Weekly collections key to success of AD waste treatment

Anaerobic digestion (AD) can treat food waste economically if supplied by weekly collections, trial results show.

Biocycle’s AD plant in Ludlow, Shropshire, completed its second year of operation in March.

The 5,000-tonne capacity plant began operating in March 2006 as part of the new technologies demonstrator programme run by the Environment Department (DEFRA).

It performed poorly in its first year, generating less than 100 megawatt hours of electricity, which is far short of its 1.2 gigawatt hour capacity (ENDS Report 388, pp 19-20 ). The company - a joint venture between South Shropshire District Council and technology supplier Greenfinch - blamed this on the low level of food waste it received, equivalent to just 5-7% of feedstock.

But the plant’s second year saw a vast improvement. It treated 3,300 tonnes of waste - 95% food - from weekly collections in Ludlow, Somerset, and Newtown in Powys. This generated 800MWh of electricity, 85% of the maximum possible from that volume of waste.

Biocycle could not say how much lower the plant’s greenhouse gas emissions were compared with landfill because the government has yet to publish data on emissions from landfilled food waste.

"The second year was a great improvement after the move from co-mingled kitchen and garden waste collections to dedicated food waste ones," said Michael Chesshire, Greenfinch’s director. "We think we’ve now shown AD is very promising on a practical, economic and greenhouse gas reduction level."

Biocycle has analysed the commercial viability of AD at gate fees of £40-60 per tonne of waste. This suggests a merchant facility would be viable at 20,000 tonnes per year capacity. A local authority-run plant, which does not require high profits, could operate successfully at 5,000 tonnes per year.

Biocycle expects to finish its trial as part of the demonstrator programme in September, but will continue operating on a not-for-profit basis afterwards. It has just started taking commercial food waste from 60 Ludlow businesses.

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