Rejection of wastewater-derived micropollutants in high-pressure membrane applications leading to indirect potable reuse

The rejection of emerging organic micropollutants is an important issue where sources impaired by waste-water discharge are used to augment drinking water supplies. Because previous findings from bench- and laboratory-scale membrane experiments indicated that nanofiltration and to a lesser extent reverse osmosis (RO) membranes can incompletely reject organic micropollutants, this study investigated the efficiency of reverse osmosis membranes in rejecting these compounds at conditions simulating full-scale installations. Compounds investigated were classified by their physicochemical properties. Rejection of solutes was studied using a two-stage laboratory membrane skid and two full-scale RO trains. Full-scale studies did not reveal any quantifiable detects of any target compound, except for low concentrations of caffeine in permeate samples of the second and third stages of one facility. In general, hydrophilic ionic compounds were efficiently removed by steric and electrostatic exclusion. Although there was no evidence that hydrophobic solutes such as steroid hormones partition into permeates, the rejection of chloroform at one facility was rather poor, confirming findings from laboratory-scale experiments. Findings suggest that fouling layers present on membranes in full-scale installations result in an improved rejection of hydrophilic nonionic and especially hydrophobic solutes.