The UK water sector looks set to benefit from plans to significantly increase renewable energy generation via anaerobic digestion set out in the Government’s new Anaerobic Digestion Strategy and Action Plan.

The Action Plan sets out in detail the actions needed to bring about an increase in energy from waste through anaerobic digestion(AD). AD has a number of key advantages over other renewable energy technologies. Unlike wind, tidal and solar power, the energy is generated constantly, and can be stored in the grid (in the form of gas). The construction of AD facilities can be comparatively swift, and compared to some other waste management technologies can be relatively inexpensive. The inputs and outputs of the technology are flexible, meaning that the plants can be designed to meet local requirements for feedstock or outputs, while remaining connected.

Key actions in the strategy and action plan include:

• guidance on the cost and benefits of AD to developers and local authorities
• evidence on the value of digestates
• developing skills and training for AD operators
• highlighting ‘best practice’ projects that deliver community benefits

The Government has pointed out that the AD Strategy and Action Plan is not a comprehensive road map – instead it reflects the level of evidence and information currently available, and the relative immaturity of the AD industry in England.

However, AD itself is not a new technology, and has been widely applied in the UK for the treatment of sewage sludge for over 100 years. The government’s plans for growth in the use of anaerobic digestion to increase renewable energy generation has significant implications for the UK water sector.

Water sector could significantly increase AD capacity

The waste water industry already has capacity in place and commonly uses AD technology to treat sewage sludge and, increasingly to generate renewable energy.

AD is one of the most important methods for treating sewage sludge and roughly two thirds of the country’s sludge is already treated in this way. The water industry has a well established infrastructure of AD plants and extensive knowledge of the technology and its operation. In 2008, of 1.6 Mt of sewage sludge produced annually by the industry, 66% was treated by AD and 60% of the biogas produced by this process was used to generate renewable heat and power using a CHP engine.

Current water industry installed capacity in this area is estimated at 115 megawatts (up to 1 TWh). This contributes approximately 90% of the energy currently produced from AD in the UK. Around 75% of the 1.1 Mt of sewage sludge produced in England and Wales is used on agricultural land – five of the water companies are over 90% dependent on this recovery route for treated sewage sludge.

The co-digestion of food waste in large sludge treatment plants is a key area for potential expansion, particularly as many of the plants are conveniently located by urban centres. Around 16 million tonnes (Mt) of post-farm gate food and drink waste arises annually in the UK.

Similar potential also exists in the estimated 90 million tonnes of farm manures and slurries generated each year. The report says AD could be used to capture methane from stored slurries and manures, and also to stabilize and treat these materials.

At the request of water industry regulator Ofwat, the Office of Fair Trading (OFT) recently launched a market study into the market for the treatment of organic waste. The study is looking at organic waste arising from sewerage businesses (sewage sludge) and from municipal, commercial and industrial sources (including agricultural sources). The OFT report is due to be finalised in July 2011.

AD plants set to more than double

Although AD is widely used in the treatment of sewage sludge, a wider AD industry treating manures, purpose-grown crops or wastes has been slow to establish in the UK. There are currently (April 2011) 54 operational AD facilities in the UK (32 on-farm and 22 off-farm), excluding sludge treatment facilities. Biogas is being used in various ways, most commonly for CHP generation or in a gas boiler for heat generation; however there are also two facilities that will inject biomethane into the gas grid. Currently around 50 additional plants have obtained planning consent, with a total additional capacity of around 70 Mwe, with a further tranche of plants now in the process of obtaining planning permission.

Future potential for significant growth

At the moment the Government say it is difficult to use the planned capacity data to accurately predict the actual level of capacity that will eventually become available. However, with Government keen to see a “substantial increase in the deployment of AD” it looks as if the UK is set for significant growth.

Beyond the UK, AD is widely adopted throughout the world, from large-scale municipal plants in France and Italy, thousands of farm-based plants in Germany, farm-based food waste plants incorporating crop feedstocks in Denmark and Sweden, through to many hundreds of thousands of micro-digesters in South East Asia.

Based on current information available, the Government say the forecast potential for AD deployment for electricity could reach between 3–5 TWh by 2020. To help the development of AD capacity, the Government has agreed that WRAP will set up a new loan fund to help stimulate investment in additional AD infrastructure.

A total of £10m over 4 years will be made available to provide debt finance to stimulate investment in additional AD capacity. The focus and criteria of the fund is still being developed and a more detailed announcement will be made in due course.