We first studied Diffusion Gap Distillation (DGD) under a Phase I/II DOE SBIR award (GRANT NO. DE-FG02-06ER84525) for a desalination process driven by our steam-generating solar collectors.  This early work showed the potential for DGD to compete with other thermally driven desalination technologies (e.g., MSF, MED).  However, our work concluded that the dominant technology for seawater and brackish water desalting--reverse osmosis (RO)--was not likely to be challenged by DGD.

    Our next phase of DGD development recognized fundamental limitations with RO: for inland brackish-water desalting plants, the cost for the disposal of the waste brine from the RO process imposes a severe penalized on the overall Cost-of-Water (COW). Our work under a Phase I/II USDA SBIR award (Award No. 2019-33610-30171) applied DGD to brine concentration with the ultimate goal of achieving Zero Liquid Discharge.

      A major challenge for our work under the USDA SBIR was to prove a stable design for a DGD processor that was a multi-plate assembly of large plastic heat exchangers.  The lessons learned in our USDA SBIR work provided the design guidance for scaling up the DGD technology for brine concentration, which was the target application for our entries in both the DOE Solar Desalination Prize and the USBR More Water, Less Concentrate competition.   Our submission to DOE as a semifinalist in the Design Phase of the Solar Desalination Prize describes a solar-driven facility that recovers approximately 95% of the waste brine from a brackish-water RO desalting plant as pure water at $1.29 per cubic meter (Levelized Cost of Water).  Our final report to the USBR under the More Water, Less Concentrate competition summarizes the one-week operation of the brine concentrator, shown in the figure at the left, that processed waste brine from RO at the Yuma Desalting Plant from brackish water.