How AD can wet the appetite of local authorities

Anaerobic digestion can deliver much more than a waste solution to councils. Mark Richmond outlines how waste managers can play a role in realising the wider benefits of this technology

The use of anaerobic digestion as a means of treating waste materials is nothing new in the UK. There are currently around 500 digesters located on some 200 sites, mainly operating within the wastewater industry.

The increased uptake of the technology within the municipal waste treatment sector is also well established with over 25 digesters processing organic waste as authorities collectively work towards national targets to divert biodegradable waste from landfill.

To date, these targets have been the principal driver behind the development of AD in the municipal waste sector although an increasing range of sustainable energy considerations are encouraging local authorities to view AD as more than just a waste treatment option.

At the national level, the UK is bound by a variety of targets to produce energy from renewable sources. The Renewable Energy Directive stipulates that 15% of the nation's electricity should be produced through renewable sources by 2020, including a target of 10% for the production of transport fuels from renewable sources.

In the more immediate future, the Renewables Transport Fuels Obligation aims to see 5% of transport fuels produced from renewable sources by 2014. AD is well recognised as being a key constituent of the technology mix in working towards these targets and it has been estimated that fulfilling the national potential for AD could produce 16% of road fuels or 1% of current electricity demand in the UK.

The ability for AD to contribute to these targets lies not in the technology itself but in the waste that it processes. With around 7M tonnes of food waste arising within the municipal stream each year, local authorities are already exploring opportunities to tap into this energy resource.

This was recently illustrated in a study undertaken for three Teesside authorities funded by the North East Regional Efficiency Improvement Partnership (REIP).

Hartlepool, Middlesbrough and Stockton councils, working through the Centre for Process Innovation, commissioned WSP Group to undertake a feasibility assessment for an AD facility within the authorities' area.

With landfill diversion targets covered by an existing joint residual waste disposal contract, the study focused on potential biogas outputs that could be derived from food waste feedstock collected.

This included using the resulting energy to generate electricity and heat, to inject into the National Grid and to produce road fuel for use in the authorities' refuse and recycling collection fleet.

The study estimated that some 30,000 tonnes of food waste could be captured from a combination of source segregated household food waste collections and from the local commercial and agricultural waste streams to generate 4.5M cubic metres of biomethane per year.

This may appear small in a nation that consumes 95B cubic metres of methane gas annually although the opportunity this presents to the authorities involved is substantial. The outputs could be used to generate around 1.5MW of power in an area with a high industrial load demand, or alternatively, to displace the 1.9M litres of diesel consumed by the authorities' vehicle fleet annually - a move that could deliver savings of up to 48% on fuel costs alone.

At face value these figures present a compelling case for the development of an AD facility in the Teesside area, although evaluating the findings at a strategic level provides further evidence of the opportunity for local authorities to contribute towards the wider sustainability agenda.

As organisations with property estates that create energy demand, and as operators of large vehicle fleets, local authorities are uniquely placed to have direct access to a renewable resource that enables these energy requirements to be met in a sustainable manner.

The study undertaken for Hartlepool, Middlesbrough and Stockton has led the way in demonstrating this point and has illustrated how local authorities can respond to these energy drivers alongside waste management targets.

The opportunity exists for other local authorities not investigating AD to examine how the food waste resource they manage could be better utilised in this wider sustainability context.

It is clear that making progress towards energy targets relies in part on waste managers to fully understand the role they play in realising the energy potential of the food waste stream through technologies such as AD. This requires waste to be viewed not as an isolated issue but as an authority function that can support other issues such as energy supply and fuel procurement.

A proactive approach from local authority waste managers to colleagues working in procurement and fleet management highlighting the opportunity for AD can only be viewed as a positive first step. The Teesside study also suggests that waste managers may need to extend this dialogue to neighbouring authorities to achieve a scale that is technically and financially feasible.

So, what next for Hartlepool, Middlesbrough and Stockton? As the potential for a facility has been established, work will begin to identify potential project partners and consider many of the challenges that accompany the development of the facility such as finance and planning.

The next step for other local authorities is for waste managers to reflect on these wider sustainability drivers and to explore opportunities for technologies such as AD to deliver much more than a waste solution.

Mark Richmond is a principal consultant at WSP Group

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