Going to the toilet may be the answer to a cleaner environment, as a Hamilton engineering consultant sees his idea take form in America: drying sewage sludge to be used in place of coal.

At 89, Patrick Potter from Patrick Potter and Associates, a consulting engineering practice, said "it has the greatest potential of anything I have designed, the contents of your bowel, dried and turned into fuel. That fuel has 25 mega joules per kilogram - higher heating value than the best coal".

"Most coal in New Zealand is 10,000 BTUs, this stuff is 12,000 BTUs."

The system Mr Potter has designed dries sewage sludge to be used in place of coal, ideally by power stations, as a high quality fuel which has been deodorised, sterilised, and accepted by clean air authorities.


"Coal has 30-50 per cent carbon which is quite high and the dried waste has 15 per cent carbon which is quite low."

The sewage sludge is pumped from the settling tank, at 8 per cent solid, and put through a belt press to squeeze out moisture which runs back into the settling tank. The solids are then feed into the dryer using hot air - a similar process to drying coal. Once the first lot has been dried, it can be used to heat the water which dries the sludge.

Installation of the invention is expected in America later this year, and is hoped to attract worldwide attention.

Mr Potter said coal, oil, or gas are high in carbon and sulphur polluting the atmosphere, contributing toward climate change.

Once dried, the sewage sludge looks similar to a fine pepper with no odour. The by-product of drying the sludge is hot water, which can be stored and redistributed - reducing the hot water bill as it would come through the pipes hot, rather than having to heat using a hot water cylinder or gas.

"When it comes out it has 20 per cent solids, that is still 80 per cent moisture. In the drying process you can recover all of that water.

"What I am getting at is when you dry it, it can produce all the hot water we need. Every person produces about 70 grams per day of dried solids.

"It means when you dry it, all the heat [given off] can be recaptured, and turned into water. Each person can produce about four and a half gallons a day."

Having been in business for over 40 years, Mr Potter suffered a significant setback 10 years ago when he went completely blind. But that hasn't stopped him from thinking of new designs.