LAWR

March 2014 Local Authority Waste & Recycling 17 ENERGY RECOVERY n Europe, anaerobic digesters are normally perceived to be sizeable installations, but by far the largest number of digesters in the world are small, using locally available feedstocks, and providing health benefits, fertiliser and energy to rural communities. But can such small local digesters be translated to a UK situation, where the drivers are completely different and rules more stringent? James Murcott, who has been building successful small farm digesters in the UK for 40 years believes they can. He says: "Small digesters fed on locally available feedstocks can offer renewable energy, excellent fertiliser production and a cost-effective organics treatment solution in many situations, both urban and rural." When Murcott moved off- grid a few years ago and wanted an AD system to suit his situation, he found that there were none on the market, so designed a range of 'micro' anaerobic digesters, ranging in size from .2m3 to 20m3, a number of which have been installed in urban situations, farms and smallholdings. Rokiah Yaman from London's Local Energy ADventure Partnership (LEAP) is enthusiastic about their use in an urban environment. He says: "Our vision is to see networks of cost- effective urban micro-AD systems running largely on local food and non-woody garden waste, such as lawn mowings. Such networks would provide low-cost, low-impact waste treatment systems, a closed-loop cycle that could support communities with education, employment and training opportunities, renewable energy and fertiliser for local food growing and urban greening projects. Businesses, schools, universities, social housing flats, allotments and even individual households could all host a digester and be part of the network." With the support of a number of visionaries, including WRAP and Camden Council, LEAP are currently setting up a number of micro-AD plants in Camden, with the first operational unit at Camley Street Natural Park, located a few minutes' walk from London's bustling King's Cross. Food waste for the micro-AD plant is collected from local businesses using specially-adapted bicycles. LEAP plan to use the digestate fertiliser in community growing schemes, small- scale growing trials, hydroponics, aquaponics, greenhouses and vertical growing trials in order to demonstrate its use in a wide variety of applications, particularly those suitable for urban Anaerobic digestion in the city Angie Bywater is a project manager at Methanogen. Working for over a decade within the anaerobic digestion (AD) industry, Bywater has a specific interest in micro and small-scale farm AD. She will discuss the challenges of dealing with digestate in an urban setting on Day One's Energy Recovery afternoon session (13.10pm-14.10pm). Here is a sneak peak about what to expect on 1 April. I situations. They plan to use the biogas in a number of ways, including polytunnel heating, trialling micro-biomethane upgrading and micro-combined heat and power (CHP). Almost 15m tonnes of the UK's food ends up in landfill every year, with London's food waste alone representing 6.3m tonnes of greenhouse gases. There are huge political, economic and environmental pressures to remove these organic materials from landfill and to reduce waste, with the London Plan specifically encouraging a proportion of waste treatment within the city itself. However, despite proximity to concentrated sources of feedstocks and significant energy demands, the construction of large AD systems in urban areas is extremely problematic due to high costs, public objection, lack of land space and the extra traffic involved in transporting feedstocks into the plant and the digestate fertiliser back to land. The profitability of such large plants is sensitive to transport costs, waste volumes, gate fees and renewable energy incentives. If, as required by the waste hierarchy, these organic waste volumes are reduced, such plants can quickly become unprofitable, with geographically co-located plants vying for increasingly reduced food waste volumes. I have been operating a small anaerobic digester in my urban back garden for more than two years, recycling around two tonnes of local food waste into fertiliser used for food growing, with the biogas being used for cooking and greenhouse heating. A micro-digester could also work well in rural areas, reducing food waste miles and providing fertiliser to farmers. Why transport small quantities of dispersed food waste many miles, when it could be used beneficially at a local level? I believe that small and micro-AD systems should be encouraged and incentivised, not only for renewable energy production, but for their larger greenhouse gas reduction and pollution mitigation potential. At any scale, anaerobic digestion is central to a sustainable food production system in a circular economy, and is far more than just a renewable energy technology.

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