EXISTENCE OF CRITICAL RECOVERY AND IMPACTS OF OPERATIONAL MODE ON POTABLE WATER MICROFILTRATION

Results from a potable water microfiltration (MF) pilot study employin g untreated surface water are reported. The effects of filtrate flux a nd recovery on direct flow, outside-inside, hollow fiber MF fouling ra tes, and backwash effectiveness are presented. Constant flux experimen ts suggested the existence of a critical recovery below which MF fouli ng rates were low and effectiveness of backwashes was high and relativ ely independent of the recovery. However, in the range of experimental conditions investigated, fouling rates increased dramatically and bac kwash effectiveness decreased steeply when this critical recovery was exceeded regardless of the flux. In general, for a fixed recovery, spe cific flux profiles analyzed on the basis of volume filtered per unit membrane area were insensitive to filtrate flux. Fouling was accelerat ed by operating membranes at constant flux rather than at constant pre ssure, in part, because of membrane compaction and cake compression. C hanging the mode of filtration between constant Aux and constant press ure is shown to have no effect on MF filtrate water quality. For any g iven capacity, membrane area requirements are decreased, and power req uirements are increased when membranes are operated at constant flux r ather than at constant pressure.