Effects of operating conditions on submerged hollow fibre membrane systems used as pre-treatment for seawater reverse osmosis

The potential of submerged hollow fibre membrane systems without the aid of coagulant was investigated as a pre-treatment for seawater reverse osmosis in this paper. The operation parameters such as filtration duration, backwash duration, backwash strength and the aid of air scouring during backwash were investigated in order to optimize the filtration performance and fouling control. The underlying fouling limitation mechanisms which result in those optimized operation parameters were also explored. It was found that periodical backwash with the permeate can provide effective removal of fouling layer and reduce the fouling rate during the filtration cycle. Results also indicated the strong inter-correlation among backwash strength and filtration duration and their effect on fouling rate. Excessive backwash strength was found unable to minimize fouling, and in fact, resulted in higher fouling rate during filtration. The percentage of removable fouling by backwash was also significantly affected by the inter-correlation between the backwash strength and backwash duration. By analyzing the composition of the feed, permeate and the solution after backwash, it was found that UF membrane (pore size 0.04 μm) can remove more than 60% of biopolymers. The biopolymers rejected by the UF membrane formed the cake on the membrane surface, and this fouling cake can be easily removed by periodical backwash.