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ENERGY-BRAZIL: Putting (Human) Waste to Work

Fabiana Frayssinet

PETROPOLIS, Brazil, Oct 6 2009 (IPS) - Biodigester technology, which originated in Asia as a natural process for treating sewage waste, is reemerging in Latin America as an integrated system providing cheap energy, improved sanitation, and even attractive landscaping.

It is hard to imagine that beneath a delicate flower floating on a tank full of crystal-clear water, there is a hidden biodigester treating waste from a family home.

Even more difficult is to imagine that a small two-ring cooker, where a mother prepares rice and beans for her young children, is fuelled by gas produced by the biodigester.

But at the home of architect Jorge Gaiofato, the connection between ugliness and beauty, waste and useful materials, and what is nauseating and what is delicious, is not only imaginable but proven in practice.

“The Chinese were already using this technology over 300 years ago. Our purpose is to show that it is easy to treat the waste products of human consumption, and at the same time to produce wealth from the process,” he told IPS.

At his home in the middle of a lush forest in the Serra de Petrópolis, in the state of Rio de Janeiro, Gaiofato practises what he preaches as technical director of the non-governmental Environmental Institute (OIA).

Surrounded by streams and waterfalls, the house uses the biodigester sewage treatment system as part of a more complex, yet simple, process called an integrated biosystem.

“The Environmental Institute had previous experience with treating waste in systems of water tanks using different varieties of plants, and when the biodigester came along, it combined the two systems,” he said.

“So now we have the biodigester performing the anaerobic part of the process, and the plants doing the aerobic part. This is what we call an integrated biosystem,” he said.

The words used are unfamiliar to the non-specialist but the process is simply natural, imitating, according to Gaiofato, “the sustainable cycles of nature, which reuses materials for a new cycle of production.”

“Instead of expecting the earth to produce ever higher yields, we must learn to do more with what the earth produces,” according to the OIA.

Sewage waste is piped to the biodigester, a hermetically sealed tank which is located as close as possible to dwellings.

Biodigesters ferment the organic material and produce biogas, a mixture of 74 percent methane and 26 percent carbon dioxide. The gas is piped back into the home, where it can be used as fuel for heating, cooking and lighting.

The process inside the biodigester is biological, said the architect. “It is carried out by anaerobic bacteria, that is, bacteria that live in conditions where there is no oxygen. Several types of bacteria break down the organic material, and in the last stage, methanogenic bacteria convert it into methane gas,” he said.

The biological solids that are produced by the same process have a high nutrient content, and can be separated, sun-dried and used as organic fertiliser on plants.

The liquid slurry from the biodigester can be filtered several times and used for “fertigation” – added to an irrigation system for fertilising crops – or for general cultivation purposes.

“Nutrient recycling” begins with a second tank where plants absorb nutrients from the treated slurry through their roots.

In a third container, residual nutrients are absorbed by aquatic plants.

Finally, in a sunlit pond, the remaining nutrients feed the growth of algae, which in turn are eaten by fish, like tilapia – a source of food.

A simpler and cheaper version of the system, to provide sanitation and supply energy for a local community, consists of just the biodigester, which can be hidden from sight by burying most of it underground.

Biogas has several uses, including fuelling conventional kitchen stoves, electric generators, garden lighting and water heaters.

According to OIA’s calculations, the average production of biogas is 50 litres per day, supplying a family’s needs for one hour a day.

Alessandra Fachini, who has a three-year old child and a baby, does not have to buy the cylinders of gas sold locally. Her biogas supply is enough for her daily cooking needs, and to run a small water heater and an outside light.

“If we want to conserve and use a sustainable resource that does not harm the environment, like natural gas, we have to re-educate ourselves and turn towards this form of use, which is healthier for everyone,” said Yuri, Fachini’s husband.

Gaiofato said that, with low equipment and maintenance costs, biodigesters treat sewage effluents, produce energy, and are good for the environment because they keep methane – a particularly harmful greenhouse gas – from being released into the atmosphere.

In Brazil, the OIA is promoting biodigester technology particularly in small villages of up to 500 people, where a community system can be installed. As well as in Rio de Janeiro, the organisation works in the states of Sao Paulo, Santa Catarina, Espíritu Santo and Bahia. It also has projects in the Dominican Republic, Nicaragua, and the region of Valle de La Plata in Spain.

At present, the OIA is spreading the concept of integrated biosystems in slums in Haiti, not only for sanitation but also for recovery of degraded soils, the construction of more sustainable housing and integrated crop systems.

Whenever they put in a biosystem, the organisation seeks to train the beneficiaries so that they can spread the technology to others in their community, and whenever possible the projects include environmental education for local people.