Intermittent crossflushing of hollow fiber ultrafiltration systems

The successful operation of dead-end ultrafiltration systems depends on the effectiveness of cleaning (hydraulic and/or chemical cleaning). In this study, backwashing conditions such as pressure and duration were studied in order to maximize the net flux per cycle. Monitoring the backwash flux and turbidity of the backwash water showed that the efficiency of backwashing was more dependent on backwashing time than pressure. The effectiveness of backwashing was significantly improved by the use of crossflushing. In general, 99.9+/-1% flux restoration could be achieved when backwashing was preceded by crossflushing while 94.5+/-1% could be achieved by backwashing alone. Crossflushing was more effective when the crossflush velocity in the fiber was in the turbulent regime (v congruent to 1.6 m/s). Crossflushing and pressure pulsing can be employed to increase the efficiency of dead-end, hollow fiber ultrafiltration systems because the frequency of backwashing and chemical cleaning, permeate consumption and system down time are reduced.