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Chapter 7  Plastic Biogas Plant Designs

There are two main types of plastic biogas plant: ones that use flexible plastic and those that use rigid plastic to make plants that are similar to floating drum or underground plants. Flexible plastic systems include "bag" digesters, where the whole plant is made from plastic and "membrane" digesters where the plastic membrane acts as a gas holder over a pit made from masonry or other materials. Floating drum designs also include systems in which the tank and gas holder are both made of plastic (Martin, 2008; Roos et al., 2004) or ones in which only the gas holder is of plastic and the digester tank is made from masonry or other materials. Underground plants are also available in which the digester pit and reservoir are both made of plastic.   


Chapter 8  Ancillary Equipment

Ancillary equipment used with a biogas plant includes slurry and gas handling equipment. Inlet slurry of dung and water can be mixed with various types of machine. Food waste often requires a pre-digester. Outlet slurry should be used as a compost. Gas equipment includes pipes, valves, manometers, stoves and lights. Gas pipes can be made of several different materials, such as metal (steel or copper) and plastic (HDPE, PVC, etc). The best valves to use for gas are ball valves. Gas stoves and lights need to have been carefully designed and tested. Biogas can also be used in engines with suitable ancillary equipment.  


Chapter 9  Using Biogas Plants

The process of building a biogas plant involves a series of decisions: the design of plant to be used; the feed stock available and therefore the size of the plant; the location of the plant and its distance from the feed stock supply; and where the gas is to be used. Starting a plant involves adding the right microbes and allowing the population to be built up. Running a plant is a matter of feeding it regularly and avoiding contaminants.


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