Modeling the Concentration of Volatile and Semivolatile Contaminants in Direct Contact Membrane Distillation (DCMD) Product Water

Direct contact membrane distillation (DCMD) is an emerging water treatment technology that has high salt rejection; however, its commercialization potential for applications such as seawater desalination or industrial wastewater reuse may be limited by low rejection of volatile and semivolatile contaminants. In this manuscript, a contaminant concentration (CC) model describing the transport of volatile and semivolatile contaminants for DCMD systems was developed and validated using data from the bench-scale DCMD treatment of synthetic wastewaters. The DCMD tests showed that the more volatile contaminants (methyl-tert-butyl ether, acetone, pentanone, butanol, and hexanol) accumulated in the permeate collection stream at greater concentrations than in the feed stream. The validated CC model (average normalized root mean squared error ≤11.3%) was then used to evaluate the product water quality from the large-scale DCMD treatment of oil and gas produced waters. The modeled product water contaminant concentrations exceeded the Environmental Protection Agency limits for discharging to publicly owned treatment works. This indicated that DCMD treatment of produced waters may require additional processing to meet discharge requirements.