Effect of Fe-based micro-flocculation combined with gravity-driven membrane ultrafiltration on removal of aluminum species during water treatment

Abstract Aluminum (Al) as the third most element in the crust, with its exposure to increasing acid precipitation, has posed a risk in surface water contamination. In this work, a pilot-scale micro-flocculation/gravity-driven membrane (C-GDM) ultrafiltration process was performed without backwashing, flushing, or chemical cleaning of the membrane, to investigate the removal of aluminum species from feed water artificially polluted with Al. Two types of Fe-based coagulants were compared: FeCl3 and polyferric sulfate (PFS). The results revealed that the water flux stabilized during 60-day operation at 5.3 Lm-2h-1 with a low pressure of 70 mbar. Compared with FeCl3, the C-GDM ultrafiltration combined with PFS performed better for removal of total Al, reaching 75.0% removal. The average Al concentration in the produced effluent was less than 0.1 mgL-1, which is lower than world health organization (WHO) standard for drinking water quality (0.2 mgL-1). The average removal efficiencies of particulate Al and dissolved inorganically bound Al were the best at 94.9% and 92.6% respectively, while that of polymeric colloidal, strongly bound Al was the worst, being removed at only 32.9%. Additionally, the contribution of Al-species removal by the individual coagulation step was determined, and this was compared to stand-alone ultrafiltration and to the combined coagulation/ultrafiltration process. The findings of this work led to recommendations for practical application that C-GDM ultrafiltration process is a promising technology for Al removal, which can assist in the development of strategies to solve the problem of Al pollution for decentralized water supplies.