Development of an efficient approach for separating bubbles and flocs in a submerged membrane ultrafiltration process

This work was carried out to investigate the impact of air scouring and membrane configuration on ultrafiltration (UF) performance in a hybrid process of coagulation-UF. To eliminate the adverse impacts of air scouring, the concept of separating flocs in the submerged membrane module was proposed. The performance of three types of floc separation devices, including a cylinder module, a module without a floc separation device and a stacked inclined plate module, was compared. In the coagulation-UF process (i.e., without air scouring), the average transmembrane pressure (TMP) growth rates of the cylinder module, the module without a floc separation device and the inclined plate module were 0.58, 0.76 and 1.38 kPa/h, respectively, indicating lighter membrane fouling of the former two membrane configurations. In the coagulation-air scouring-UF process (with an air scouring rate of 35 mL/min), the stacked inclined plate module showed better effluent water quality (lower UV 254 ) and floc integrity (the floc size was about twice that of the other two configurations). Further, the optimization of the air scouring rate was conducted when the inclined plate module was used, and the optimal value was determined to be 60 mL/min for air rates ranging from 0 to 100 mL/min.