As the costs of landfills rise and the worry of powering our future increases, it is clear that we are all producing too much waste, and using too much power in doing so. Whilst recycling can make a huge difference towards the amount of waste we simply throw away into the earth, there are now new ways of not only getting back recycled materials from our waste, but also, specifically in food waste – energy and fertiliser.
Anaerobic Digestion
Anaerobic Digestion or AD is a natural process that biologically breaks down organic material to produce large amounts of biogas – a combination of methane and carbon dioxide. Much like the compost heap in your garden, AD works in the same way only on an industrial scale and in the absence of oxygen to allow the capture of biogas.
How does it work?
As far as turning consumable food to energy, which sounds mightily impressive, the process is relative simple. Thanks to ReFood.co.uk, here’s the entire process in 8 steps:
Food waste pre-treatment
All food waste collected is emptied into hoppers before going through a de-pack process, which separates the packaging from the organic waste. Once plastics and packaging are removed, they’re cleaned and sent away to refuse-derived fuels. Liquid is added to the organic waste so that it can be easily pumped.
Heating
All the food waste, with added liquid, is then passed through a heat exchanger and heated to around 70°C using entirely recycled heat.
Pasteurisation
The waste is then held at 70°C for one hour, to comply with ABP regulations.
Cooling
After an hour, it is cooled by passing it over the incoming material. This takes it back to approximately 40°C.
Mixing
The waste is then moved to a mixing tank, holding 3 days of material and ensuring that a uniform product is transferred to the digesters.
Digestors
Digestor tanks are fed in turn, each one holding around 3,500 tonnes of material. The material will stay in these tanks for 30 to 35 days and, in an absence of oxygen, bacteria works it’s way around and breaks down the food waste, producing methane gas.
Gas collection
Gas is then collected from the top of the digestors and passed through a biological scrubber, where the bacteria filters it to remove Hydrogen Sulphide which damages the engines
Screening, storage & dispatch
Gas is then stored in storage tanks until it is required. It is then pre-conditioned to remove water, cooled and pressurised before being fed to engines which produce enough electricity from one plant to power around 5,000 homes an hour. This power is all fed back into the national grid.
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