We can convert the food we bin into energy. But there’s a better, cheaper alternativeby Tristram Stuart / September 23, 2009 / Leave a comment
Above: for every tonne of food waste, 110kg of carbon-dioxide emissions can be saved by turning it into 255kWh of electricity
When I arrived in the small town of Ludlow to visit western England’s pioneering anaerobic digestion plant, I knew I was in the right place from the whiff of bins. The smell came from a huge warehouse surrounded by 10-metre tall metal tanks. Heaped up in the loading bay were thousands of bags of decomposing food waste. A closer look provided an insight into the town’s eating habits: half-eaten bananas, cabbages and unopened loaves of bread.
Run by BiogenGreenfinch, this is one of a new generation of anaerobic digestion plants designed to deal with the food-waste crisis while also generating clean, renewable energy. Inside the metal tanks, microbes that thrive in the absence of oxygen break down the organic matter, releasing methane as they do so—just like the microbes that create the bubbles of smelly gas that children stir up from the bottom of muddy ponds. After millions of years of hiding in dank recesses, these microbes have taken centre-stage in the struggle to deal with unwanted food.
From the loading bay, the waste is pulverised and then pumped through four processing tanks. These are connected to each other by pipes channelling gas, fluid and solids to their respective destinations. Once the microbes have done their work, over the course of a month or so, the organic waste comes out as peat-like compost and liquid effluent which farmers collect to spread on the land. The methane is burned to create electricity and hot water, or it can be pumped directly into gas mains, or bottled and used as vehicle fuel.
For every tonne of food waste, the Ludlow plant generates 255kWh of renewable electricity, which it sells to Marks & Spencer, saving 110kg of carbon-dioxide emissions. A government-commissioned study in 2007 estimated that if this system were extended to all households, it could provide between 0.5 and 1 per cent of Britain’s domestic electricity. Plus, this would avoid sending the waste to rot in landfill sites, where the methane can escape into the atmosphere, acting as a greenhouse gas 21 times more potent than carbon dioxide.
Under the EU Landfill Directive, Britain must reduce the amount of biodegradable waste going to landfill to 50 per cent of 1995 levels by 2013. The National Audit Office has warned that…