SLURRY DRIVES BIOGAS PLANT OUTPUT AND
FARM’S GREENER FUTURE
With energy prices soaring, the ability to dispose of pig slurry by turning it into electricity is attractive enough. But when the by-product of the power generation can also cut the arable land nitrogen bill, any large-scale farming operation would sit up and take notice.
This is exactly the reality for Bedfordia Farms based at Milton Ernest near Bedford. The family owned farming business integrates an 1100 sow, 4,800 finisher place pig unit with 2000 hectares of arable land and bang in the middle is a state-of-the art, biogas plant run by sister company Biogen.
Biogen takes pig slurry and material everyone throws away – particularly waste from the UK food chain – and uses it as fuel to make renewable energy. Each year, around 12,000 tonnes of slurry travels effortlessly from the Twinwoods pig unit via a 250m underground pipeline straight into the biogas facility. Up to 30,000 tonnes of food chain waste is mixed with it to fuel the digestion process, producing methane which in turn is used to power a combined heat and power generator that produces enough electricity for the pig unit and up to 1000 homes.
“Our process is a unique, farm-based application of an established eco-technology called anaerobic digestion,” explains Biogen operations manager Phil Moffat. “The process uses bacteria in a sealed chamber to break down the slurry and food waste and produce a methane-rich biogas and high nutrient bio-fertiliser.
“It really is a win:win:win situation: it’s a green solution for the disposal of pig slurry and food chain waste in a sealed process that reduces pollution. It’s also a bonus for the arable farming operation because it produces a valuable liquid bio-fertiliser that delivers significant environmental and financial cost savings. Finally, we are converting waste into renewable energy, which helps to reduce greenhouse gases and carbon emissions.”
The slurry from the Bedfordia pig farming operation forms the basis of the biogas plant’s raw material intake and is essential for achieving the porridge-like consistency ideal for the anaerobic digestion that produces the methane. But it’s the food waste, with its higher energy content, that boosts the methane yield.
“We are able to accept almost any form of food waste – liquids, sludges or solids – and we can take both packaged and unpackaged material,” Phil Moffat says. “When you consider the UK produces up to 30 million tonnes of food waste annually – most of which goes into landfill – biogas plants offer a far more cost-effective and environmentally-friendly alternative.”
Ensuring the pig slurry remains fluid and flows well into the plant is also a crucial part of the process. Keeping slurry moving is a familiar problem for pig producers and reducing crusting in lagoons and tanks is vital for effective agitation and pumping.
“It’s important that the slurry stays fluid so that we can pump it easily to the biogas plant,” points out Bedfordia livestock manager Richard Smith. “In the past we’ve tried various slurry additives to keep things moving, including enzymes, but none have really helped – particularly in terms of breaking down our surface crusts. However, about 18 months ago at the invitation of East Riding Farm Services, Phil and I visited a pig unit in Denmark that claimed to have cracked all their slurry handling problems.
“The unit manager explained that their success came from mixing in a small amount of a natural, mineral-based powder called Viscolite. Initially, we were pretty sceptical, but intrigued enough to give the product a try – particularly as it is considerably cheaper than many enzyme additives we have tried. And I have to say we’ve been very pleasantly surprised by the results.
“Since introducing the powder, slurry agitation in the tanks has become so much easier. In the past, when we’ve had tank agitator breakdowns and slurry solidifying as a result, it has taken us a week to get it moving. But when we had a similar problem recently, we were able to agitate again within half a day.
“Since introducing Viscolite I can honestly say that in 40 years of working with pigs this is the easiest we’ve ever moved slurry. Now we can pump out 200 tonnes in as little as 1¼ hours with very little solid material left over. The residual sludge is only ankle deep when we have finished pumping,” Richard Smith says.
Viscolite is new to the UK. National distributor C&H Nutrition points out that it breaks down hard crusts on the surface of slurry. As well as promoting a more fluid mix of sediment and floating layers in the storage tank – cutting the time and diesel costs of agitation, pumping and spreading – the natural additive can also boost slurry nitrogen content, and reduce manure and dirty water odour. It can be easily added to the slurry, either via the reception pit, channels or slats, or directly into the lagoon or storage tower.
Bedfordia are now using the natural powdered additive both at the pig unit – simply sprinkled between the floor slats at 20g/m3 – and in the biogas plant, again to improve tank agitation with similar results, as Phil Moffat explains.
“We recently needed to empty a 36 metre, 5000 tonne tank with two mixers in it for maintenance. I didn’t think we would get the material out, but it emptied easily to ankle deep depth which is amazing,” he says.
The liquid, nitrogen-rich bio-fertiliser left at the end of the biogas generating process also handles well, Phil Moffat says. The plant produces around 30,000 tonnes a year of this valuable by-product and it is used as a soil conditioner on 600 hectares of milling wheat.
The exact nutrient make-up of the fertiliser varies with the nature of the food waste used, but typically delivers 4-5kg/m3 of nitrogen plus lesser quantities of phosphate, potash and magnesium. When required, Bedfordia can easily spread 1000 tonnes a day.
“The plant incorporates final storage tanks for the fertiliser so that several months of production can be stocked and fed onto the fields at the right time for the crops. It also means we don’t have to buy-in fossil-fuel based nitrogen fertiliser that has escalated in price so dramatically because of the oil price rise,” Phil Moffat says.
Bedfordia Farms is clearly demonstrating that exemplary green credentials do not necessarily have to come at the expense of highly cost-efficient agricultural production.