Fouling mechanism of PVDF ultrafiltration membrane for secondary effluent treatment from paper mills.

• The application of PVDF UF membrane in pilot secondary effluent treatment from paper mills was studied. • Pore blockage and cake deposition were found to be the major fouling mechanism. • PVA-217 was identified as the main cause of the membrane pore blockage. • Ca2+ formed complexes with PVA-217 was developed as an efficient way to reduce membrane fouling. Papermaking industry discharges a huge amount of effluent and recycling of processed water with membrane technology has become predominate treatment protocol. In this study, poly(vinylidene fluoride) (PVDF) ultrafiltration membrane was employed to treat the effluent of secondary sedimentation tank from a paper mill. The results of 600 -hs continuous running showed that the PVDF membrane was seriously fouled with increased surface roughness during the filtrating process. Characterization of the fouled PVDF membrane revealed that pore blockage and cake deposition were the main fouling mechanism. The foulants in the pores were mainly oxygen-contained organics, and the foulants on the surface were mainly metal complexes and large particle. Wastewater analysis indicated the co-existence of PVA (1.0 mg/L) and Ca2+ (16.7 mg/L) in the secondary effluent. Pores blocking mechanism was caused by strong adheresion of PVA-217 and cake deposition mechanism was induced with macromolecular complexes of calcium ions bonding to PVA-217. The results obtained in this study demonstrated the fouling mechanism in the secondary effluent treatment. The understanding could help to find a feasible chemical method to clean the fouled polymeric membrane with washing agents as NaClO, NaOH and HCl in steps. [ABSTRACT FROM AUTHOR]