29 October 2010

Anaerobic digestion fuel may run vehicles - Horticulture Week

Pearson revealed at the conference - held last month in Coventry - that the Cheshire-based company, which supplies tomatoes to big retailers like Tesco and Iceland, has already developed the fuel and bought its first vehicle, which it hopes will be up and running by next summer. He said: "We have made the fuel - we are just making sure that it is of a consistent quality."


Pearson revealed that the family business, which has been growing tomatoes for 40 years, aimed to have its own eco-fuelling point for the vans, whose bio-methane-based fuel means that they will be able to avoid congestion charges.

Biomethane is one of many products of the anaerobic digestion plant that Pearson built at the growing site in Alderley Edge, Cheshire, a couple of years ago.

All of the waste material from the nursery is fed into the digester, helping the company to reduce its annual landfill volumes from 2,500 tonnes before its installation four years ago to 200 tonnes in 2009.

His confidence in the commercial potential of the anaerobic digestion plant has led him to set up another company, Anaerobic Digestion, of which he is managing director. He told growers: "The opportunities are huge but I have to be careful I do not rush out and get too excited about it."

He explained that the company manipulated the anaerobic digestion process to get as many products out of it as possible. It has managed, for example, to make its anaerobic digestion plant "close to unique" by enabling it to produce liquid digestate rather than the sludge-like digestate typically produced by most anaerobic digestion systems.

Pearson said: "There is not one like it in the world. We are exceptionally proud of it. Most anaerobic digestion plants have solid digestate but ours is liquid.

At the moment it's got a bit of a green tint, which I am not happy about, but nevertheless in the time since we started (this process) we have become the only system in the world with a liquid digestate.

"Lots of anaerobic digestion plants in the UK have gone bankrupt because they kept to the European model, which does not fit with the UK experience." He told Grower after the conference that the problem with sludge digestate is that there is "too much of it around - but now we have a tangible and useful product".

Pearson has made a deal with the Sports Turf Research Institute, which, from next year will enable its associations to use the whitish-green liquid as a fertiliser. He said: "It has enzymes in it that do not work on our crops but that work very well on grass."

The grower has worked with several universities, including the University of York and the University of Central Lancashire, to get to this stage. "We have done a lot of work on understanding what happens in the plant at different phases and times. I want to try and understand what happens," he said.

Scientists have helped develop a pre-treatment vessel to better break down the organic plant material.

Pearson explained: "Plants have a natural ability to heal themselves.

When you chop them up they try to heal and the whole lot goes solid. So we overcame that with a pre-treatment."

The plant matter is held in the pre-treatment vessel for 24 hours after being physically reduced by a flail. The vessel is heated and agitated to give the enzyme-breakdown process a boost. Pearson said: "It helps to accelerate the process by dealing with typically difficult-to-digest materials."

Scientists have also analysed the bacteria involved in the digestion process to "maximise the reduction time to help get the best output".

Pearson added: "We have now halved our reduction time from 14 days to seven." He told Grower that he was continuing to work with the scientist because he eventually hopes to produce a fertilizer that can be used on his crops - and find an energy-efficient way of extracting water from the plant so that it can be used to irrigate the tomatoes.

By next season Pearson also hopes to use the CO2 produced during the anaerobic digestion process on his crops. The company also continues to use the heat and power created from the biomethane to run and heat its glasshouses.

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