Petropolis, Brazil, a small town 45 miles (65km) from Rio de Janeiro, is a tourist hot spot that has turned its human sewage problem into a solution for clean energy. The town has built more than 80 bio-digesting units designed to capture the methane gas and carbon dioxide released by sewage. In the past, a lack of sufficient sewage treatment facilities has been a problem for the area, as it is in many developing countries.

During a three-part fermentation process, natural bacteria and enzymes are added to the human waste generated by the town. The bio-digesting process then releases the gases to be captured for heating and cooking uses. These greenhouse gases would have been released into the atmosphere, but are now being captured and used safely. This bio-digestion network provides clean energy to 5 of the city’s poorer areas, including cooking and heating gas for over 20,000 people.

After the bacteria and enzymes have completely broken-down the waste and the gases have been captured, the by-products are bacteria-free water and a mud that can be used as fertilizer for crops. In developing countries where populations are rapidly growing and few municipal sewage facilities exist, this and similar bio-digesting facilities are becoming very popular while helping save the environment.

Some green-wise homeowners in developed areas of the world have replaced their traditional septic systems with bio-digesters and are using the gas for heating and cooking. The bio-treated water by-product is odorless and is being reused to flush toilets again. Bio-digesters also help prevent water contaminated by sewage from running into our fresh water supplies.
Some livestock farms in the US have installed commercial bio-digesters as a way to recycle the massive amounts of animal waste produced daily by cattle and pigs. Large livestock operations have been under fire in recent years due to the greenhouse gases released by animal waste and the rainwater run-off that has been contaminating our streams and rivers.

In some cases, the methane gas collected by these huge bio-digesters is being used to run modified diesel generators that provide all of the power required to operate the farm 24 hours a day. It is estimated that the daily manure from 5 cows can produce enough gas to generate 1kw of electricity. More advanced bio-digestion operations produce a by-product that can be used as odor-free mulch or animal bedding.