Direct Contact Membrane Distillation (DCMD) for Industrial Wastewater Reuse: Managing the Accumulation of Organic Compounds in DCMD Product Water

Treating complex, highly saline industrial wastewaters, such as produced water from oil and gas extraction, is very costly, but direct contact membrane distillation (DCMD) is a novel process that can decrease water treatment costs. In DCMD, a heated feed stream is distilled at low–temperature (40-80°C) inside a membrane module and the distillate is collected in the permeate collection stream.  While many researchers have shown that DCMD systems have high salt rejection, few studies have analyzed the rejection of organic compounds (OCs), which are present in many industrial wastewaters. The research outlined in this presentation indicates that due to the temperature gradient between the feed and permeate collection streams, volatile and semi-volatile compounds can accumulate in the permeate collection stream at higher concentrations than in the feed. As a result, the OC concentration in DCMD product water should be carefully monitored especially for applications with human exposure. To evaluate the accumulation of OCs in the DCMD product water, flux tests of synthetic wastewater (brine solutions containing industrially relevant OCs of varying volatility) were tested in a batch DCMD system. The water flux and concentration of OCs in the feed and permeate collection reservoirs were monitored over 5 hours.  A Fickian mass transfer model was developed to fit the data and describe the change in reservoir concentration over time. This model can be used to predict whether the DCMD product water will meet the OC discharge requirements and determine if post-treatment is necessary.