Anaerobic digestion (AD) has revolutionised the way that food waste can be handled on a commercial scale. No longer is it lost to landfill, as specialist recycling companies now convert it to energy for homes and businesses.
One such company is Biogen, who operate 7 recycling centres around the UK and its latest operation, located near Atherstone, Warwickshire, processes over 45,000 tons of food waste every year!
Over 110 tons of food waste is delivered every day, where it is bulk loaded into a ‘de-packaging’ line, to separate the food waste from associated packaging. The food waste then travels through a series of processing operations, to prepare it for the AD process.
Two anaerobic digesters operating at 40 °C, complete a digestion cycle every 40 days, which ensures the maximum energy value is recovered from the waste. The AD process produces a combustible gas containing Methane CH4 (60%) and CO2 (40%), which is used to power the company’s two GE Jenbacher generators.
The electricity produced from the generators is fed into the National Grid and provides enough power for 4,500 homes.
Waste heat is also recovered from the generators cooling system and this is transferred through two Bowman FC160-1426-5 heat exchangers to provide hot water for three primary areas – building services, including the underfloor heating system, plus personal hygiene facilities; the waste packaging ‘hot wash’ process, to remove any remaining food waste and avoid cross contamination; plus jet washing of all commercial vehicles prior to them leaving the site.
Remaining solids are sent off site for further processing, whilst remaining liquids provide a nutrient rich fertiliser for local farmers, ensuring that literally no waste material is sent to landfill.
‘The Bowman heat exchangers perform a vital role within the plant’ said site manager Kevin Eagles, ‘they not only cool the generator engines, they also provide hot water for vital process cleaning operations and ensure the offices and staff areas are always warm and comfortable’.
