Home-use Desalination

Household water treatment is on the rise globally, driven by a lack of reliable municipal supplies and a rise in education of water-borne illnesses. Reverse osmosis (RO) is a the dominant technology due to its high contaminant removal rates, simplicity, and affordability. These units are typically installed under sinks, mounted to walls, or placed on countertops; and many contain pre-treatment filters, one reverse osmosis membrane, and post-treatment modules. Water is pressurized to 40-80 psi and inputted into the semi-permeable membrane where contaminants are rejected and outputted as a brine stream separate from the purified stream. In many off-the-shelf units, the brine stream is 50-75% of the input water and with water scarcity rising globally, governments like India are starting to impose stricter standards. The GEAR Lab is striving to solve this water waste problem with two projects:

• installing and testing commercially-available RO systems in a brine reuse architecture in remote Navajo Nation households

• developing a home desalination system using electrodialysis with Eureka Forbes Limited based in India

Reverse Osmosis with Brine Reuse in the Navajo Nation

The GEAR Lab began working in the Navajo Nation as part of a grant sponsored by the U.S. Bureau of Reclamation. 30% of homes in Navajo Nation are not connected to a piped network. Instead, they must haul water for their homes and livestock from distributed wells containing slightly saline, or brackish, water. This water is not recommended for consumption so people must pay a high cost, in addition to time, gas, vehicle maintenance, etc., for bottled water. Commercially-available RO systems are capable of treating the brackish well water while also being affordable and easy to maintain. The high water wastage, however, limits adoption for communities like Navajo Nation who rely on water hauling. The quality of this "waste water", or brine, is slightly more saline that the input water, as it contains all the same contaminants but in a smaller volume. The team at GEAR Lab hypothesized that this brine stream could be diluted in the household cistern/storage tank for further use with negligible impact on household water tasks (washing, mopping, etc.). In April of 2025, nine homes were recruited for a yearlong study to test this hypothesis by installing commercial RO systems in convenient brine reuse architectures. Results and finding from this study will be used to form recommendations for remote home desalination systems in Navajo Nation and other like communities around the world.

Interested in installing a reverse osmosis system with brine reuse? Check out the handbook developed during the one-year field trip.

Household Electrodialysis System Development

Electrodialysis is an alternative desalination technology that uses an electrical potential applied across a stack of alternating anion and cation exchange membranes to form product and brine streams. Since this technology is capable of achieving higher recoveries than reverse osmosis (>80%), it could be better suited for household desalination in water-stressed areas. Functional requirements for a home-scale ED system were identified by interviewing stakeholders across India, including end users, distributors, and manufacturers. A model for brackish water ED desalination was developed by the GEAR Lab to facilitate design and analysis of different stack configurations and system architectures. Applying these models, the optimal geometry, flow-rates, and applied voltage for total cost minimization were explored using a genetic algorithm, for satisfying the production rate (9-15 L/hr) and product concentration (100-300 mg/L) requirements for the device.

The first two bench-scale prototype systems were developed in conjunction with our partner, Eureka-Forbes Limited, and experimentally demonstrated >80% recovery from feed concentrations as high as 3000 mg/L in a batched operation mode.

To further reduce costs, a novel single-pump architecture was developed. Typically, two pumps are used, one for the product stream and one for the brine stream. To recover more than half of the feedwater as product water, the brine is recirculated. In this new single-pump architecture, a flow restrictor on the brine stream reduces the flow rate to ensure more of the feedwater is recovered as product water. This architecture was successfully demonstrated in a benchtop setup with both synthetic and real brackish water.

Data taken during these trials was used to validate the GEAR Center’s ED model for this unique architecture. The validated model was then used to perform optimizations to determine a cost-effective, high-performing stack design. Due to rising component costs, in order to achieve a salinity decrease competitive with reverse osmosis (>90%), optimizations show an electrodialysis stack alone will cost the same or higher than an entire retail reverse osmosis system. The GEAR Lab is continuing to explore innovative ways to reduce the cost of electrodialysis systems while maximizing performance.

Sponsors

Eureka-Forbes Limited

Tata Center for Technology and Design

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