Eco system to save energy

Steel city: Propser De Mulder's ReFood UK anaerobic digestion plant in Doncaster
Steel city: Propser De Mulder's ReFood UK anaerobic digestion plant in Doncaster
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pioneering technology that could prevent tens of thousands of tonnes of from being dumped into landfill sites by turning it into a valuable source of energy and nutrients could soon be appearing on sites across the country, thanks to Doncaster-based Prosper De Mulder.

The revolutionary clean and green system uses anerobic digestion, or AD, and will act as a shining example when it comes to persuading doubtful residents that they have nothing to lose and everything to gain from having an AD plant in their area.

You just have to look at the response from people living near to the Ings Road factory when they visited the site months after Prosper De Mulder had won permission to build the new plant. The one question on their lips was when the plant was going to be built and they were stunned to find out it hadn’t just been built but was already up and running.

“They thought there would be smells and noise. They can’t believe that it is here,” says Prosper De Mulder’s commercial director, Philip Simpson.

The firm’s new ReFood operation is a showcase development, which the company hopes to repeat across Britain, with each plant serving businesses within a 50 mile radius - about the economic limit for the concept.

“We could have gone for a lower cost design and a cheaper operation, but this is a showcase and any other units we build will be at least as good as this and, I would like to think, better. We want to improve the environment, not just make money out of it,” says Mr Simpson

The theory behind ReFood’s anaerobic digester is simple. You pour food waste into a container with some bugs inside and no air.

The bugs eat the waste, producing bio-gas, liquid fertiliser and more bugs – and off you go again.

The reality is more complex. First of all the logistics involved in collecting the waste is complex, but nothing Prosper De Mulder, which already uses an electronic scheduling, routing and tracking system to coordinate the owner drivers who move 450 of its trailers around the country, picking up waste to be processed by its other businesses.

The firm has invested in 100 dedicated ReFood collection vehicles which collect bins of food products that are being disposed of by business ranging from large supermarkets to small cafes because they haven’t been used, are unsaleable or left over.

In their place it leaves empty bins that have been cleaned and sanitised at its Doncaster plant.

Once the waste arrives at the plant it has to be checked to ensure there are no contaminants, separated from any plastic, cardboard or paper packaging using innovative depacking technology, blended to form a puree and then mixed with other organic waste to ensure the mixture has the right combination of nutrients the bugs need, before it is pasteurised.

Meanwhile, the wheelie bins that held the waste are comprehensively cleaned – and so is the truck that brought them.

Digestion in the bioreactor takes about a month and the biogas has to be cleaned before being used to fuel two 60 litre, V20 engines that are the most efficient generators on the market and produce electricity for the Doncaster plant and the National Grid a well as heat which is used in the plant.

The fertiliser, rich in nitrates, phosphates and potassium is delivered to local farms, where it is stored until it is needed.