Low-temperature distillation technology licensed to Sterling Water

The low-temperature distillation method of desalination developed by the New Mexico State University (NMSU) in the USA has been licensed to Sterling Water LLC of Qatar.

The system uses the natural effects of gravity and atmospheric pressure to create a vacuum in which water can evaporate and condense at lower temperatures than normal for distillation.

A successful proof-of-concept model was developed last year and the NMSU-led project transferred the science and prototype model from lab bench to a market capable product. Sterling Water and the NMSU company Arrowhead Center Inc concluded license agreement negotiations during February 2010. Sterling Water intends to bring the commercial model into full manufacturing in the coming year.

The research team, led by Dr Nirmala Khandan in the College of Engineering at NMSU, built an inaugural unit which produced over 200 gallons per day (750 L/d) or enough pure water for about 15 people.

Two 10 m vertical tubes, rising respectively from a tank of saline water and a tank of pure water, are connected by a horizontal tube. The barometric pressure of the water columns creates a vacuum in the headspace.

At ambient temperatures, evaporation from the pure-water side will travel to the saline side and condense as the system seeks equilibrium. Raising the temperature of the water in the headspace over the saline column slightly more than that of the freshwater column causes the flow to go in the other direction, so that pure, distilled water collects on one side and the brine concentrate is left behind in a separate container.

Kevin Boberg, Arrowhead Center CEO, traces the origins of the technology to a process, first developed by researchers in Florida, that makes distillation of saline water possible at the relatively low temperatures of 45-50ºC rather than the 60-100ºC required by most distillation processes.

The 30-foot-tall NMSU prototype is powered by a solar panel. Khandan and his research assistant, civil engineering doctoral student Veera Gnaneswar Gude, have modified the process to incorporate a thermal energy storage device that allows the system to operate around-the-clock, using stored energy at night. The Institute of Energy and Environment housed in the NMSU College of Engineering helped to instrument the system.

Two problems to be addressed in the commercial version are the height of the water columns and brine disposal.