25th August 2022
The Darenth Valley’s Biogas Powerplant
by Erica Russell on behalf of the Green Team
Visiting a large scale anaerobic digestor is not a usual agenda item for the Parish green team but we were all curious to find out more about the ‘mini powerplant’ that has been built near Horton Kirby. Firstly, what is it?! This particular powerplant is driven by anaerobic digestion. This process relies on bacteria and microbes to break down plant material to create biogas, which in turn can be treated to allow the gas to be used for heating and cooking or to produce electricity. The process also creates biofertilizer than can go back onto the land. Across the UK anaerobic digestors recycle 2.5m tonnes of food waste each year.
The site is large, much bigger than any of us had expected. Oncoland Energy have spent over £10m on the plant and it’s run by a full-time manager and two staff. Initially designed to help spread the risk of fluctuating crop prices the digestor is also helping manage difficult agricultural waste, some of which produces large amounts of atmosphere warming gas – methane. Many of us in Eynsford will be familiar with at least one of the feedstocks used by the digestor – slurry from Bower Lane Farm! But, the site also takes in a lot of waste parts of crops, unwanted/oversized produce, including and rather surprisingly waste pomegranate skins. Carl explained that the site is working hard to develop relationships with local food processors to take on similar materials. The farm also grows some crops themselves to balance the nutrients within the digestor.
Digestor is a good description when thinking about how the process works – the feedstock is mashed and chopped up in a large machine (the mouth), fed into ‘the stomach’ through pipes, with biogas drawn off from the large digestors and then the odourless biofertilizer ‘waste’ is moved out into storage bays, before being used by local farms – very little is wasted.
Treating the biogas is complex and heavily regulated but the site is now producing enough back to the gas network to heat 2500 homes. The plant also has a small generator which, fuelled by biogas is putting electricity into the grid – about enough to light around 600 homes a year.
It was a fascinating visit, and we must give huge thanks to Carl Woolley, the site manager, who gave up his evening to show us around and explain the process.