Research On Membrane Water Treatment Efficiency And Membrane Fouling Control Based On MTB Magnetotactic Characteristics

The membrane water treatment process has developed rapidly,which is widely used in the advanced treatment of drinking water and the reuse of sewage wastewater,and has a good interception effect on particles,microorganisms and viruses in the water,and the effluent quality is stable,but the membrane pollution problem during operation limits its large-scale development.Magnetotactic bacteria（MTB）are widely present in nature,and can synthesize nanomagnetic particles（magnetosomes）in cells,and under the action of magnetosomes,bacteria can feel the external magnetic field to produce magnetotropic behavior.Based on this behavior,MTB can migrate directionally along magnetic field lines to the solid surface for aggregation,and has a certain removal effect on heavy metals in the water body.In this study,MTB and ultrafiltration system were combined to explore the treatment efficiency of surface water and chromium（VI）and the control and optimization of membrane fouling by the composite process.The bacterial MTB-1 with magnetotactic properties was isolated from the muddy water mixture of Jiazi Lake of the University of Jinan,and the physiological and biochemical characteristics were analyzed in depth,and compared with the purchased magnetotactic bacterial strain MS-1.The results showed that the growth curves of the two strains had the same growth trend,and MTB-1 and MS-1 entered the logarithmic growth phase at about 4 h and 6 h,and entered the decay phase at 30 h and 28 h,respectively.The results of the two strains in the physiological and biochemical characteristics of urease,casein hydrolysis,starch hydrolysis,1%Na Cl growth,and hippuric acid hydrolysis were the same,and both showed negative results.There were certain differences between the two strains in the oxidase test,gelatin hydrolysis test and hydrogen peroxide test.The two strains were genetically sequenced and compared,and MTB-1 was compared with the isolated magnetotactic bacterium Stenotrophomonas sp.MTB-3 similarity was 97%,and MS-1 was more than 97%similarity to the Magnetospirillum magnetotacticum gene.The results showed that when the p H was 7.0,the dissolved oxygen concentration was 0.2mg/L and the bacterial dosage was 15mg/L,the removal effect of Cr⁶⁺was good,and the removal rate remained stable after rising to 19.2%with the extension of reaction time.The changes of membrane fouling during the operation of MTB-UF and N-UF systems were analyzed in depth,and the changes of transmembrane pressure difference（TMP）,membrane surface characteristics and microbial community structure were studied respectively.The test results show that coagulation pretreatment can slow down the membrane fouling rate during the ultrafiltration process of raw water in Jiazihu.After MTB was added,the membrane contamination trend of MTB-UF and N-UF was the same,and the TMP of MTB-UF was always higher than that of N-UF.After the magnetic field with an external strength of 33.71 m T,the TMP of MTB-UF showed a trend of first decreasing and then stabilizing and then rising,and after 10 min of the applied magnetic field,the pressure had a downward trend,and at the 90th minute,the TMP decreased by 5 KPa and stabilized for10 min,and the TMP increased again.It may be that under the action of magnetic field,the MTB on the membrane surface moves directionally,causing membrane surface contaminants and slowing down membrane contamination.The comparative analysis of SEM-EDS on the surface surface of the surface water ultrafiltration membrane of chromium（VI.）showed that the contact between bacteria and the membrane was accelerated after the addition of MTB,resulting in membrane pollution,so that the TMP of MTB-UF was higher than that of N-UF,the main pollutants on the membrane surface were organic pollution,and there were also inorganic pollution caused by some calcium ions,and after chemical cleaning,the pollutants could be effectively removed to make the morphology and morphology of the membrane surface similar to that of the new membrane;The contact angle detection results showed that after the addition of MTB,bacteria attached to the membrane surface,which reduced the hydrophilicity of the membrane and restored the hydrophobicity of the membrane after chemical cleaning.FTIR analysis showed that the N-UF membrane surface mainly existed in the form of phenols and alcohols,and the main pollutants on the MTB-UF membrane surface existed in the form of hydroxyl groups,hydrocarbons,phenols,alcohols,etc.From the perspective of changes in microbial community structure,comparing MTB-UF and N-UF microbial community structure,it can be seen that the species differences in the two systems are small,and the three largest phylums are Proteobacteria（Proteobacteria）,Firmicutes（Firmicutes）,Bacteroidota（Bacteroides）,because MTB belongs to the Proteobacteria phylum,after adding MTB,The relative abundance ratio of Proteobacteria bacteria in the ASB-MBR system was 85.17%,which was 30.21%higher than that of the N-UF system,while the relative abundance of Firmicutes decreased by 17.81%.This indicates that the microbial community structure was changed by the addition of MTB.