Biogas supplies green power

Nick Chesters, May Gurney's regional M&E manager and general framework manager for Severn Trent Water, examines a biogas-harvesting project that is used to fuel combined heat and power units at three plants

Severn Trent Water and May Gurney have completed an extensive biogas-harvesting project at three sites in Shropshire and Powys. The three wastewater treatment works, at Coalport, Monkmoor and Newtown, all boast newly-refurbished biogas systems that extract gas from sewage and use it as fuel for combined heat and power (CHP) units on site.

Contractor May Gurney, a specialist in biogas optimisation, has completed the work as part of a £4.7M long-term partnership. Not only will it allow the sites to reduce their carbon footprints and produce green energy, but it will also prove highly cost effective as Severn Trent becomes more self-sufficient, saving heavily on external energy suppliers' ever-growing costs.

At Coalport alone, where the project has entered a second phase, the digesters produce an average of 2,640m3/d of biogas. This is enough to power the on-site CHP units, which generate electricity to run the site as well as the heat to operate the boilers and perpetuate the digestion process.

General trend
There is a general trend in the water industry towards sewage treatment works capturing biogas - for a number of reasons. The main driver is, ever-increasingly, stringent government legislation, with its requirements for both the reduction of waste to landfill, and the production of renewable energy.

The government is already aware of anaerobic digestion (AD) as a cost-effective means of harnessing energy from the wastewater treatment process. It can be used to generate heat and power for the plants themselves, but there is also the potential for extra electricity, which can be pushed back into the national grid, generating further income for the water company.

AD at these three Severn Trent sites is by no means a new process - in fact, there has been a digester on site at Newtown for 28 years.

Martin Newey, May Gurney project manager, says: "There is a common misconception outside this industry, born of lack of knowledge, that anaerobic digestion is a new idea. Many end users, such as council procurement departments, may not have realised that companies like us and Severn Trent have been working with this technology for decades, and while some new players from overseas are seizing upon the opportunity to repackage digestion and sell it as something new, we are confident that we are still ahead of the game with our advanced expertise and genuine innovation."

Further efficiencies and economies have been driven into the Severn Trent project thanks to the fact that May Gurney handled the entire design process in-house, from taking the outline design produced by Severn Trent's framework designer, through to completion. The final phases of all works on the Severn Trent sites have been to leave each plant and its surroundings in a cleaner and more presentable state than before.

In line with both companies' commitments to social responsibility, and continuous improvement, an inevitable part of the project was to take into consideration the surrounding environment and local communities.

Alistair Jones, regional manager at Severn Trent Water, is based at Newtown. He says: "There is a public nature trail that runs right past this site, and we have had much interest from walkers who are wondering what the big white gas holder is. We are aware of our responsibility to local residents, and have taken steps to preserve the area with investment in the adjoining stretch of nature trail, and measures to protect and conserve local colonies of geese and endangered great crested newts.

"In fact, in accordance with the law, for the duration of the works on site we had installed a small extra perimeter fence solely to protect such protected species, and in future we are confident we will be providing a cleaner environment not just for them, but for everyone."

Renewable resources
Severn Trent already operates 30 CHP plants across its region, utilising methane gas produced from the sewage treatment process. In 2005, this accounted for 51% of all renewable energy derived from sewage gas in the UK and approximately 1.3% of all renewable energy generated in the UK.

Severn Trent has set itself the target of almost doubling self-generation from renewable resources to 30% of its total energy use by 2013. As a result of the success of the Monkmoor, Newtown and Coalport projects

in 2008, the company is already in advanced talks with May Gurney about a further nine CHP projects to help extend the usage of CHP plants across the region. It also intends to install more water turbines in its dams, generate power from energy crops and wind turbines at appropriate locations.

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