The overall objective of this project is to demonstrate the sustainable use of stable electrocatalytic anode materials to treat graywater for reuse in shower or laundry facilities. Specific objectives include: (1) verification of effective destruction of chemical oxygen demand (COD) and pathogens in graywater under both normal and shock loading conditions to meet Department of Defense (DoD) requirements for reuse; (2) assessment of disinfection byproduct (DBP) formation relative to new regulatory standards, (3) demonstration of treatment longevity; and (4) assessment of net energy requirements with respect to overall sustainability and costs. As part of objective (4), cathodically generated hydrogen will be captured, purified, and fed to a hydrogen fuel cell to limit overall energy demand of the treatment system.

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The approach for treating graywater for potable reuse consists of filtration (coarse through microfiltration) followed by electrochemical treatment using mixed metal oxide (MMO) electrodes. The initial filtration steps will consist of backwashing sand or screen filters. These filters will remove particulates and a large fraction of the COD without the need for energy intensive filtration processes such as ultrafiltration or reverse osmosis. Previous studies have shown that the COD of graywaters can be substantially reduced by moderate filtration. Reducing COD loading is important because it decreases the electrical energy demand required for electrooxidation, thereby allowing focused use of MMO anodes for treating the residual COD fraction. The electrochemical step will remove the remaining COD (to applicable standards) and provide disinfection without accumulation of DBPs above regulatory limits. Commercially available electrochemical cells and MMO anodes will be employed. Use of a divided electrochemical cell is planned, as this configuration will likely have several advantages, including improved removal of recalcitrant organic compounds and a decrease in the net generation of DBPs. A low energy electrodialysis polishing step to remove total dissolved solids will be employed, if needed.

To limit net energy demand, cathodically generated hydrogen will be collected and purified for use in a hydrogen fuel cell. This approach will limit net energy usage by taking advantage of the fortuitous reduction and hydrolysis reaction occurring at the cathode. Commercially available hydrogen purifiers (consisting of multiple sorbents) and commercially available hydrogen fuel cells will be used for this process step.

The graywater treatment technology to be demonstrated is readily deployable, sustainable (potentially powered via solar energy), does not require storage or use of hazardous chemicals, is able to treat a wide range of organic contaminants, provides disinfection, and does not produce significant quantities of disinfection byproducts. These qualities make the electrolytic treatment ideally suited to address the DoD’s need for graywater reuse. (Anticipated Project Completion - 2019)