Evaluation of reverse osmosis and nanofiltration for in situ persulfate remediated groundwater

Sodium persulfate is a common oxidant used for in situ chemical oxidation (ISCO) remediation of ground water contaminants (e.g., trichloroethylene (TCE)). Following ISCO unused persulfate and oxidation by-products such as sulfates remain within the groundwater at elevated levels. In this laboratory study the performance of three membranes: one nanofiltration (NF) membrane (designated DK) and two reverse osmosis (RO) membranes (designated AE and AG), manufactured by GE Osmonics, Inc., were evaluated for the removal of total dissolved solids (TDS), mainly persulfate and sulfates, and other associated by-products from a simulated groundwater. Experiments consisted of short-term sheet membrane evaluations, long-term spiral wound membrane evaluations and membrane compatibility tests. The general order of membrane performance was AE >AG>DK. SEM analysis of membrane surfaces clearly showed that both the DK and AG membranes experienced degradation and cracking after exposure to elevated sodium persulfate solutions for 30 days while the AE membrane appeared unchanged. This finding is in agreement with the membrane performance test results, again confirming that the AE membrane was the best membrane of this group.