aerobic granular sludge.During the operation,microbial community structure in two reactors had undergone great changes.For mature aerobic granular sludge systems,the warming process enriched the community structure and improved?-diversity.Microbacterium,Tsukamurella,Zoogloea and Flavobacterium are cold-adapted bacteria,which can live in normal and low temperature while maintain high abundance.Saprospiraceae,Candidatusc Nitrotoga and paracoccus are exclusive functional genus in low-temperature reactor and the key bacterial group in aerobic granular sludge system.