Experimental study of the dead-end ultrafiltration process using silicone dioxide suspensions

Applications of ultrafiltration (UF) membranes in water treatment have rapidly increased during the past decade. Successful operation of dead end UF processes requires rigorous experimentation and modeling in order to optimize the operating procedure. Optimum scheduling of forward and backwash cycles can play an important role in minimizing reversible fouling effects and controlling irreversible fouling. The objective of this work was to study the effect of varying the filtration and backwash periods on the operation of a pilot scale plant with a single 8 inch industrial dead end UF membrane. In this paper the results of the initial experimental work are shown for SiO2 (Aerosil 200) suspensions with concentrations of 500 to 4000 ppm. The results indicated that at low concentrations of SiO2 (below 500 ppm) no flux decline was observed for the duration of the experiments. At a higher concentration of 2000 ppm, flux decline started to appear after a few cycles of filtration which initially showed no flux decline. At 4000 ppm flux decline was observed from the first cycle. Moreover, the filtration period had a significant effect in this case. Using a filtration period of 4 min resulted in a complete blockage of the membrane before the cycle ended. With 3 min filtration period a consistent and continuous operation with about 80% flux decline was achieved. A long term operation was possible to do in the laboratory by completely recycling the backwash to the feed tank and carefully selecting the filtration and backwash pressures after doing some trial runs and measuring the actual flow rates. Using a concentration of 4000 ppm, a filtration to backwash period of 3:1 min. and backwash to filtration pressure of 36:16 psig (a ratio of 2.251) it was possible to operate continuously with a flux decline of about 80%.