Approaches to membrane fouling control in anaerobic membrane bioreactors

Various fouling control methods were investigated for polymeric and ceramic microfiltration membranes in the anaerobic membrane bioreactors where inorganic precipitates and/or fine colloids have been recently known as the most significant foulants: (i) Substantial improvement of flux was achieved by backfeeding of acidic wastewater through the membrane module. The backfeeding mode formed an acidic environment around the membrane pores and thus suppressed struvite formation. (ii) Struvite precipitation was also mitigated when an additional combined dialysis/zeolite unit was attached to the bioreactor. With this combined unit the flux improvement for the ceramic membrane, where struvite had a severer fouling effect, was achieved more significantly than that for the polymeric membrane. (iii) To control the deposition of organics and fine colloids onto the polymeric membrane, powdered activated carbon (PAC) was added into the bioreactor, which gave rise to the reduction of specific cake resistances of biosolids through the sorption and/or coagulation of dissolved and colloidal matter. (iv) The hydrophilic modification of polypropylene (PP) membranes by graft polymerization reduced membrane fouling. Its effectiveness was most substantial at 70% of the degree of grafting, indicating that there was an optimal degree of grafting. This is possibly due to the steric hindrance of grafted polymer chains and the increase in the hydrophilicity of the grafted PP membrane.