The effects of pretreatment on membrane distillation of cooling tower blowdown water

In the membrane processes, pretreatment of the hardness is an effective way to minimize membrane fouling, and to increase the quality of the permeate. Many pretreatment methods can be applied for hardness removal in way of individual or combined before membrane processes. In this study, effects of pretreatment, pH adjustment, caustic soda (NaOH) softening and soda ash (Na2CO3) + caustic soda softening, on desalination performance of the coal fired power plant cooling tower blowdown water (CTBD) by membrane distillation (MD) was investigated. By the MD system operated with hot feed (60°C) and cold permeate (20°C) sides of membrane, approximately 32 LMH permeate flux and more than 99.8% salt rejection were obtained in all experiments. While it was observed that the recovery rate of raw CTBD was 66.2%, recovery rate of pretreated CTBD with caustic soda was 79.4%. It was also found that pretreatment significantly reduces membrane scaling.