Sustainable solution reaps what it sows

Biogen's farm-based application of anaerobic digestion puts food waste to good use and closes the loop by putting back what it gets out. Maxine Perella reports

When it comes to low-carbon technologies for waste recovery, anaerobic digestion (AD) is right up there. The Government is keen to encourage its adoption, and for those local authorities forging ahead with food waste collections and looking to deal with their organics fraction in a cost-effective way, AD might well fit the bill.

One impressive AD facility has been operating in Bedfordshire for the past two years and received the royal thumbs-up when HRH The Princess Royal paid it a visit last Autumn to officially open the plant. Based on 5,500 acres of farmland in Milton Ernest, Biogen's Twinwoods model is a closed loop system as it processes pig slurry on-site and the bio-fertiliser produced is pumped back onto 1,500 acres of land for growing arable crops.

While this is primarily a farm-based application of AD, the plant is also processing food waste right along the food chain, from commercial and industrial outlets through to source-segregated household collections. The food, which can be delivered packaged or unpackaged, is mixed with the pig slurry fed through underground pipelines from a pig finishing unit sited nearby.

The food waste makes up the majority of the mix - the plant has an annual capacity of 42,000tpa and about 70% of this is food - but the pig slurry acts as a stabiliser for the substrate, making the digestion process more robust. Besides the bio-fertiliser, the biogas produced powers a combined heat & power unit and the electricity generated is sold on to the National Grid. The plant can produce 1MW an hour, enough to power 1,000 homes.

Andrew Needham, who heads up Biogen, has his roots in farming. Biogen is a division of the Bedfordia Group and its sister company is Bedfordia Farms, a family-owned farming business. Needham says the Twinwoods plant was developed primarily to make the farming business more sustainable.

"This plant was set up in 2005 and it was the first plant in England to be fully integrated into a farming operation. We have a 1,100 sow breeding unit on our site, from which we grow about 22,000 pigs a year. We needed to invest in our livestock operation and part of that was establishing a new pig finishing unit which would produce about 12,500m3 of slurry a year. So we looked at how we could add value to this in an environmentally-responsible way, and anaerobic digestion was the answer."

LATS makes it commercially viable
However, Needham saw an opportunity to put forward AD as a proper business case when he realised certain drivers in the waste industry such as LATS and the Renewables Obligation were pushing for the recovery of waste through carbon-conscious methods.

"AD comes with the best environmental footprint and we have got a very flexible system in terms of what we can handle - we can deal with several different types of food waste. We see that an AD plant works very much as providing a solution for organic waste, whether it comes from the commercial, retail or municipal sector," he explains.

Council trials are leading the way
Biogen is currently receiving source-segregated food waste from five local authorities, two of which - Bedfordshire County Council and Luton Borough Council - are involved with WRAP's food waste trials. Needham estimates about a fifth of the food waste received is coming through this channel and says volumes are "increasing substantially". He adds that the company is looking to work with more councils going forward - it exhibited at LARAC's conference towards the end of last year where its presence generated a lot of interest among delegates.

"We've got a planning application going in imminently for another plant in the Midlands and we have some other sites lined up as well. We are looking to roll out our model through second-generation plants that will incorporate some pretty radical changes in terms of their design, and build a number of plants across the country."

He adds: "We're looking to replicate the model on other farms, that's where it works really well for a closed loop system. It could in theory also be linked to food manufacturing sites, but you need quite a bit of available land for this. We are also looking at using the electricity and heat generated locally on future sites - so it goes into an end-user direct, rather than the National Grid."

Biogen's growth plans for AD are ambitious - the company is looking to build another 100 plants across the country over a ten-year period. But, as Needham points out, with the technology still in its infancy in the UK and Biogen's already-established operational expertise, the company is in a great position to put its experience into further practice.

For now, Needham is busy working on a digestate standard for AD due out in the Summer. Biogen is part of the pilot scheme for this, along with other key stakeholders including WRAP, the Environment Agency, and the Renewable Energy Association - where Needham also sits as vice chair.

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