Onsite wastewater treatment and potable reuse technologies represent significant electrical energy consumption and operational costs at DoD fixed installations. Low electrical energy processes, such as those in the osmotic membrane bioreactor - membrane distillation (OMBR-MD) system, accomplish high quality wastewater reuse objectives and represent an opportunity for energy independence and water supply security. Currently, fixed installations recycle gray water (to a limited extent) for non-potable reuse applications; however, the DoD is considering technologies that recycle both gray and black water for potable reuse.
The objectives of this project are to scale-up and demonstrate the OMBR-MD system (developed through SERDP project ER-2237) for wastewater treatment and high-quality reuse applications while utilizing waste-heat energy and meeting target performance water quality and energy metrics at demonstration scale during long-term operation.
The competing technology for decentralized wastewater treatment and reuse is a conventional membrane bioreactor (MBR) followed by reverse osmosis (RO), which is an electrically energy intensive process that also generates a brine waste stream. Through engineered osmosis and distillation processes and use of waste heat existing on-site at DoD installations, the OMBR-MD system produces potable-quality product water with minimal electrical energy input and minimal waste, resulting in lower operational costs as well as water and energy savings.
An innovative OMBR system that applies forward osmosis (FO) membranes will be utilized. In this OMBR applications, water is extracted across the semi-permeable FO membrane from a low salinity solution in the bioreactor into a high salinity draw solution (DS). In the OMBR system, wastewater is fed into a bioreactor and the FO membrane provides high rejection of contaminants in the wastewater. As water is extracted across the FO membrane into the DS, the DS becomes diluted. The diluted DS is sent to a reconcentration process (e.g., membrane distillation (MD)) that reconcentrates the DS and generates high-quality product water. Compared to the microfiltration or ultrafiltration processes in a conventional MBR, the OMBR offers the advantages of much higher contaminant rejection (semi-permeable membrane in FO versus microporous membrane in conventional MBRs) with less fouling (lower hydraulic pressure).
As directed by Executive Order 13834, DoD facilities must reduce potable water consumption. Wastewater recycling for potable reuse can help address this requirement. Novel technologies, such as OMBR-MD, that utilize waste heat may have lower energy consumption compared to the conventional approaches to wastewater recycling. When waste heat is available, the optimal specific energy required by OMBR-MD is less than 50% of the competing technology.
Waste heat existing on-site at DoD fixed installations amounts to 138.6 trillion BTU/yr (40.6 billion kWh/yr). With this amount of waste heat, OMBR-MD could, in principle, produce 125 MGD of potable water, which is 53% of potable water consumption at fixed DoD sites in FY 2016. (Anticipated Project Completion - 2024).
Glover, C.J., J.A. Phillips, E.A. Marchand, and S.R. Hiibel. 2022. Modeling and Life Cycle Assessment of a Membrane Bioreactor–Membrane Distillation Wastewater Treatment System for Potable Reuse. Separations, 9(6):151. doi.org/10.3390/separations9060151.