Scottish Water to build anaerobic digester

By Ryan C. Christiansen
Web exclusive posted Jan. 16, 2009, at 10:01 a.m. CST

Scottish Water Waste Services, a water and waste water services provider based in Dunfermline in Fife, Scotland, plans to build a �7 million ($10.2 million) anaerobic digester at the Deerdykes Composting and Organics Recycling Facility outside of Cumbernauld in North Lanarkshire, Scotland, that will produce biogas from recycled food waste. The biogas will be used to generate electricity and heat for the company, which serves 2.3 million households across 30,000 square miles.

According to Donald MacBrayne, business development manager for Scottish Water, the lead contractor for the project is Henry Boot Construction Ltd., a subsidiary of Henry Boot PLC of Sheffield, U.K., and the main technology provider is Monsal Ltd. in Mansfield, U.K. MacBrayne said two 500-kilowatt-hour generators will produce approximately 6,000 megawatt-hours of electricity and 1.1 megawatts of heat annually.

The Deerdykes facility, which opened in October 2006, currently recycles 40,000 metric tons of organic garden waste each year from households and businesses in North Lanarkshire, Glasgow, East Dunbartonshire, West Dunbartonshire, Argyll and Bute. The waste is turned in the Pod brand of compost and topsoil. During summer months, the plant recycles more than 1,300 metric tons of organic waste each week.

The electricity produced at Deerdykes will be used to power the composting facility as well as neighboring sites in the Westfield Industrial Estate. Surplus power may be sold to National Grid, pending an agreement. Heat produced by the plant might also be provided to local homes and businesses. The effluent byproduct from the anaerobic digestion process could also be sold as a liquid fertilizer.

"We've been looking at food waste digestion since 2002 when we first learned of the experience from Denmark when the Danes were doing similar things," MacBrayne said. "We've really been investigating it since then, but we haven't been able to pull in sufficient capital funds up until now. It's very much a project that integrates very well with what we do on the composting site."

The Deerdykes anaerobic digester and power generation facility is expected to be fully operational by April 2010. MacBrayne said another anaerobic digester is planned for a new composting facility that opened last year in Linwood in Renfrewshire, Scotland. He said a third anaerobic digester is planned for Prestwick in South Ayrshire, Scotland.

Municipal waste authorities in Scotland are required to recycle 40 percent of their waste by 2010; 50 percent by 2013; 60 percent by 2020; and 70 percent by 2025 or they will face fines. The Scottish Government has set targets to use 4 percent of municipal waste to produce energy by 2010, 14 percent by 2013, and 25 percent by 2020. Ultimately, Scotland plans to send only 5 percent of its municipal waste to landfills by 2025. The government said currently, 30 percent of municipal waste in Scotland is being recycled.

MacBrayne said in Scotland, household waste is collected in bins and separated into three basic categories: recyclable garden waste, dry recyclables, and other garbage. He said waste haulers have begun collecting kitchen waste in additional containers. Due to animal byproduct regulations, however, MacBrayne said kitchen waste with animal origins must not be composted in the open air. Therefore, anaerobic digestion can be used to recycle kitchen waste into biogas.