Final Report: Innovative Water Desalination System for Small CommunitiesEPA Contract Number: EPD17038
Title: Innovative Water Desalination System for Small Communities
Investigators: Srinivas, Girish
Small Business: TDA Research Inc.
EPA Contact: Manager, SBIR Program
Project Period: September 1, 2017 through February 28, 2018
Project Amount: $100,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2017) RFA Text | Recipients Lists
Research Category: Small Business Innovation Research (SBIR) , SBIR - Water
In many parts of the country groundwater withdrawals exceed recharge rates and this has caused groundwater-level declines, reductions to the volume of groundwater in storage, lower streamflow and lake levels and land subsidence. It is expected that the demand for groundwater will continue to increase because of population growth, especially in the arid West. Further, surface-water resources are fully appropriated in many parts of the country, creating additional groundwater demand. Development of brackish groundwater and seawater as an alternative water sources can help address concerns about the future availability of water and contribute to the water security of the Nation. Thus, there is a need for a technology that produces high yields of clean water that: 1) can desalinate brackish water (which is actually plentiful throughout the US) and seawater, 2) has a low operating cost, 3) is reliable and durable, and 4) that is scalable for producing from 100,000 to 1,000,000 gallons per day of potable to meet the needs of small communities (<10,000 population). TDA proposed to develop the components for an energy-efficient, scalable water desalination system.
To remove salt, TDA developed thermally regenerable sorbents. The key discovery is that certain ion exchange (IX) materials can be regenerated with hot water, rather than chemically. The advantages of thermally regenerable sorbents are: 1) they do not require high pressures (like reverse osmosis (RO)), 2) no additional chemicals are needed for regeneration (unlike conventional IX), and 3) they require much less energy than distillation because the sorbent removes soluble ions (the minor components), rather separating the major component (water). In this project we made new, more robust IX materials, specifically for thermal desalination and thereby develop a process that can potentially be less expensive than RO.
During this Phase I project, we have successfully developed a thermally regenerated water purification process. In this project we synthesized new IX resins and compared their performance to commercial resins. We found that the commercial resins had much greater salt capacity than the ones that we made. We tested two combinations of commercial IX resins and found that while they removed salt well at ambient temperature they degraded after only a few thermal cycles.
Since the commercial IX resins were not stable, we decided to try a different family of sorbent materials. Over the years, we have developed a variety of sorbents with different functional groups. We can make these materials in a manner that gives them either acid groups or basic groups. We found that these sorbents are very robust and we could cycle them without capacity loss.
In order to evaluate the usefulness and economics of our process, we developed a 100,000 gal/d desalination system operating with a 600 ppm brackish water feed and estimated the production cost per 1000 gallons of potable water. From this analysis we determined our system could produce water at roughly the same production cost as RO systems. With further improvements in the IX sorbent salt capacity, we could be much less expensive than RO. Since our new IX sorbents are far from fully optimized, we expect to be able to at least double or even triple their salt capacity.
Based on our system analysis, we find that the best commercial application for our process is desalinating brackish water with salt concentrations below 2000 ppm. At higher concentrations, the capital costs for sorbent based process (whether it be our IX sorbents or commercial IX resins) become too high to compete with RO. Fortunately, the US has vast amounts of brackish water that could use our technology.
In summary, we have successfully developed IX sorbents that are low-cost, thermally stable and can economically desalinate brackish water. With further optimization of the IX sorbents that we have developed, we expect to be able to develop a lower cost, scalable alternative to RO.