Looking into reusing or reducing the reject brine from reverse osmosis, mainly in rural India as well as a few urban centers, for our client, Piramal Water Private Limited, our team brainstormed to come up with a number of creative as well as technical solutions. Each solution we came up with was evaluated based on practical considerations (scalability, viability, short-term feasibility, suitability), economic considerations (cost effectiveness, added economic value) and social considerations (community value and cultural sensitivity).
Under a business as usual scenario, the RO system is run at approximately 40% and the brine is discarded to either evaporate or recharge into the water table. This solution would not add any economic or social value and would contribute to environmental degradation.
The reject brine could potentially be used for laundry purposes by piping it to a communal laundry facility in rural areas or used in a commercial laundromat in urban settings. This would depend on the contents of the brine and the effect it would have on clothes. This is a solution we propose to pilot test.
Another idea looks at using the reject brine in a public restroom facility. It would add immense social value, especially in rural areas, but various social and cultural norms would have to be studied as well as the contents of the brine to understand the feasibility of this solution as well as the laundry idea.
A potential revenue generating solution that we came up with is using the brine for Aquaponics, which is essentially combining the technology of aquaculture (raising fish in tanks) with hydroponics (cultivating produce in water). Initial investment costs might be a hurdle for this solution.
Bioaccumulation is a potential solution to clean the reject brine. Certain plants that can bio-accumulate pollutants can be grown in the brine and the cleaned water can be re-used for other purposes or even re-run through the RO again. A major hurdle for this is to find plants that would accumulate salt. We are looking at the feasibility of pilot testing this idea.
Our most promising idea is evaporation of the brine to harvest salt. Incorporating water reclamation into the evaporation system would enable using the reclaimed water to cut the additional brine for re-run. This is another solution we intend to pilot test.
The brine could also be used for beautification/ landscaping, to develop a small garden/ park in the village or outside the franchisee outlet. This would involve investment by the franchisees, for which they might not be willing.
A solution to treat the RO brine is by infiltration to a treatment wetland, including native plants where possible. The brine would get treated as it percolates back to the ground water table. This would improve groundwater quality compared to business as usual but involves capital costs to set up, for which the willingness of the client would be needed.
The technical solution our team is looking at is further treatment through Capacitive Deionization. It is a process the removes salts and minerals from water by applying an electric field between two porous electrodes. It has been utilized along with biologically activated carbon to further treat RO brine with up to 90% reductions in total dissolved solids concentrations. Again the capital costs associated do not make this a feasible solution for our client.
Testing the brine for its contents, understanding the social and cultural norms of the locals which would lead to acceptance of any pilots and willingness of the franchisees to invest in the solutions are some of the issues we will be looking to further research in July/ August, 2011 when our team visits franchisees of Piramal Water Private Limited in Gujarat and Rajasthan.