Anaerobic digestion (AD) has had a good press recently. The Government Waste Strategy published by Defra two years ago mentioned it over 20 times. BERR subsequently said of AD that a “significant growth in the use of AD in the UK would be in the national interest”.
Such endorsement from Government is unusual, but the reasons are clear. AD is one of a number of technologies that sits across the waste and energy sectors, at a time when the Government is trying to hit stretch targets on the diversion of organic waste from landfill, and the generation of renewable energy. Better still, it does it in a way that is very environmentally friendly.
James Astor is managing director of Agrivert Biogas. The Chipping-Norton-based firm has a number of AD projects in development
AD had not until recently offered commercial returns in the UK outside of the water industry. However, the award of “double ROCs”, confirmed in April 2009, has tipped many AD business plans into the black, and other financial support in terms of direct grants and the introduction of a renewable heat tariff will further help.
However, developing AD to process the UK's household and commercial waste still poses challenges which need to be thought through by potential operators. The credit crunch has hit the willingness and ability of the banks to lend money, even against projects with sound business plans. Securing long term municipal contracts can be time consuming and costly, and many procurement processes are concluded with no award made. Grid connections can be expensive, even where there is sufficient surplus capacity in the network to take your power. Planning is also expensive, and is not assured. The quantity of regulation can be daunting.
Assuming these issues have all been successfully negotiated, operational challenges remain. Whilst AD technology has been long established, it has been mostly used in the treatment of relatively homogenous organic feed stocks. Household kitchen waste, retailer waste and other commercial wastes are neither homogenous nor entirely organic. De-contaminating feed stocks at the front end, and balancing the feed stocks in a way that support the microbiology of the digesters is therefore critical.
An AD plant also produces digestate. In order to keep receiving waste at the front end, a secure outlet for this product must also be found. Whilst digestate is valued by farmers, it is also bulky. Even when dewatered, the logistics of digestate disposal, whether to land or via some other route, require careful planning and budgeting. The agricultural outlet contains many idiosyncratic sensitivities and it is also covered by regulation when spread to land (The Nitrate Directive and PAS110/Quality Protocol or WMX7).
The good news is that despite all these challenges, there are are many AD plants now in planning. The ones that subsequently perform well will have carefully thought through all of these different issues, and mitigated potential risks through careful planning and plant design.
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