| Both aerobic granular sludge and membrane bioreactor are sewage treatment technolog which can reduce the equipment area and improve the quality of the effluent.Our previous studies succeeded in cultivating aerobic granular sludge(AGS)directly in an internal-circulation membrane bioreactor.On this basis,the aerobic granular sludgemembrane bioreactor(AGS-MBR)which has been in stable operation for 383 days has was studied in this experiment.This experiment mainly discusses whether stimulating the growth of filamentous bacteria can promote the increase of particle size of granular sludge in membrane bioreactor and its mechanism.The AGS-MBR was fed with synthetic wastewater,which had a COD:N:P ratio to be 100:5:1.This experiment was divided into two periods,one time for the first 28 days,and the operation mode of the reactor at this stage was exactly the same as that before.The second period was 28-56 days.During this period,continuous aeration of sludge in the reactor at 28 days stimulated the growth of filamentous bacteria,followed by normal operation according to the phase?.During the whole experiment,the changes of dissolved oxygen,temperature and transmembrane pressure of membrane components in the reactor were recorded in real time,and the effluent water quality was analyzed every day.The extracellular polymeric substance of sludge was detected regularly,and the changes of sludge were observed by optical microscope and electron microscope,the changes of sludge particle size were detected by laser particle size meter,and the microbial community succession was observed by high-throughput sequencing.The AGS-MBR will be in a stable state after long-term stable operation.At this time,the reactor has good treatment effect for various pollutants,and the sludge morphology is regular,but the overall particle size is small(the average particle size is about 200 m).After continuous aeration of sludge in the reactor,filamentous bacteria obtained growth advantages and grew in large quantities.The most filamentous bacteria in the reactor was norank_p_Saccharibacteria,and they were in absolute dominant species(accounting for over 50%)during the phase?.After stimulating the growth of filamentous bacteria,the particle size of granular sludge also increased,and the particle size of sludge in the reactor increased rapidly from 200 ?m to nearly 400 ?m.The ratio of protein and polysaccharide and the extracellular polymeric substance conten of granular sludge was higher than that of flocculent sludge,which may be an important reason for sludge granulation.The treatment effect of organics in the AGS-MBR has been stable,with an average removal rate of 98.48%.However,the nitrogen and phosphorus removal ability of the reactor depends on the environment with alternation between aerobic and anaerobic,with the average removal rate of total nitrogen and total phosphorus being 93.7±4.6% and 90.1±5.8% respectively.Moreover,when the particle size of granular sludge increases,the nitrogen and phosphorus removal ability of the reactor will be more stable.In addition,this experiment also studied the recovery of the AGS-MBR after restart after being stopped for 20 days.The results show that compared with the initial start-up time of the reactor,the restarting time was significantly shorter.Moreover,the removal effect of pollutant was good and the granulation time of sludge was short.The results show that the AGS-MBR has good recovery performance and operation stability.Overall,this work proved that stimulating the growth of filamentous bacteria in AGS-MBR could effectively increase the particle size of sludge and enhance the ability of the reactor to deal with pollutants.In addition,the AGS-MBR has good recovery performance and operation stability. |
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