Keston Williams, technical director at Barfoots, says anaerobic digestion has worked extremely well due to the firm's green waste issue
Barfoots has been a keen advocate of anaerobic digestion at its glasshouses and fields in Selsey, West Sussex. We put technical director, Keston Williams, under the spotlight to find out how and why the supplier of supermarkets and national restaurant chains has gone down this route of sustainable agriculture
When did Barfoots first consider anaerobic digestion as a viable option?
Keston Williams (KW): Barfoots first realised it might be an option during a work trip to Germany in 2008. Anaerobic digestion was being quickly adopted and it looked like it might solve our problem of dealing with large amounts of green waste. Sweetcorn creates a great deal of green waste when the ends of the cob are cut off and the husk is removed, and there weren’t enough cattle in the local area to take the volume of green waste we were producing. We considered composting and creating our own beef herd, but we soon realised that having one big cow (an anaerobic digestion plant) was the right investment for us.
What was the most challenging aspect of establishing the anaerobic digester?
KW: The recession in 2009. No one wanted to lend cash to any business and the economy seemed to be in free fall. Investing £4.5 million in what was at the time relatively new technology would have been a bit of a risk. In the end, [company founder] Peter Barfoot decided to fund it through the business, together with a small grant from SEEDA, and we started the development process.
Compared with initial expectations, how does the every-day working model of anaerobic digestion stand up?
KW: We designed the anaerobic digestion plant to produce 1.1 megawatts (MW) of output from two primary digesters and a secondary storage tank. By playing around with the feed sources and the biology of the plant we quickly realised we were producing more gas than it was originally designed to do. We therefore invested in a second combine heat and power plant (CHP) that produced a further 1.2MW, allowing us to produce a maximum output of 2.3MW.
This increased output has made a big difference to payback period by effectively doubling the original planned output. The everyday working aspect of the designed plant is far more complicated than other green energy forms. It’s not like a solar that requires a clean every couple of years or a wind turbine that needs a bit of grease every few months; our designed plant is like a baby that needs constant feeding, care and attention 365 day a year.
Is there anything you would do differently, if you did it again?
KW: The anaerobic digestion plant that was specifically designed for us had a great deal of extra tolerance built into it. Essentially, it was over engineered and the output was underestimated. We’ve also found that the secondary tank adds very little to the overall gas generation capacity of the site and therefore we would just stick with two primary tanks and not build the secondary. If we had known that the anaerobic digestion plant was capable of 2.3MW, we would have built this into the plan at the start, rather than having to upgrade and retrofit additional capacity after the build.
Five years on, how is anaerobic digestion helping your business?
KW: We have a completely sustainable energy supply, and we use a third of what we produce within our organisation and export the other two thirds to the grid. We have energy security for the foreseeable future and will not suffer if the energy prices suddenly shoot up. The waste problem we once had has now dissipated and there are no longer tractors driving on the local roads moving green waste around – in fact, more than 5,000 tractor journeys have been eliminated in this process. The digestate produced by the anaerobic digestion plant also provides enough nutrients to allow us to grow all our crops at Sefter Farm without the need of artificial fertilisers.
The image of anaerobic digestion in the UK and Europe has changed greatly. How has this shift affected Barfoots?
KW: The UK still trails massively behind other European countries when it comes to anaerobic digestion, particularly Germany. The granting of planning permission for new anaerobic digestion plants continues to be difficult, but the biggest challenge right now is the price of energy. Whilst oil prices remain very low, together with low gas prices, producing electricity remains relatively low cost. Low energy pricing does not help the anaerobic digestion industry, which currently relies on subsidies through Feed In Tariff (FIT) or Renewable Obligation Certification (ROCs) to make them viable.
What do you think the future holds for anaerobic digestion in the UK?
KW: Whilst relatively low energy prices remain, the anaerobic digestion industry will live or die with government policy and the subsidies through FIT or ROCs. If energy prices increase significantly and anaerobic digestion has an opportunity to stand on its own, then it will have an exciting future.
The Barfoots team are keeping a close eye on technological advances in anaerobic digestion that might increase gas production further, but this is likely to be some way off commercial application. Making better use of the digestate is something else we are also investigating and there may be other opportunities to produce products that can add value.
What advice would you give any fresh produce companies looking into anaerobic digestion?
KW: Anaerobic digestion has worked extremely well for us, but it was due to our green waste problem that the project became a success. If you have a feedstock that is high in calorific value and low in dry matter with plenty of fibre, then you have an opportunity to produce a good gas output. Also, don’t forget what goes in must come out; digestate is expensive to transport and can be costly to spread. We are lucky that our farm surrounds our anaerobic digestion plant, allowing us to efficiently move and spread digestate, so sighting of the plant is critical in your planning.
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