Physical cleaning efficacy of hollow fiber nanofiltration membranes in drinking water applications

摘要

The aim of this research was to study the role of hydrodynamic conditions on the efficacy of physical cleaning (rinsing and backwash steps using water and/or air) for hollow fiber nanofiltration (HFNF). Bench-scale inside/out HFNF membranes, as well as hollow fiber ultrafiltration (HFUF) tested as a reference, were fouled in dead-end (DE) or crossflow (CF) operation with synthetic water consisting of a mixture of sodium alginate and kaolin clay. Six physical cleaning strategies (3 average water velocities ranging from 0.06 to 0.27 m/s x 2 air velocities (0.51 m/s or none) were tested after triplicate filtration cycles. The physical cleaning efficacy was assessed by performing a mass balance recovery of the alginate and kaolin fed in the system. No difference in physical cleaning efficacy was observed for the two types of membranes in CF operation. High water velocity and air addition improved the physical cleaning efficacy. During CF operation, alginate and kaolin were mostly (75%-86%) recovered in the concentrate as opposed to physical cleaning waters (below 8%). Fouling management achieved by a combination of physical cleaning and CF operation was superior to what was achieved in DE operation with physical cleaning. For HFNF, the energy costs for physical cleaning were marginal compared with those associated with CF operation, but can be reduced by using a shorter backwash duration and air-assisted forward flush.