“Biogas is now going the same way [than biodiesel]. Provide the money to do the right thing and if you're not careful it will be used to do the wrong thing.
Part of the problem is that there's not enough money on offer to make the conversion of waste alone economically viable. That's because the yields of gas are often quite low. For example, slurry from cattle and pigs produces only 15 to 25 cubic metres (m3) of biogas per tonne of material. Purpose-grown crops are much more productive. Grass silage produces 160-200m3 per tonne, while silage made from maize (which in the US is called corn) generates 200-220m3, and potatoes 280-400m3.
Economic modelling commissioned by the government tested eight different mixes with which farmers could feed an anaerobic digester, to try to work out which were profitable. All of them included grass, wheat, maize or potatoes, and in some cases the models specified a higher tonnage of these specially grown crops than the waste the digesters are supposed to process. As maize has both a high yield per hectare and a high yield of biogas per tonne, it has become what the farming press calls the biogas "core crop". There could scarcely be a better formula for subverting everything biogas is supposed to achieve.
(...) If you want to know where we might be heading, take a look at Germany. Two years ago Der Spiegel reported:
"Subsidies for the biogas industry have led to entire regions of the country being covered by the crop … Plans called for transforming Germany into a bio-wonderland by peppering it with numerous small eco-power plants. What resulted was a revolution in the fields, a subsidised gold rush – and an ecological disaster. Corn [maize] is now being grown on 810,000 hectares in Germany."
As a result, "for the first time in 25 years, Germany couldn't produce enough grain to meet its own needs."
(...) In other words, it's the biodiesel story, all over again. Because the anaerobic digestion of waste food and slurry makes sense, I don't want to see a biogas moratorium imposed. But I would like to see a ban on the use of all purpose-grown feedstocks. To make biogas viable, this ban would have to be accompanied by an increase in the subsidies available for converting waste. Yes, that means extra expense, but it's got to be a better deal than trashing the food supply, the soil, the rivers and our living rooms – all in the name of protecting the planet.” From How a false solution to climate change is damaging the natural world by George Monbiot, The Guardian, March 14, 2014