| Aerobic granular sludge has many advantages such as compact layered structure,strong impact load resistance and saving project land.However,the stability problem of aerobic granular sludge has not been solved yet.The low temperature environment has a significant impact on the physical and chemical properties of aerobic granular sludge and the efficiency of pollutant treatment,which directly leads to difficulties in starting and operating sewage facilities under low temperature conditions.At present,most of the research on aerobic granular sludge adopts single temperature conditions,and there are few researches on variable temperature operating conditions.This subject aims to study the formation characteristics of aerobic granular sludge,pollutant treatment efficiency,EPS content,c-di-GMP content and the dynamic changes of microbial community composition during constant temperature and variable temperature operation.And analyze the impact mechanism of c-di-GMP on the startup and operation of lowtemperature aerobic granular sludge system.The formation characteristics of aerobic granular sludge under low temperature and in the process of variable temperature were investigated by starting two reactors at 10℃and 25℃ respectively at constant temperature,and then running the reactor at 10℃→25℃,25℃→10℃ after the aerobic granular sludge matured.The results showed that the rate of formation of particles in the system started at low temperature was slower than that at normal temperature.On the 60 th day,the particle sizes were 453.12 μm and 526.49μm,respectively.The aerobic granular sludge system started at low temperature shows good pollutant removal efficiency in the operation process.When the temperature changes,the sludge concentration and settling performance of the aerobic granular sludge will show a downward trend.The changes of EPS and c-di-GMP in aerobic granular sludge were investigated under the condition of low temperature and in the process of variable temperature.The results show that c-di-GMP has a regulatory effect on EPS content,and the aerobic granular sludge system increases EPS secretion to resist external stress caused by temperature changes.When the operating temperature decreased from 25℃ to 10℃,When the operating temperature decreases from 25°C to 10°C,the c-di-GMP concentration of the system started at room temperature and the system started at low temperature increased from 280.57 and 128.74 μg/g MLVSS to 308.02 and 216.93 μg/g MLVSS,respectively.Correspondingly,the EPS concentration increased from 147.27 and130.72 mg/g MLVSS to 283.69 and 157.40 mg/g MLVSS,respectively.When the operating temperature increases from 10°C to 25°C,the c-di-GMP concentration of the system started at low temperature increases from 190.54 μg/g MLVSS to 400.93 μg/g MLVSS,and the concentration of EPS increased from 142.78 mg/g MLVSS to 183.62mg/g MLVSS.Using high-throughput sequencing technology to investigate the relationship between aerobic granular sludge c-di-GMP,EPS and microbial community composition under low temperature and in the process of variable temperature.The results show that the decrease in temperature caused some EPS bacteria that are not suitable for low temperature to be eliminated from the system.During the start-up and temperature change,the relative abundance of c-di-GMP regulated bacteria in the system started at room temperature reached 5.67% and 2.43%,respectively.The total relative abundance of cdi-GMP regulated bacteria in the system initiated at low temperature reached 15.95%,10.22%,and 16.95%,respectively.Flavobacterium,Microbacterium,and Pseudoxanthomonas are c-di-GMP regulated bacteria that can be retained stably at room temperature and low temperature.The genus of regulating bacteria plays a leading role in regulating the extracellular polymer of aerobic granular sludge. |
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