Solar and Waste Heat Desalination by Membrane Distillation

This project comes under our effort to develop affordable technologies for sustainable rural development, particularly in regions where availability of drinking water is a problem. The quality standards required for healthy living in the case of drinking water, or for reliability in the case of industrial process water, necessitate improved technologies for the treatment of the water before use, as well as before discharge. Membrane distillation is a relatively new process for treating water and is potentially advantageous to existing water purification technologies (e.g. reverse osmosis). The potential benefits include: more cost effective as it has a low operating and maintenance as well as capital costs, utilizes low-grade heat; and not significantly affected by the feed water contaminants (ex. salt, Arsenic, Fluorine etc.).

In this study the desalination performance and operation and maintenance procedures of an air-gap type membrane distillation system are being developed using low-grade solar thermal energy (between 13 and 85 degrees Celsius) applied to a salt-water solution.

Feed water of a known salt concentration is pumped into a warm water collecting tank. The water in the tank is heated by a solar collector. A circulation pump runs the warm water through the membrane module. A cold water circuit is built up in a similar pattern as the warm water circuit, but with an air-to-water heat exchanger inserted to maintain a fixed cold water temperature. Our proposed method was evaluated based on product water flow rate, distillate quality, and assessment of salt concentration before and after passing through a Scarab membrane distillation module based system. The current portable system production capacity is about 30 L/hr of distilled water.