Prof. Rajnish Kumar, Department of Chemical Engineering, IIT-Madras
For decades, scientists have known that gas hydrates — ice-like crystals formed when water traps certain gases under low temperatures and moderate pressure — could, in principle, purify contaminated water.
The idea was always attractive: Water locks itself into crystals while salts and other impurities are left behind. But there was a catch.
Separating the crystals from the remaining wastewater proved cumbersome and energy-intensive, preventing the technology from competing with membrane-based systems, such as reverse osmosis (RO).
Researchers at the Indian Institute of Technology, Madras, now say they have overcome that bottleneck.
The team has developed and patented a gas hydrate-based process that forms hydrate crystals directly in the gaseous phase, eliminating the need for filtration or centrifugation to separate them from wastewater.
In tests using actual petrochemical effluent supplied by GAIL (India) Ltd, the system recovered more than 65 per cent of the water, removed 84-93 per cent of contaminants, and recycled over 99 per cent of the hydrate-forming gases used in the process.
Developed by Dr Subhash Kumar Sharma under the supervision of Prof Rajnish Kumar, the process offers an alternative to RO. (RO’s membranes are prone to fouling, require periodic replacement and generate solid waste. Thermal processes avoid membranes but consume significantly more energy.)
A mixture of propane and HFC-134a is introduced into the contaminated wastewater under carefully controlled temperature and pressure. Water molecules assemble around the gas molecules, forming solid hydrate crystals while salts, ammonia, suspended solids and organic contaminants remain in the liquid.
The crystals are then gently melted to recover purified water, while the gases are captured and reused in the next cycle.
The technology consumed 3.88 kWh of electricity for every cubic metre of water recovered — comparable to seawater reverse osmosis and substantially below thermal desalination methods. The researchers estimate a levellised water cost of about 14 paise a litre and report a carbon footprint 35–70 per cent lower than that of conventional membrane- and heat-based technologies. The treated water met the Central Pollution Control Board standards for industrial reuse.
Kumar said the process could help industries reduce freshwater consumption while meeting increasingly stringent zero liquid discharge requirements.
The technology is at readiness level 6, indicating it has moved beyond laboratory proof-of-concept. The team plans pilot-scale demonstrations using wastewater from the pharmaceutical, textile and fertilizer industries.
Published on July 13, 2026
