Anaerobic Digestion (AD) is a natural bacterial fermentation process that converts waste organic matter such as food leftovers, garden waste or even paper into methane and leaves a residue of organic matter that can be used as a fertiliser. A modern AD plant is an efficient way of dealing with this material, as it converts potentially problematic waste matter into something useful. As the process happens under controlled conditions, there are no problems with odours or vermin. Further information on AD can be found at www.biogas-info.co.uk or www.anaerobic-digestion.com.
Our AD plants require approximately 2,400m2 of land to build a reception building for the food waste and a primary and secondary digester that use a batch–separated thermophilic digestion process. The food waste is shredded, screened and heated to meet pasteurisation regulations and once it reaches the digesters no further odours are produced. Digesters can be made of stainless steel or concrete.
Combined Heat and Power
Positive Energy Sussex will be using AD to produce biogas which will then power a CHP engine. A CHP engine produces both heat and electricity from a single fuel source. CHP comes in many forms – for example your car heater uses waste heat from the engine to heat up the interior. This is a very simple form of CHP.
Conventional power generation generally wastes any heat that is produced during the process – visualise the steam rising out of cooling towers at large power stations. The biogas CHP engine turns the biogas fuel into electricity which is fed into the national grid or used locally, but the heat produced from the process of making the electricity is also harnessed and put to good use. It could heat a building for example, or it could supply hot water. A modern CHP engine will usually supply more heat than electrical energy. If we use both we are using around 92% of the energy generated.
Further information on how CHP engines operate can be found on the Department of Energy and Climate Change’s website, or on the Combined Heat & Power Association’s website.