Brazilian vehicle fleet drives on bio-methane from the sewage plant

Great potential for the use of sludge gas for mobility in Brazil

The wastewater treatment situation in Brazil differs greatly from that of Germany. Although the majority of the population in industrialized areas such as the state of São Paulo (SP) is connected to the sewer system, a large amount of untreated sewage nevertheless flows into receiving waters. Due to Brazil’s Growth Acceleration Programs, wastewater treatment technology will undergo further development in the future. At present, the sludge gas produced in Brazilian sewage plants is not, as a rule, systematically used, but rather burned in open flares.

According to the IANGV (International Association for Natural Gas Vehicles) Brazil owns one of the world’s largest natural gas vehicle fleets along with a huge network of natural gas fuel stations. In 2009, its 1.6 million vehicles enabled the country to come in fourth behind Pakistan, Argentina, and Iran. With regards to its 1704 natural gas fuel stations, Brazil even took third place. As early as in 2003 flexible fuel vehicles were introduced into the Brazilian market and currently constitute 87 percent of all new registrations. These vehicles can be run on gasoline, methane, ethanol and also a mixture of these fuels. Converting the tanks of such vehicles also enables the use of natural gas as a fuel source. The Brazilian market already has a factory-converted Tetrafuel vehicle which runs on pure gasoline, Brazilian gasoline (with 20 percent ethanol), ethanol and compressed natural gas.

Exploiting sludge gases from Franca’s sewage plant

As a part of international efforts geared towards climate protection, the BMU supports selected projects in partner countries, which contribute to the reduction of greenhouse gas emissions. Such is the case with the project of the Fraunhofer IGB with the Brazilian water provider and sewage disposal company SABESP. The project aim is to gather the sludge gases produced in the city of Franca’s sewage plant, operated by SABESP, and purifying it until it reaches the quality of natural gas (bio-methane). This product, considered today to be one of most environmentally sound fuels in existence, shall in turn be made available to a fleet of vehicles. The benefits of this fuel are truly great due to its balanced carbon footprint – its combustion creates virtually no new greenhouse gases.

Approach

In order to reduce the bureaucratic hurdles involved in such an endeavor, the project was registered under the German-Brazilian Framework Agreement on Technical Cooperation. Project implementation can be subdivided into categories such as process selection, determination of required design data, determination of exact location, basic and detail engineering, machine assembly and operation, vehicle conversion and staff training.

Results

The sewage plant in the city of Franca is run by using the activated sludge process and operates with two sludge digestors. These produce an average of 2700 m3 / d of sludge gas which is burned in two open flares. Based on our analysis, methane levels rise somewhat higher than 60 percent. With a methane content of 60 percent and a calorific value of 10 kWh / m3, approximately 1600 L / d of gasoline can be replaced. SABESP plans on having 49 vehicles converted to have them run on bio-methane. It is expected that the city of Franca will add some of their own to that total.

Since the ferrous sludge from the waterworks is also processed in the digestion process, the concentration of H2S is very low. This simplifies the purification of the sludge gases. Conceived and designed by our own team, the concept for purifying the sludge gases and exploiting the resulting bio-methane is currently being installed at the existing sewage plant. The latter is in turn being expanded to include a double-membrane gas tank, a pressure swing adsorption in a container used for gas purification and generation of bio-methane as well as a bio-methane gas station with high-pressure tanks for fuelling converted vehicles. By summer 2012 the plant will begin operations and be run by the sewage plant staff. The general appearance of the plant can be seen in the diagram on the left.

Outlook

Both the reduction of methane emissions from the sewage plant as well as the replacement of fossil fuels with bio-methane will serve to reduce greenhouse gas emissions. Should the project prove a success, SABESP plans to equip more plants with similar technologies. We furthermore expect this project to convince other operators of sewage plants and disposal sites and communities in Brazil to choose the path of sustainability and use bio-methane as a fuel source.