On March 21, 2014, the Securing Water for Food Grand Challenge for Development and the United States Bureau of Reclamation announced the launch of the Desal Prize. The second call for proposals under Securing Water for Food, the Desal Prize aims to incentivize the creation of an environmentally sustainable small-scale brackish water desalination system that can provide potable water for humans, as well as water appropriate for crops in developing countries.
The winning innovation will be selected based on its fulfillment of several criteria, including:
The Desal Prize is the second "call" under the Securing Water for Food Grand Challenge for Development. While water desalination technologies currently exist, few are suitable for use in rural or remote settings-that's why the United States Agency for International Development (USAID), the Swedish International Development Cooperation Agency (Sida) and the Ministry of Foreign Affairs of the Kingdom of The Netherlands (MFA-NL) launched the Desal Prize. The Desal Prize also benefits from a partnership with the U.S. Bureau of Reclamation who are providing the Brackish Groundwater National Desalination Research Facility as well as technical guidance. There are currently six teams, including CIDS, competing in the semi-finals.
A team from CIDS, including Malynda Cappelle, Tom Davis, and Shane Walker, (link to Expertise pages) will operate a high recovery process called ZDD in the Desal Prize competition. This process, known as Zero Discharge Desalination (ZDD), has been evaluated at the Brackish Groundwater National Desalination Research Facility (BGNDRF), as well as in California and Colorado, and has shown the potential for 95-98% recovery. There are multiple suppliers for all of the systems and all equipment is expected to be available commercially. The estimated recovery of the prototype is 93%.
The renewable energy system will include photovoltaic panels, inverters, batteries for load stabilization, and associated electrical panels. The EDM system will be powered entirely by DC. The remaining systems will require AC power.
Brackish groundwater (from BGNDRF Well #3) will be fed to the two-stage nanofiltration system (NF). This will produce drinking water that is expected to meet WHO drinking water and the irrigation water quality requirements. The NF will have two types of membranes installed and minimal pre-treatment needs:
The NF concentrate will be fed to an electrodialysis metathesis system (EDM)where 60-65% of the ions will be removed. The treated stream from the EDM, called diluate, will be fed back to the NF for additional water recovery. The only chemical feed for the EDM is salt (NaCl). Cations in the NF concentrate will combine with the Cl from NaCl to form highly soluble chloride salts in a highly concentrated waste stream called Mixed Cl. Anions in the NF concentrate will combine with Na from the NaCl to form highly soluble sodium salts in a highly concentrated waste stream called Mixed Na. These waste streams can be combined to produce a solid waste stream that is non-hazardous and a liquid stream. This solid will contain mostly calcium and magnesium salts and can be used to improve irrigation water quality by improving the sodium absorption ratio (SAR). Lower SAR values will improve irrigation water infiltration into the soil, improve crop yields.
Because silica is not removed by the EDM, it will tend to concentrate in the proposed hybrid system. A small silica purge stream will be used to maintain the silica at a level that will not precipitate in the NF or EDM systems. The combined waste stream, containing 7% of the initial brackish water volume, will be disposed of in a small evaporation tank.