Waste Water

Dirty Bath Water Could Fuel Industry
By Charles Arthur, Technology Editor

A hot bath can do more than inspire deep thought, according to a British scientist who has used one to power a television set. Mike Rowe, of Cardiff University, has built a system that can generate 100 watts using the temperature difference between his cold water supply and a bath full of used hot water. Professor Rowe says his system can be applied on an industrial scale to provide large amounts of electricity at low cost. "This is part of a seven-year contract from the Japanese government, seeking ways to recover waste heat that presently goes down the drain - literally - from industry," Professor Rowe said yesterday. "All that this system needs to work is a temperature difference: a hot bath is about 55C, and the cold water supply about 50 degrees cooler. From that, we can generate 100 watts in our lab setup - and a colour TV needs only 80 watts."

The system uses a series of thermocouples, which produce power because the difference in temperature between two points will generate a voltage difference if the correct materials are chosen and placed at the respective points. Typical thermocouples use metals, but Professor Rowe has found that usable voltages are can also be generated by semiconductors such as germanium and silicon. The industrial applications are potentially huge, and could save millions of pounds by using hot water discharged from the steel, glass, ceramics and electricity generating industries. The steel industry, in particular, produces waste water with a temperature of 90C - too low to power a steam turbine, which requires 140C - so the water is often simply thrown away.

Water is an ideal material for thermocouple systems because it can absorb large amounts of energy. "The great thing is that in essence the energy source - the hot water - is effectively free. We have devised a system that can generate 2 watts foronly $5 [£3.12]." Professor Rowe's system could also benefit the environment if it is taken up by industries that currently discharge waste into rivers: high outflow temperatures have been blamed for affecting the life cycles of river animals and fish.