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Biogas from organic waste



Welcome to the onsite power systems UC Davis Biogas Energy Project.An advanced technique that will take organic waste and create sources of renewable energy and biofuels that will help reduce our state's and country's dependence on foreign oil. The biogas energy project demonstrates an advanced anaerobic digestion technology capable of processing high solid and high liquid waste matter. The advantage of this system is that traditional digesters can only handle high-liquid waste, and this system can handle high-solids, including grass clippings and food waste without any sort of pre-processing. The waste goes through two stages in the anaerobic digestion process. The first stage breaks down the material and makes water and organic acid. The second stage takes those organic acids and makes methane gas. The two stages of the digestion process have different types of bacteria strains. The first step's bacteria is very hardy and can survive under almost any conditions, whereas the bacteria in the second stage that make the biogas are very sensitive to temperature and pH. This process separates those two stages, allowing each bacteria type to have an optimal environment. First we load the organic materials into a tank, allow it to break down at its own rate. As the material breaks down it produces water and organic acids. We take the water from the tank and decant it and feed it to a second tank where the bacteria that make the methane gas are housed. In that tank, or the gasification tank, we keep the optimal environment for the bacteria: 135 degrees Fahrenheit and a neutral pH level. At regular intervals we'll take water from the first stage tanks, along with the right amount of acids to feed it to the gasification tank. With this we get a very steady production of biogas. Typically food waste will break down in 5-7 days, green waste in 10-12 days, and we let the material stay there as it creates the water and the acid, and then we feed it to the gasification tank.



Pune, one of India's silicon cities. An unlikely home for biogas development, a fuel usually linked to cow dung and rural energy supply. But one man's vision is turning conventional wisdom upside-down, proving biogas may yet be an option for the city dweller.

The Appropriate Rural Technology Institute, ARTI, has developed a revolutionary approach to produce methane. The new method is much more efficient than the traditional one and doesn't need dung. Our system is four hundred times more efficient than the dung-based biogas plant. This is like any normal biogas plant where you have a fermenter here and a gas holder here. ARTI has found that the bacteria will eat leftover food instead of dung. This household has expanded their system to two inter-connected tanks, allowing them to use biogas as their main energy source. "I only use the LPG now to heat bath water. I cook all our meals just using biogas." Mohan Carti collects leftover food from his neighbors. The leftovers have to be left to ferment for a few days or mashed to a pulp before being fed to the bacteria in his rooftop biogas tank, providing the perfect solution for organic city waste, which is just left to rot as landfill space is limited. "We use that effluent as fertilizer." It takes just two days to produce the gas rather than a month. There's another advantage to not using dung that really appeals to city dwellers. "We are studying here, just a few feet from the plant, but can you smell anything? No, there's no odor."



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