Biofouling Characterization On The Microfiltration Membrane Interface And Its Influential Factors

Biofouling is an inevitable problem occurred to the membrane separation technology,and it has adverse effect on the separation efficiency and membrane service life.Due to the complexity of the biofouling process,there are still problems such as few studies of adsorption process of microorganisms on the membrane surface,the key factors affecting the development of biofouling still need to be clarified,and the chemical cleaning methods have insufficient understanding of bio-based pollution control mechanisms.In this paper,the PVDF membrane is taken for consideration.Firstly,the interfacial energy and adsorption curve of typical bacterial cells on the membrane surface are analyzed,and the key factors affecting the adhesion of bacterial particles on the membrane surface are identified.Second,the intrinsic correlation between long-term microfiltration membrane flux,resistance and biofouling was analyzed,and the influential factors affecting development rate of biological fouling was determined,and the change of interface energy in the development of biological fouling on bacteria.In addition,the long-term stability of the micro-filtration membrane is analyzed through investigation of the character of the micro-filtration membrane and the interfacial energy changes after the biological fouling and chemical cleaning.The sedimentation and adsorption behavior of bacterial particles at the interface of the microfiltration membrane was studied.By investigating the decrease of membrane flux and the change of fouling resistance caused by bacterial particle sedimentation,a model of bacterial particle sedimentation and fouling on the surface of microfiltration membrane was established.With the assistant of the XDLVO theory and the static adsorption experiments,the interface energy between the bacterial particles and the microfiltration membrane interface was calculated to determine the influence of different factors on bacterial adsorption.The results show that: in the early and stages of crossflow filtration,the biological fouling caused by bacterial particles fitted well with the filter cake plugging model,respectively,and the operating pressure and bacterial concentration were found to be the main influencing factors;The adsorption of bacteria was also affected and accelerated by the co-existence of protein and polysaccharides;for example,the membrane-bacterial interface energy of the microfiltration membrane after protein contamination has decreased from 11800 KT to-1953 KT.In addition,the environmental temperature,the ionic strength of water also proved to have a significant impact.The change of microfiltration membrane surface biomass and its effect on membrane filtration performance were studied.The growth law of biomass and the change of biological fouling resistance under different filtration conditions,as well as the resultant flux decline were analyzed..The interface energy between the membrane interface and the bacterial particles was calculated to analyze interception effect of the biofilm on the feed pollutants.The results show that the ambient temperature and the nutrient concentration of the feed liquid are the keys to determine the growth rate of the biofilm.And the final quality of the biofilm mainly depends on the feed property.There is a significant correlation between the quality of the biofilm attached to the membrane interface and the reversible fouling resistance of the microfiltration membrane,and the correlation with the irreversible fouling resistance is weaker.The presence of biofilm can effectively trap the feed components with strong biodegradability,but failed to trap degradable pollutant components.As the biofilm gradually matures,the interfacial energy between the bacterial particle and the membrane interface decreases significantly,indicating that the formation of the biofilm greatly is beneficial to the adsorption of bacteria onto the membrane surface,The interface energy drops to-8100 KT after 16 h of pollution,indicating that the adsorption capacity of bacteria continues to increase during the development of biological pollution.The character of the used microfiltration membrane were analyzed,and the effect of NaClO and NaOH cleaning on the flux and separation recovery of the microfiltration membrane was studied.The interaction between microfiltration membrane and P.aeruginosa particles was analyzed.The results show that long-term biological fouling will cause serious blockage of pores.Chemical cleaning can effectively remove the fouling layer,but there is a risk of destroying the membrane surface.After chemical cleaning,the interface energy between the membrane and bacteria is significantly reduced,resulting in the significant increase of the adsorption capacity of P.aeruginosa,the amount of bacteria adsorbed on the microfiltration membrane after washing with sodium hypochlorite reached about 200 times that of the initial PVDF membrane...