GETTING more energy from the feedstock they are using is now a core driver for operators of anaerobic digestion (AD) systems in Northern Ireland. It’s an approach that makes economic sense while also helping to ensure that the overall objective of producing green energy is secured in ways that make best use of the raw materials utilised.
The good news, however, is that this objective can be achieved as the science at the very heart of anaerobic digestion continues to unveil new management options that have been specifically designed to ‘ramp up’ AD efficiency levels.
A case in point is Eglinton farmer Donald Montgomery. He has been successfully managing a 500kw AD plant since 2016. The business complements the family’s dairy farm and extensive agri contracting operations. All of the electricity produced by the plant goes to the National Grid.
The feedstock for the plant comprises a mix of grass silage, wholecrop, cattle slurry and maize meal. Most of these inputs are home produced with the digestate produced by the system representing a valuable fertiliser for the land that is dedicated to the AD business.
“The land is managed to ensure that we can achieve the best possible crop yields,” David explained.
“The grass land area is regularly re-seeded and we build in crop rotations that ensure soil quality is always being improved.
“We take four crops of grass silage annually.”
From the outset Donald was fully aware that his AD plant is similar in nature to a cow’s rumen. As a consequence, feedstock quality must be maintained at all times. He added: “We have managed to keep the biology of the plant right at all times. This is reflected in the fact that our plant efficiency levels have consistently averaged 95 per cent from the very outset.”
But despite every effort that can be made, David is also aware that factors – such as the weather – can have a significant impact on the quality of the feedstock that is available to his AD operation.
“We ran into this very problem midway through 2017. Analysis of the grass silage being fed into the system at that time confirmed that its energy content was significantly below what we would have been using up to that point.
“I had no option but to increase the silage feed-in rate in order to compensate for this factor. This immediately added significantly to the costs incurred by the business.”
At that stage Donald was made aware of the research work that Alltech had carried out in developing practical solutions to improve AD efficiency levels.
“I was already very conscious of the work Alltech had been doing in developing nutritional solutions for dairy and beef cattle, which are centred on improving rumen efficiency,” he said.
“So, when I was approached to trial the company’s new ‘Digest P3’ biogas solution, there was no hesitation on my part to come on board.”
Alltech’s Barry Purcell was a recent visitor to the Montgomery farm.
“Digest P3 can have a benefical impact on your AD plant in one of two ways,” he said.
“The enzyme complex helps the microbes produce more gas from an existing feedstock or it can support an AD plant to produce a higher than would be expected quantity of gas from a lower quality feedstock if the conditions within the digester are changed on a gradual basis.
“In either case, improved fibre digestion is at the heart of the process.”
Digest P3 is now being used by AD operators throughout Europe.
The unique enzyme complex that is Digest P3 was cultured through a process called solid state fermentation (SSF). Alltech has pioneered the production of solid state fermentation technologies for the animal feed industry. Eight years of collaborative research bet-ween Alltech’s bioscience centres in Dunboyne, Republic of Ireland, and Kentucky, USA, led to a $40 million state-of-the-art production facility in Serdan, Mexico. Digest P3 is produced in this facility, where a selected strain of Trichoderma longibrachiatum is used to create the specific enzyme complex. Through this process multiple enzymes can be produced at once instead of creating just a single substrate enzyme.
The product works with methane-generating microflora to help break down feedstock components previously inaccessible through digestion.
This enhanced feed breakdown allows for more readily available energy and protein for the microflora, resulting in additional biogas volumes from the same amount of feed input.
Digest P3 also allows for flexibility in feedstock formulation through the inclusion of byproducts and alternative raw materials.
Alltech has undertaken a major research trial with Harper Adams University to identify optimum per-formance-enhancing additives. The trial was run utilising Digest P3 in commercial plants across Europe. In the trial, Digest P3’s additional feed breakdown led to increased biogas production, reduced feed costs, reduced power consumption and uplifts in operating profit. The
results have been replicated on the back of the results achieved by Donald Montgomery with the product.
He explained: “Adding the Digest P3 couldn’t have been simpler. It was simply a case of mixing two 500g biodegradable bags of the product per day with the feedstock. The static mixer wagon, which treats all feedstock prior to its addition to the digester, ensured that the Digest P3 enzyme complex was mixed thoroughly at all times.
“I can confirm that the addition of the Digest P3 led to a daily reduction in silage usage of three tonnes, while maintaining electricity generation at the required output levels. This represented a saving of £90 per day.”