Study On The Performance And Membrane Fouling In Aerobic Granular Sludge Membrane Bioreactor: Effect Of Superficial Superficial Air Velocity

Aerobic granular sludge membrane bioreactor（AGMBR）,a novel wastewater treatment process combining aerobic granular sludge and membrane bioreactor（MBR）,can not only combine the advantages of the two,such as high-quality effluent,simultaneous nitrogen and phosphorus removal,small footprint,etc.,but also solve the problems of both,such as serious membrane fouling,low efficiency of nitrogen and phosphorus removal of MBR and high suspended solids concentration in the aerobic granular sludge effluent.Here,the AGMBR process was used to treat municipal sewage.The aerobic granular sludge cultivated by our research group was used as the inoculation sludge,and the PLC was adopted to control the progress of the sequencing batch reactor（SBR）reactor.The aeration intensity in the SBR was controlled by a rotameter to adjust the to 1.6 cm/s,2.1cm/s and 2.6 cm/s,respectively.The effect of air flow rate on the operation efficiency and membrane fouling in AGMRB reactor was studied.The effluent of COD,ammonia nitrogen,TN,NO₃^–-N and NO₂^–-N were tested using the sewage detection method to investigate the sewage treatment efficiency.When the superficial superficial air velocities were 1.6 cm/s,2.1 cm/s and 2.6 cm/s,respectively,the COD removal rates were 95.16±1.41%,94.85±1.16%and 95.90±2.21%,respectively;the ammonia nitrogen removal rates were 99.45±0.27%,99.54±0.35%and 99.70±0.10%,respectivle;the removal rates of TN were 63.41±3.60%,62.90±2.68%and 60.59±2.90%,respectively.It can be seen that efficient treatment of sewage was achieved in AGMBR.At the same time,the change of trans-membrane pressure（TMP）was monitored by a vacuum pressure gauge.It was found that when TMP was equal to 10 k Pa and the air velocities were 1.6 cm/s,2.1 cm/s and 2.6 cm/s,respectively,the running time were 65,90 and 105 days,respectively,indicating that the increase of superficial superficial air velocity effectively mitigated the membrane fouling.When TMP was equal to 20 k Pa and the air velocities were 1.6 cm/s,2.1 cm/s and 2.6 cm/s,respectively,the running time of were 70,96 and 112 days,respectively.When TMP was equal to 30 k Pa and the air velocities were 1.6 cm/s,2.1 cm/s and 2.6 cm/s,respectively,the running time were 76,100 and 118 days,respectively.When TMP was equal to 40 k Pa and the air velocities were 1.6 cm/s,2.1 cm/s and 2.6 cm/s,respectively,the running time were 81,104 and122 days,respectively.It can be seen that at the later stage of the sharp rose of TMP,the increase of air velocities aggravated the membrane fouling,because TMP lasted 11,8,and 10 days,respectively,from 20 k Pa to 40 k Pa.Research on the filtration characteristics of the sludge mixture in the AGMBR reactor showed that the increase of superficial superficial air velocity promoted the production of tightly bound extracellular polymeric substances（TB-EPS）.Compared with TB-EPS,soluble microbial products（SMP）and loosely bound extracellular polymeric substances（LB-EPS）had a better correlation with membrane fouling.Protein（PN）was the main component of SMP,LB-EPS and TB-EPS,and played an important role in the formation and stabilization of aerobic granular sludge.In addition,the surface characteristics of the sludge mixture,such as the contact angle,zeta potential,and particle size,also determined its filtration characteristics.In the early stage of the sharp change of TMP（10 k Pa and 20 k Pa）,the increase of superficial superficial air velocity was conducive to the reduction of the hydrophobicity of the sludge mixture,the increase of the negative surface charge and the increase of the particle size,which played an important role in mitigating membrane fouling.In the late stage of the sharp rise of TMP（30 k Pa and 40 k Pa）,the increase of superficial superficial air velocity increased the hydrophobicity of the sludge mixture and reduced the negative surface charge,which intensified membrane fouling.Based on the analyses of high-throughput sequencing（HTS）,it was found that the change of superficial superficial air velocity caused major changes in the microbial community structure of the sludge mixture.Analysis of the fouled membrane morphology by scanning electron microscopy and atomic force microscope showed that with the increase of superficial superficial air velocity,the dense cake layer formed on the surface of the fouled membrane gradually became loose and porous.The results of membrane resistances and membrane blocking model fitting indicated that the main form of membrane resistance under this test condition was cake resistance.The membrane blocking model of three air velocities changeed from intermediate blocking model to cake blocking model,indicating that the formation of cake layer in the later stage of TMP increasing intensified membrane fouling.The analyses of foulants on the membrane surface revealed that the polysaccharide of SMP,LB-EPS and TB-EPS were the key factors causing membrane fouling.Under the same TMP conditions,the concentrations of SMP,LB-EPS and TB-EPS on the membrane surface were decreased with increasing air velocities,which maybe due to the formation of cake layers with air velocities of 2.1 and 2.6 cm/s were more loose and porous.Compared with the superficial air velocity of 1.6 cm/s,more SMP and EPS were easy to enter the membrane pores and caused the membrane pores blocking which is consistent with the result of membrane resistances.When TMP was equal to 10 k Pa,SMP was the main cause of membrane fouling.When TMP were equal to 40 k Pa,TB-EPS became an important factor affecting membrane fouling due to the formation of a cake layer on the membrane surface.In addition,the observation of three-dimensional excitation–emission matrix,energy dispersive X-ray spectroscopy,fourier transform infrared and confocal laser scanning microscopy suggested the main foulants on membrane surface were protein and polysaccharide.The HTS results showed that the microorganisms on the membrane surface retained the dominant bacteria in the sludge mixture.