8.3 million tonnes of food is thrown away by households in the UK every year. Wasting food costs the average family with children £680 a year and has serious environmental implications too. [For more information visit the Love Food Hate Waste website].
Anaerobic digestion is the natural breakdown of organic materials such as our food waste into methane and carbon dioxide gas and fertiliser. There has been a lot of controversy over the new Anaerobic Digester recently opened in nearby Cassington to handle food waste. It was feared that the site would look unsightly, smell and cause the area to be over-run by waste lorries. Oxfordshire Waste Partnership, the Earth Trust and contractors Agrivert recently teamed up to hold an open day at the Cassington plant which was attended by Kidlington vs Climate Change member Janet Warren. Janet is KvsCC’s food champion; she is passionate about sourcing and promoting local seasonal food and fights our corner in the ‘War on Food Waste’.
Here is Janet’s reports on what she saw.
”Silage: the bug world’s Alka Seltzer
Those who inhabit Ambridge for 15 minutes a day (The Archers, Radio 4) may already know about anaerobic digesters (ADs); the topic was aired in 2007. However, I now realise it didn’t quite capture the full picture but that was put right when, as a member of Kidlington vs Climate Change, I joined a conducted tour of the AD site run by county council contractors Agrivert at Cassington.
I was expecting it to look grim; to smell disgusting; and to be overrun with lorries. WRONG, WRONG, WRONG. The buildings were smart; there was absolutely no smell; and our party saw only a couple of lorries while we were there. Bringing in waste from far afield or taking fertiliser out further than is necessary would be against Agrivert and Worton Farm’s environmental business aims so transport is kept to a minimum. The site was so well controlled that it could have been managed remotely, we were told, from a home computer. Sadly for him though, the manager was expected to come in every day.
The site takes solid & liquid food waste from local food businesses, as well as from local households. The liquids are ducted straight into underground tanks so there was nothing to see there. But we did see the solid waste starting off on its journey of transformation.
The solid waste is tipped into a huge bin where, first of all, contaminants such as metal and plastic are mechanically removed to prevent damage to the machinery. Interestingly, the waste from domestic sources is 99% compliant i.e. no contaminants. The mix is then pulverised to produce the liquid food waste that is drained off for digestion. This part of the site does have a bit of a pong to it but the smell does not escape outside as the air is bio-filtered before venting.
Unwanted bugs are eliminated from the liquid by pasteurisation, using waste heat from the gas engines at the other end of the process. It is then pumped into digesters, where “useful” bugs take about 100 days to eat up all the nutrients, creating methane as they go and eventually dying of starvation. The remaining liquid is a much valued fertiliser rather like Baby Bio. That is just what it looked like and smelled like. The liquid is stored on-site underground until the farmer is ready to use it. Needless to say, there is no shortage of willing takers, especially as using it is much easier on the nose than traditional muck-spreading!
Finally we saw the on-site gas engines which generate electricity for the national grid, enough to supply electricity to about 4,200 homes. The left over solids are turned into compost and so the only waste from the process is the unused heat generated by the gas engines, but there are plans in the offing for using that too.
The silage? Well, just like humans, bugs need a good balanced diet. If the diet gets monotonous or the bugs get a bit sluggish then a dose of silage will perk them up! “
For further information on organic waste disposal in Oxfordshire c an be found at http://www.agrivert.co.uk/assets/news/CassingtonAD-Press-Brief.pdf