Study On Membrane Fouling Alleviation In Membrane Bioreactor By Modified Fe₃O₄ Carbon-coated Materials

Membrane bioreactor?MBR?is an emerging wastewater treatment process that combines traditional activated sludge treatment technology with membrane filtration technology.Due to the more stringent discharge standards and the increasing environmental protection awareness,the MBR process has showing the unique advantages of good effluent quality,high activated sludge concentration,low residual sludge production,high resistance to shock loading and small footprint.However,membrane fouling remains the biggest obstacle to the widespread use of MBR processes.Many studies in recent years have shown that membrane fouling can be effectively mitigated by adding various organic/inorganic flocculants to MBR.However,the flocculant will gradually fail in continuous operation,requiring long-term replenishment and thus resulting in an increase in operating costs.At the same time,the presence of the flocculant has an adverse effect on the microbial activity,leading to a decrease in the removal rate of the contaminant.Fe₃O₄ particles?MP?have high specific surface area and are easy to be separated from water.In recent years,MP have been widely used in the field of water treatment as adsorbents.It has been pointed out that MP,as a conductor material,can enhance the effect of electron transfer and improve the activity of microorganisms,to enhance the utilization of SMP and other dissolved organic matter by microorganisms and reduce the membrane fouling of MBR system.In this study,biodegradable carbon sources?cellulose and starch?and Fe₃O₄particles were combined to prepare Fe₃O₄ carbon-coated materials and modified with amino groups.Based on the enhanced microbial activity of Fe₃O₄ particles,biological flocculation was further enhanced.Fe₃O₄ particles were added to improve the degradation efficiency of SMP by microorganisms and promote the aggregation of sludge flocs,so as to realize the inhibition of membrane fouling in MBR.The properties of modified Fe₃O₄ carbon-coated materials were characterized by SEM-EDS,XRD,FTIR,Zeta potential analysis and N₂ adsorption-desorption.The results showed that the biodegradable carbon source is successfully coated in Fe₃O₄ particles,and the materials has a high specific surface area and a high-density surface positive charge.In the MBR continuity experiment,it was found that the membrane fouling rate of MBR reactor with modified Fe₃O₄ carbon-coated material was significantly reduced.Fe₃O₄ amino starch particles had the best effect in alleviating membrane fouling,and its average operating cycle was twice as long as that of the blank control group.The inclusion of biodegradable carbon source did not affect the improvement of microbial activity by Fe₃O₄ particles.Compared with the blank group,the activity of microbial dehydrogenase in the modified Fe₃O₄ carbon-coated materials increased by more than40%,which was conducive to the reduction of SMP and EPS concentration in the sludge mixture?SMP decreased by more than 15%,EPS decreased by more than 11%?.The inclusion of biodegradable carbon source is of great significance to promote the aggregation of sludge flocs.The addition of Fe₃O₄ amino starch granules significantly promoted the sludge flocculation effect.The sludge flocculation particle size in the reactor increased by more than 54%compared with the blank group,which greatly reduced the possibility of membrane pore blockage and further slowed down the membrane fouling.Based on high-throughput sequencing,the bacterial community structure study showed that Flavobacterium sp was enriched in the reactor with Fe₃O₄starch-coated granules.As EPS producing bacteria,Flavobacterium sp increased the EPS content in the sludge,increased the hydrophobicity and agglomeration effect of the sludge,and then improved the particle size of the sludge.