A load of rubbish

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A load of rubbish


We can convert the food we bin into energy. But there’s a better, cheaper alternative

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 Britain is at risk of failing to meet the target, which would result in crippling fines, passed on to local councils, of up to £1m a day. So the government is belatedly pouring funds into new large-scale anaerobic digestion plants. Whitehall dished out £10m in grants this year; the Welsh assembly a further £26m. Extra assistance comes from the government’s renewable obligation scheme, under which, for every unit of electricity they produce, plants receive twice as much extra money as other sources of renewable energy. And now the government is considering an outright ban on sending food waste to landfill.

The problem is that anaerobic digestion plants are expensive to build and complicated to run. The Holsworthy plant in Devon, for example, cost £8m to build. The government paid half yet the business still went bust. And plants across the country charge “gate fees,” averaging £60 per tonne of waste. Customers are willing to pay this in order to avoid the government’s £40 per tonne landfill tax. In effect, the tax regime provides the financial backbone of anaerobic digestion. Studies in the US have shown that anaerobic digestion needs support to be profitable. Enthusiasts forget that turning food waste into energy is not an economically viable primary industry in itself: it is a service that must be paid for.

More worryingly, the attention fixed on avoiding landfill has distracted government and businesses from the far more crucial step of reducing the amount of food wasted in the first place. Britain produces up to 20m tonnes of food waste annually. But not one of the supermarkets has yet set a target for reducing it in their supply chains. The energy recouped by sending waste, such as a tonne of tomatoes, to anaerobic digestion is just 0.75 per cent of the energy needed to produce the food in the first place. The most important measure, therefore, is to stop wasting food.

There’s another disposal method which is cheaper and better for the environment: it’s 9,000 years old and is called swill—food waste fed to pigs and chickens. Swill can save up to 520 times more carbon emissions than anaerobic digestion, and the retail value of the pork produced could be worth around nine times more than the energy. And there is almost infinite capacity to deal with food waste in this way available now: our cash-strapped pig farms that are going bust thanks to the high prices of conventional feed. Farmers in 2008 lost around £20 per pig produced.

It is right to boost Britain’s anaerobic digestion industry, but pig farmers who want to use bread, vegetable and dairy waste as feed should be getting comparable assistance. The government should also lobby for an end to the EU ban on feeding sterilised swill to pigs and chickens. As numerous scientific papers have shown, the animal health risks associated with swill-feeding can be controlled by heat-treating the waste. The Japanese and South Korean governments fund factories that convert food waste into livestock feed. If the government does not do the same, its “green” policy could skew the food-waste management market in ways that might be less good for the environment.

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  1. Food to Energy Plants: A Load of Pig Swill? : Green Resouces10-05-09
  2. Waste of energy? (A Monday morning blogrant) « isite11-23-09


Tristram Stuart

Tristram Stuart is the author of "Waste: Uncovering the Global Food Scandal" (Penguin) 

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