About 39% of all the fresh water withdrawn from rivers, lakes, and reservoirs in the United States is used for cooling electric power plants. Most of that water ends up in clouds of vapor.
Engineers at MIT have now developed technology which captures fresh water from power plant cooling towers.
The project began as part of an attempt to improve the efficiency of fog-harvesting systems that are used in many water-scarce coastal regions as a source of potable water. Those systems, which generally consist of some kind of plastic or metal mesh hung vertically in the path of fogbanks that regularly roll in from the sea, are extremely inefficient, capturing only about 1 to 3% of the water droplets that pass through them.
The reason for the poor efficiency is that as a stream of air passes an obstacle, such as the wires in these mesh fog-catching screens, the airflow naturally deviates around the obstacle. These deviating airstreams carry droplets that were heading toward the wire off to the side.
The researchers found that if the incoming fog gets zapped first with an ion beam, not only do all of the droplets that are in the path of the wires land on them but even droplets that were aiming for the holes in the mesh get pulled toward the wires.
The stream of water vapor from a power plant’s cooling tower is much more concentrated than any naturally occurring fog, and that makes the system even more efficient. The water captured is pure, even if the cooling water is salty or contaminated.
A typical 600MW power plant could capture 380 million litres of water a year.