Anaerobic digestion for biorenewable fuel and fertiliser

17 Sept 2010

Conceptually, it is an obvious and virtuous solution. Anaerobically digest waste, then use the resulting biogas as a renewable energy source and the digestate as a nutrient-rich soil improver. It is not even a new idea; sewage sludge AD has been carried out for a hundred years. For 35 years, use of this digestate on farmland has been controlled to protect soil, crops, animals, water, humans and other possible receptors. Regulatory complexity has, however, inhibited extending this tried and tested technology to a wider range of feedstocks. As Einstein said: 'Any intelligent fool can make things complex ... It takes a touch of genius, and a lot of courage, to move in the opposite direction.'

The aim of SCI's highly successful 'Biorenewable Fuel and Fertiliser: Realising the Potential' event held in March 2010 was for representatives of the interested parties to debate the best and simplest ways to unlock AD's true potential. Held in conjunction with Fera, the full day of discussion focused on business opportunities around AD and provided delegates with a good understanding of the regulatory playing field.

The EU Landfill Directive will not allow any food or farm waste to be put into landfill sites from 2015. Initially, the UK government viewed energy and recycling as exclusive alternatives, but eventually realised that AD could provide both. It promoted AD with the zeal of a convert, but without learning from or seeking synergy with established practitioners. Typically, government dealt with processes rather than outcomes, and was indecisive about providing the required 'Renewables Obligation Certificates' (ROCs) to support 'green' electricity produced by AD.

The feedstock's legal status is an additional complexity. If it is 'waste', so is the digestate; but manure or crops grown to digest are not classified as waste. This was not conducive to investment in AD waste projects. Thankfully, the stealth tax on using digestate and the bureaucratic delays were swept away in April 2010. Regulation in this area is still more complex than the Sludge (Use In Agriculture) Regulations 1989, but there has been huge improvement.

For AD to be viable financially, a critical mass of feedstock is required, and co-digestion could make this available within a reasonable distance. Co-digesting with sewage sludge would use existing assets at sites that already have truck traffic and grid electricity connections. It seems that a bit of courage (but not genius) is needed to cut through the complexity that has been layered on AD in the UK and thereby unlock its potential.

Dr Tim Evans on behalf of BioResources and Environment Groups

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