Removing Trace Organics by Reverse Osmosis Using Cellulose Acetate and Polyamide Membranes

Abstract

A full‐scale (8‐cfs [0.22‐m³/s]) reverse osmosis (RO) water treatment plant equipped with conventional cellulose acetate membranes, and two pilot RO plants, equipped with polyamide membranes, were tested for their ability to remove total organic carbon and a broad range of trace organics, including volatiles, purgeables, neutrals, bases, phenols, and acids from lime‐clarified secondary municipal wastewater. The full‐scale RO system removed total organic carbon (TOC) by 89 percent to 0.95 mg/L at 84‐percent water recovery, and the pilot RO systems removed TOC by 99 percent to 0.1 mg/L at water recoveries of 52 and 67 percent, respectively. The two membranes tested showed significant differences in their ability to reject trace organics. All membranes rejected branched, complex molecules but varied in their rejection characteristics for smaller molecules, such as chlorinated solvents. The latter group was rejected to a varying degree by polyamide membranes but passed through cellulose acetate membranes. The use of RO for trace organics removal is evaluated by comparing cumulative removals of different treatment schemes with and without RO treatment.