An investigation of reciprocating filtration system

Abstract

For combining certain advantages of dead-end filtration (low energy consumption), cross-flow filtration (sweeping of accumulated foulants) and backflushing (lifting of accumulated foulants), a reciprocating filtration system is presented in this study. In this system, a tubular ceramic membrane was used and driven by a piston and the forward–reverse filtration cycles were operated without cross-flow. At the beginning of each filtration cycle, the membrane was backflushed by filtrate in reverse direction by suction to reduce membrane fouling and then the filtration was in progress when backflushing was completed. After a few forward–reverse filtration cycles, the concentrated suspension of particles or solute near the membrane surface was discharged into a stock tank under the cross-flow condition. The polystyrene colloidal suspensions and the backwash wastewater were used as the feed streams and filtered. The ultrafiltration and microfiltration membranes with a range of pore sizes were also studied. In the experiment of maximizing the cumulative filtrate volume, it was found that the optimum time of a filtration cycle was 90 s, namely, forward and reverse was 87 and 3 s, respectively. The experiment was carried out using the particle size of 0.3 μm and a concentration of 50 ppm in polystyrene suspensions. There were filtered by the membrane with a pore size of 0.2 μm under the pressure drop of 50 lb/in. 2 (psi). The optimum discharge frequency for retentate was one for every three cycles. It was also found that the cumulative filtrate volume increased with an increase in both particle size and membrane pore size, but it decreased with an increase in feed concentration. Furthermore, an optimal cumulative filtrate volume was found on effecting the pressure drop. The process used in the study could be used to efficiently treat filter backwash wastewater from a water treatment plant.