Processing food waste using anaerobic digestion technology is not necessarily as expensive in relative terms as some councils may think, consultancy Eunomia has claimed.Speaking at the AD In the City event held in the UK by BiogenGreenfinch last month, senior consultant, Dr Adrian Gibbs, said that using AD to process food waste collected separately could work out cheaper than processing commingled food and green waste together in an in vessel composting plant.
Dr Gibbs explained that a report by Eunomia had found that sending food waste to AD and green waste to windrow composting cost UK councils £9.50 in gate fees per household per year, whereas sending commingled green and food waste to IVC cost £10.80 per household. He also said that just collecting food waste alone and sending it to AD cost £5.50 per household over the same period.
Dr Gibbs admitted that average gate fees for AD facilities - around £55 per tonne - were higher than IVC - which, he quoted as £45 per tonne, but said that "overall AD is cheaper". He also claimed that separate food waste collections also worked out cheaper than mixed collections and said that the number of local authorities which were implementing separate collections had risen from 11 in 2007 to 54 in 2008.
He told the London borough council officers who attended the event, which was set up to explore ways to introduce more AD capacity in London, that - "AD is better than IVC, it's the way to go and it is the one I would watch."
Anaerobic digestion treats food waste in an oxygen-free environment and produces biogas - which can be converted into energy - and a nutrient rich digestate which can be used on farmland. It also has the potential to provide combined heat and power (CHP).
IVC treats green and/or food waste and sometimes card in an enclosed but oxygenated and aerated environment and produces compost. It does not generate energy.
A number of strengths and weaknesses were highlighted for both separate and mixed collection. The plus side to mixed collections included - only needing to use one vehicle, only one bin required and quick and cheap collections.
However, Dr Gibbs explained that the seasons significantly affected what was collected, with garden waste levels dropping significantly in the winter, meaning that feedstock was inconsistent. He also said that the waste had to be processed in an enclosed environment due to Animal By-Product Regulations and this ups the cost of green waste.
Dr Gibbs also pointed out that green waste and food wastes required different collection frequencies. In addition, not all homes have gardens and collecting green and food waste together prevented councils charging for green waste collection. He claimed that separate AD collection reduced net costs for councils and allowed local authorities to charge for garden waste. He added that there is a large quantity of food waste which could potentially be picked up.
Dr Gibbs said AD had a number of strengths, including -
* Internationally proven technology
* AD has strong government support in the form of ROCs, a Task Group and feed-in tariffs
* It is a carbon positive technology
* Valuable outputs - biogas and digestate - and
* Leaves green waste to go through the cheaper windrow process.
He said AD's only weakness was the lack of facilities in the UK, adding - "AD wins hands-down for organic waste."
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