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7 Biogas p.276

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Objectives Students should learn: that biogas, mainly consisting of methane, can be produced by the anaerobic fermentation of waste materials containing carbohydrates that when biogas is burnt it can provide energy for domestic and industrial use that different designs of biogas generators are suitable for different circumstances.

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Outcomes Most students should be able to: describe the nature of biogas explain how biogas is produced in a generator. Some students should also be able to: evaluate the advantages and disadvantages of given designs of biogas generator.

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Specification Biogas, mainly methane, can be produced by anaerobic fermentation of a wide range of plant products or waste material containing carbohydrates. Evaluate the use of biogas generators.

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Biology B3 4.7 Biogas Answers to in-text questions a Methane b One in which energy is released. Summary answers 1 Biogas is a biofuel and is mainly methane with varying amounts of carbon dioxide, water and other gases. It is made by bacteria anaerobically breaking down plant and animal waste material that contains carbohydrates. 2 a More than one generator is needed. As one is being cleaned out, another is producing gas. b A batch-type digester will use plant material rather than the waste needed for the other types shown. In some places animal waste may be in short supply, or there may be religious or hygiene objections to using waste, yet the batch digester can still be used to produce biogas.

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Workbook P. 127-9

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Compulsory slides you must complete and use;

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What is biogas? Explain from text p.276

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that biogas, mainly consisting of methane, can be produced by the anaerobic fermentation of waste materials containing carbohydrates (explain p.276) How is biogas produced

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How is biogas used? domestic industrial

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How the design of a biogas fermenter is adapted for its circumstances

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Fun activity Compare a biogas fermenter with a chocolate teacake Similarities? Differences/bits missing

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Some slides you may wish to use

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What is biogas? Biogas is a gas produced by the anaerobic fermentation of organic waste containing carbohydrates by bacteria. This gas contains: 40%-70% methane carbon dioxide traces of hydrogen, nitrogen and hydrogen sulphide. Biogas is currently used in several ways, including in the production of electricity, heating water for central heating systems and as fuel for buses.

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Producing biogas

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Biogas use in remote areas In parts of rural India cow dung is used to produce biogas for cooking. The production of biogas can be ideal in remote areas lacking mains electricity or sewage systems. It not only produces a useful fuel but can also be used to get rid of large quantities of sewage or other organic waste material. On a small scale, biogas digesters can be used to provide energy for individual families or farms.

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Biogas B3 3.6 How is biogas produced?

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Cows in India have a poor diet. They produce large amounts of methane in the wind they pass from both ends of their bodies. The manure they produce also produces some methane if it decays without enough air. Collecting the methane directly from the cows is not very practical but we can make use of the manure!

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Scientists working at this village in India have developed a biogas digester that can make methane from a mixture of cow manure and other organic waste. It is providing useful gas for local people for heating water and cooking food.

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The biogas digester is a huge upturned metal drum. Waste is pushed underneath through holes in the concrete base. As the manure decays in the absence of air, the methane bubbles to the top and passes to storage tanks through a metal pipe.

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The biogas digester is sealed with a layer of oil around the base. You can just see the leaves from the tree overhead reflected in the surface. The oil keeps oxygen out so that the decay is anaerobic. The metal drum floats up and down as the gas is produced. The frame has guides with small rollers on the ends to let it move.

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The system is so good that development workers and scientists from around the world come to visit and find out how it works. This picture shows visitors from several African countries, a few from South America and some from Asia. Link to methane powered streetlights in China

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A Generalised Biogas Generator Biogas generators take in waste material or plants, and biogas and useful fertilisers come out the other end. Airtight so process kept anaerobic

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Fixed Dome Biogas Plant Advantages Low initial cost Long useful life as no moving or rusting parts involved Well-insulated Disadvantages Sealing of the gas holder not always gas-tight Gas pressure fluctuates

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Types of biogas generator used by this company