12:00PM, Thursday 12 November 2015
Ever thought about those little black food recycling boxes the borough gives us? What happens to the food collected? Reporter SIMON MEECHAN travelled to Wallingford in Oxfordshire to find out.
The little black box is the council's must-have home accessory, which lets some clever science types turn your food waste into green electricity and fertiliser.
We all have one but some of us, myself included, have been guilty of forgetting about the diddiest of our council bins and neglecting to use it. Some of us might not even know we have one, or what it is for.
But the little box can be for life, and can certainly be for Christmas, when the mountains of food many of us have to throw away over the festive season can be put in it, collected by the council, and shipped up the road to a farm in Oxfordshire where the magic happens.
Most food can be recycled, but the borough asks that milk, liquids and heavy packaging are not put in the food caddy. The waste can be put in free green food bin liners supplied by the council, before it goes in the bins.
The Royal Borough sends its food waste to Agrivert's Anaerobic Digestion facility in Wallingford, Oxfordshire. Last year this totalled nearly 2,000 tonnes.
At the facility, which was built in 2013, the food collected is depackaged, macerated and digested in large sealed tanks.
This ultimately creates biogas, consisting mostly of methane, which is converted into electricity, and digestate, an organic fertiliser.
Contract manager Debra Barnacle explained once the food is all mashed and big particles are removed, it is heated up in big tanks into a 'sloppy food soup'.
She said: "It's warmed, agitated, broken down, like in our tummies, and it gives off gas. Unlike with our tummies, we like that."
Pretty much any food can go, including meat.
"Anything that makes you fat, this process loves," added Debra.
When I visited on Thursday, November 5, the pit where the food is first dumped before being macerated looked like a low-budget horror scene.
It was full of the south's carved pumpkins, which had been set out for Halloween decorations but never eaten.
On the same day, Royal Borough councillors Richard Kellaway and John Bowden added some unwanted Brussels sprouts to the mix – a scene I am sure will be repeated countless times over December and January.
Food can be stored there for three days, so Agrivert can handle peak deliveries. Ideal, you'd think, for the post-Christmas onslaught the facility should get if we use our black bins properly.
There's no way around it though, the smell that awaits you as you enter the facility is overpowering. But after about five minutes inside, you begin to get used to it, and appreciate what the food is doing.
It is essentially left to compost, before shifting panels force it into a machine, pulverise it, and separate it from any packaging, leaving a liquid in a bath. Bones, eggshells and other parts which have no energy value are removed in a machine, once all the food is stripped from them.
"What is in that bath really is our raw material," added Debra.
After 90 days being heated up in large tanks, the bacteria has digested the food, and produces the biogas as a result. The fatty acids are removed, so the resulting fertiliser loses some of its odour. The liquid has been pasteurised to make sure there's no trace of E. coli or salmonella, as Agrivert is strictly audited by an number of bodies, including the Department for Environment, Food & Rural Affairs and the Environment Agency.
The fertiliser – 50,000 tonnes a year – is then used on fields near the site, instead of transporting it for miles, which keeps carbon emissions down.
The facility works 24 hours a day, and is 'fed' every four hours.
The biogas is used to fuel a large engine, which powers an electricity generator. The waste heat from gas engines is used to help heat tanks for the digestion and pasteurisation process.
Agrivert sells its electricity to SSE, with enough generated to power more than 4,800 homes. In total, 4.5 million cubic metres of methane are captured every year in the facility, which has the same greenhouse gas impact as removing 71,000 cars from the road.
According to the Renewable Energy Association, if all the UK's domestic food waste was processed by anaerobic digestion, it would generate enough electricity for 350,000 households. That's a city the size of Cardiff we could power just using our food waste.
I've dug out my box – I'm converted.
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