Using coagulation as a pretreatment to improve ultrafiltration processes for pulp mill wastewaters

The use of coagulation as a pretreatment alternative to improve the performance of membrane filtration process for pulp mill wastewaters was studied with a crossflow ultrafiltration membrane filtration apparatus. Various process and operating conditions affecting the coagulation and membrane filtration were examined, including coagulant type and dosage, pH, ionic strength, membrane material, crossflow velocity and transmembrane pressure. The results showed that coagulation could greatly reduce the flux decline and improve permeate water quality, whereas other the operating parameters have relatively minor effects. When compared to alum, ferric chloride was identified as a better coagulant for treating the pulp mill effluents. (author)