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Anaerobic Digestion is a natural biological process where organic material, in our case food waste, is broken down by bacteria. It is similar to composting but differs in that it takes place in sealed, oxygen-free tanks to produce biogas that can be used to generate electricity and heat. Currently, much of our biodegradable waste is sent to landfill, where it breaks down to release methane, a powerful greenhouse gas. AD helps tackle climate change by diverting this waste from landfill and incineration.
On site we are utilising the heat generated by the CHP jacket water to maintain the right temperature for our large digesters, each holding 3,500 tonnes of food waste slurry. This creates the best environment for the friendly methane generating bacteria. Heat is also collected from the CHP exhaust flue to help run the pasteurisers, and by pasteurising before the material enters the AD process, this ensures the health of our system and protects against bacterial contamination.
Other exciting technology includes a mixing system with both, pumped jets of slurry and gas recirculation, for complete mixing and no in-tank components, meaning all maintenance is carried out seamlessly. Our H2s inhibitor detects when H2s is building up and pumps air into the digesters. This air feeds a bacterial culture on a net in the gas lid which eat the H2s. The results are dramatic and their biogas contains on average 30 parts per million (ppm), when up to 500 ppm is normal, this extends the life of the CHP and components. The biofilter ensures no odours escape into the local area and manages 3 air changes per hour of the Reception Hall.
A proportion of the renewable electricity generated is used to drive the electrical systems on site, such as the waste shredders, de-packaging machinery, material conveyors, control systems and of course the myriad pumps and valves that move the resulting food waste slurry through the AD process. In due course Bio Dynamic will install Solar PV on the roof of the waste reception building and it is calculated that the area of roof space available, being east/west orientation, will provide enough power to satisfy site demand during daylight hours.