Membrane Anti-biofouling Modification And Investigation Of Its Properties In Membrane Bioreactor

Membrane bioreactors (MBRs) have been widely used in wastewater treatment. But a major obstacle for the application of MBRs is the rapid decline of the permeation flux as a result of membrane fouling. Thus, developing antifouling and low cost membrane material is necessary. It is essential for steady application of membrane and development of MBR.In this work, novel membrane materials, which were fabricated by modification the non-woven (NWF) with three hydropilicity materials, were developed according to the fouling characteristics in MBR.(1) Synthesis functional polyvinyl alcohol(PVA)/4-vinyl pyridine(4VP) copolymer using Ce(IV) as initiator. The appropriate reaction condition was:PVA concentration of 8 g/L,4VP concentration of 0.16 mol/L, Ce(IV) concentration of 4 mmol/L, reaction time of 240 min and reaction temperature of 60℃. Preparation of novel NWF composite membrane based on polyvinyl alcohol/4-vinyl pyridine copolymer was carried out by adsorption on polypropylene non-woven fabric (NWF) membrane surface and pore walls to improve both hydrophilic and antibacterial properties of the membrane. Experiment results demonstrated that surface properties, both physical and chemical characteristics of the modified membrane, were significantly altered. The results showed that the PVA-g-4VP modified membrane had hydrophilic and strong antifouling properties. Furthermore, antibacterial property of modified membranes were investigated by Live/Dead staining, which results indicated that there was less bacteria attachment on the PVA-g-4VP modified membranes, and the modified membranes surface was thus demonstrated to be very effective in preventing biofilm formation.(2) A novel NWF composite membrane was prepared by ozone pretreatment, chitosan coating and glutaraldehyde crosslink to resist the adsorption of proteins and the adhesion of bacteria. Experiment results demonstrated that the surface morphology and both physical and chemical characteristics of the composite membrane were significantly altered. The results showed that the composite membrane had hydrophilicity and higher protein rejection. Furthermore, antibacterial property of the composite membranes were investigated by staining, which results indicated that there was less bacteria attachment onto the composite membranes, and the composite membranes surface was thus demonstrated to be very effective in preventing biofilm formation, especially for the membrane with glutaraldehyde crosslink. In order to enhance the stability of composite membrane, preparation of porous composite membranes through chitosan crosslinking on/in the NWF outer and internal surface was carried out. The antifouling characteristics of the composite membranes in the submerged membrane bioreactor were investigated. The composite membranes showed better filtration behaviors in MBR than the original NWF membrane. The antifouling property of the modified membranes in the MBR was enhanced. The irreversible fouling resistance decreased.(3) Tailoring of NWF membranes surface properties via surface-initiated atom transfer radical polymerization with 2-hydroxyethyI methacrylate (HEMA) as monomer was carried out. The length and density of the grafted HEMA polymer chains, which form a uniform layer in the membrane pores, can be independently controlled. The length of grafted HEMA polymer chains can be regulated by changing the grafting temperature and grafting time. The density of grafted HEMA polymer chains can be regulated by adjusting the reaction time of ozone treatment on membrane surface. Both the length and density of grafted HEMA polymer chains were key factors for obtaining PHEMA-grafted membranes with desired antifouling properties, and the influence of the length of grafted PHEMA chains was more significant than that of the density. The results can provide valuable guidance for designing and fabricating antifouling membranes with grafted functional polymer.