The Study Of Membrane Pollution Of Microorganisms Isolated From Biofouling Layer Of PVDF Microfiltration Membrane

In this study,the membrane fouling caused by three dominant strains,Aeromonas caviae N25 and Aeromonas veronii M4 and Sphingobacterium caeni S3,isolated from PVDF microfiltration membrane were analyzed,which was important to reveal the basic mechanism of membrane biofouling.The main research resμlts were shown as follows:(1)The interaction and adsorption characteristics between three strains isolated from biofouling layer of MBR and PVDF microfiltration membrane were studied by thermodynamic method and interfacial adsorption theory.The resμlts showed that the surfaces of A.veronii M4,S.caeni S3 strain and PVDF membrane exhibited obviously hydrophobic properties,however,A.caviae N25 strain had a hydrophilic surface.The movement capacity of A.veronii M4 was higher than the others.In addition,the three bacteria and PVDF membrane were strongly charged and showed the typical electron donors.Among the various interfacial interaction energy components,the Lewis acid-base interactions of three bacterium-membrance systems occupied a dominant position.According to the XDLVO theory,the total interfacial interaction energy of three systems was negative,which indicated the adsorption potentials of three strains to the PVDF membrane.Among the three systems,the A.veronii M4-PVDF membrane combination had the lowest(negatively greater)value of interfacial interaction energy,which suggested that A.veronii M4 might be favored to the PVDF membrane.Moreover,the static adsorption results demonstrated that the adsorption quantity of A.veronii M4 to PVDF membrane was significantly higher than the others and the adsorption quantity of A.caviae N25 to PVDF membrane was the lowest one.With the increase of cell concentration,the adsorption capacity increased gradually.The adsorption process of three bacterium-membrane systems could be described by pseudo-second-order kinetics equation.(2)The filtration characteristics of the single-,dual-and triple-strains were studied.The results showed that the fouling potential of M4 was the highest,followed by S3 and N25 was the smallest.During mixed bacterial filter process,the pollution potential of dual-strains(M4 and S3)was the highest and the pollution potential of triple-strains was the smallest.The analysis of membrane pollution mechanism illustrated that the membrane fouling was mainly from the sedimentary layer during the dynamic filtration process,and the resistance radio from the sedimentary layer occupied the total resistance was over 80%.And the radio increased with the increase of the concentration of the bacteria suspension.The analysis of the filtration mechanism indicated that the filtration of single-bacterial suspension had a characteristic of significant filter cake filter during the dynamic filtration process.According to the XDLVO,the interaction between bacteria and bacteria from membrane surface was the main factor of causing membrane fouling during the late of filtration process.Among the 3 systems,N25 was inhibited to attach on membrane surface in N25-PVDF membrane system,while bacteria was promoted to adhere to membrane surface between M4-PVDF and S3-PVDF membrane systems.The analysis by FI-IR revealed that the peaks of PVDF membrane after filtered by the single-strains suspension were similar,and the characteristic peaks of PVDF membrane after filtered by the triple-strains suspension were different from those of single bacteria.(3)The growth curve,biofilm production as well as characteristic of biofilm attachment on PVDF membrane surface of N25,M4,S3 and their mixture were studied.The results showed that the growth period of S3 was the longest,and the growth period of N25 was the shortest,and the growth curve of the triple-strains was in the middle of the single bacteria.The biofilm biomass of the single-strain and triple-strains increased firstly and then decreased with the change of time.The biofilm biomass of triple-strains was the largest,and the biofilm biomass of N25 was the smallest.The ability of the single-strain as well as triple-strains attachment on PVDF membrane was different.The capacity of M4 and triple-strain attachment on PVDF membrane were stronger,but the capacity of N25 attachment on PVDF membrane was the weakest.Furtherly,it was found by fluorescence microscopy that M4 dominated in biofilm formed by the triple-strains,and the EPS from three strains as well as the intracellular substances from N25 and M4 had positive effect on biofilm formation,while the intracellular substances from S3 inhibited formation of biofilm.Water was filtrated by PVDF membrane which has been cultured with single-strain and triple-strains,which proved that triple-strains had the greatest biofouling potential.Among the single bacteria,the biofouling potential of M4 was the largest,followed by S3 and N25 was the smallest.