Trevor Lea, long-term supporter and user of AD for 20 years

”With just my son to help me, we need things to be simple, reliable and easy to manage,” he said, describing his 80-cow, 80 hectare (200-acre) dairy farm on the Wales-England border.

A 105cu.m digester was installed in 1989 for £25,000 with 50 per cent grant funding to generate gas and heat using sewage waste, then slurry later.

“I got interested in a local farm gas project and put in a unit to provide hot water and heating for the farmhouse and gas for the Rayburn,” he says.

It was two months after starting the digester on sewage waste that the first commercial heat was produced.

“It was a slow start,” he says. “Sewage waste was just too watery. We mixed in slurry but soon found long fibre (straw over two inches long) formed a mat on the surface and gas production fell.

Minimise grit getting

“We avoid using material from the loose housed yards and try to minimise grit getting in, as it adds wear on the equipment. Slurry is scraped off the yards and is added daily to the digester and some spent liquid piped off. Overall, material will be in the system for 24 to 28 days.

“Gas production is relatively stable but we do have a back-up heater and cooker just in case, as inevitably things may go wrong or the digester needs maintenance.”

So successful has the digester been that a second has been commissioned after buying a second-hand unit at an attractive price.

“Key for us is ease of use. It’s built in the farmyard and we can keep a close eye on what’s happening,” says Mr Lea.

“Aside from the gas, the digested material is a valuable fertiliser. As an organic unit, we’ve not bought fertiliser for 20 years. The material is applied to pasture and quickly disappears. Cows are put out 21 days later with no problem. The thing you do notice is digestate turns everything a dark colour - even clover leaves.”

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