Membrane regeneration and filtration modeling in treating oily wastewaters

Traditional membrane cleaning methods generate waste cleaning waters; whose disposal costs are an increasing concern. The use of backflushed coalescing microfiltration for the pre-treatment of oily wastewaters prior to ultrafiltration is an interesting technique offering potential as a physical pre-treatment method. The concept of this technique is to pre-treat oily wastewaters with a large pore microfiltration membrane operated with backflushing where the oils are partly coalesced in the pores of the membrane. The permeate from this membrane can then be treated by ultrafiltration. The coalescing membrane must eventually be regenerated in order to maintain a desirable permeate flux. The present work investigates environmentally friendly physical membrane cleaning methods, such as backflushing with hot water or steam followed by pressurized air. The treatment of oily wastewater containing half seawater using a microfiltration (MF)/ultrafiltration (UF) hybrid system was studied in this work. The beneficial effects for steam cleaning were quite evident. The results were also modeled using four traditional fouling models and a combined filtration model. They indicate that fouling of microfiltration membranes is due to the presence of oil and grease and seawater colloids in membrane pores. Optimal cycle times between physical cleanings were found to be in the range of 1.6–2.2 h.