PAC-PDMDAAC pretreatment of typical natural organic matter mixtures: Ultrafiltration membrane fouling control and mechanisms.

Precoagulation by polyaluminum chloride-poly dimethyl diallyl ammonium chloride (PAC-PDMDAAC) prior to ultrafiltration (UF) was conducted to evaluate the influence of PAC-PDMDAAC on controlling membrane fouling from typical natural organic matter (NOM) mixtures of humic acid (HA), bovine serum albumin (BSA) and sodium alginate (SA). Membrane flux decline and flux recovery after backwashing were investigated to evaluate the membrane fouling. The fouling mechanisms were determined from the floc size, floc structure and membrane resistance. PAC-PDMDAAC effectively alleviated membrane fouling caused by the HA, HA-BSA, HA-SA and HA-BSA-SA mixtures; furthermore, membrane fouling was better mitigated in the HA-SA and HA-BSA-SA mixtures. The untreated HA-SA and HA-BSA-SA mixtures caused much more serious total membrane resistance and fouling due to blocking and adsorption in the membrane pores by particles with sizes similar to those of the pores. The increased membrane flux and decreased irreversible resistance after the PAC-PDMDAAC pretreatment were attributed to the formation of flocs with a large size and small fractal dimension, which mainly formed a cake layer on the membrane surface. However, PAC-PDMDAAC was not particularly effective in reducing the irreversible membrane fouling originating from the HA and HA-BSA mixtures due to the formation of aggregates and pore blocking by microflocs.