AWWA WQTC65800

Treatment and disposal of concentrate from nanofiltration (NF) and reverse osmosis (RO) membrane filtration processes is an important issue facing utilities in areas of scarce water supply. Feasible disposal options for membrane concentrate are ultimately site specific and depend on the concentrate's quantity and quality. It has been proposed that removal of trace pollutants such as arsenic from membrane concentrate may increase the number of disposal options or even allow for concentrate reuse. This paper presents results of an on-going study exploring chemical treatment of membrane concentrate, with emphasis on coagulation using iron chloride followed by solid-liquid separation. Simplified concentrate solutions at ionic strengths representative of NF/RO concentrate (0.2 and 0.7 M) were prepared in the lab using specific ratios of major ions (e.g. sodium, bicarbonate, etc.). Removal of arsenic from these simulated concentrates was determined experimentally using small volume jar test procedures. Solids formed during treatment were separated from solution using 0.2 micron pore size filters. Removal of arsenic as functions of background matrix, natural organic matter (NOM) source, and coagulant dose are presented. Includes 3 references, tables, figures.