Brazilian town turning human waste into clean energy

High in the cool hills of eastern Brazil, this tourist hot spot also known as the Imperial City is attracting worldwide attention thanks to an innovative scheme to recycle human sewage.

It has fostered a relatively simple idea now gaining traction in other parts of Latin America and as far afield as Spain, as nations struggle with the impact of burgeoning populations compounded by dwindling supplies of fuel and water.

Here bio-digesters - specially designed organic enzymes and bacteria - are used to break down waste water and turn it into alternative energy sources such as gas.

During three fermentation processes, the bio-digesters are unleashed on human effluent and as they break it down they produce a bio-gas, a mixture of methane and carbon dioxide, which can then be piped into homes for use in heating or cooking.

"In fact this is a greenhouse gas, which is harmful to the atmosphere when it is unleashed, but can be collected to be useful," said Jorge Gaiofato, technical director at the Environmental Institute, the non-governmental organisation behind the scheme.

Today there are more than 80 such bio-digesting ponds in Petropolis, a town some 65 kilometres from Rio de Janeiro on the east coast, which was once the summer residence of the Brazilian emperors in the 19th century.

The results of this 21st century project are generating a lot of interest. Nicaragua, the Dominican Republic and Haiti have all established similar schemes.

The beauty is that nothing - literally - goes to waste. The mud left over from the bio-digesting process can be used as fertiliser for crops and the remaining water, now cleaned of noxious elements, is emptied back into neighbouring rivers.