Silage additive from FM BioEnergy boosts AD plant’s feedstock

For on-farm biogas plants using crop-based feedstocks, the quality of the harvesting and ensiling processes can make or break the efficiency of the plant and the anaerobic digestion process for the following year, severely impacting gas output and profit.

Having experienced issues with bought-in silage feedstock outside his control, Nick Cowie of Gloucestershire-based JJ Power now uses a silage additive from FM BioEnergy to ensure that the quality of his feedstock ­– and the performance of his digester – remain high.

Feedstock failure

JJ Power operates a 435 kW biogas plant within a larger 700 ha farming operation, based around a single 2,750m³ digester. The feedstock is a mixture of chicken manure and maize silage, together with some liquid waste from the animal feed industry. However, when Plant Manager Nick Cowie bought in external silage feedstock from an unfamiliar source, the plant soon hit problems; the digester biology became upset, resulting in a drop in gas output.

Seeking a solution

Nick was keen to ensure that his plant never experienced a silage quality issue again. Already a customer of specialist AD consultancy FM BioEnergy, who provide JJ Power with a biological support and trace element supply service, Nick attended the company’s workshop on silage best practice and learned about the science behind biological silage additives.

FM BioEnergy’s product, Silasil Energy XD, seemed to be the obvious solution; particularly as Nick’s own silage was at risk of becoming compromised. “The way that our clamp is arranged means that we have quite a large, open face, which can result in a significant proportion of the silage being exposed to the air before use,” he explains.

Boosting gas output

Tim Elsome, General Manager of FM BioEnergy, explains how the product works: “Silasil Energy XD is a biological additive which contains bacteria that help preserve the crop during storage, reducing aerobic losses. It also reduces losses when removing material from the open front of the clamp by preventing re-heating and thereby increases the amount of gas produced per tonne of crop harvested.”

Tested and certified by the German Agricultural Society (DLG), it is specifically formulated for use on crops destined for anaerobic digestion, boosting the population of beneficial bacteria and supressing the multiplication of problematic species. This means that fermentation occurs more rapidly –clamps made from treated silage can be opened after just two weeks instead of the usual eight – while losses are reduced, and the silage remains fresh.

As well as the benefits to feedstock storage and quality, Tim adds that Silasil Energy XD can also provide an insurance against issues such as poor fermentation: “Poor fermentation, or a build-up of antibiotic-producing moulds, can have severe effects on digester biology. Once the crop is in the clamp, if you haven’t applied an additive you will have to live with that decision for the rest of the season. Given the benefits in terms of quality that it provides, it really does make sense to use it as a standard treatment when harvesting silage for use as AD feedstock.”

The importance of good practice 

For Nick’s part, having experienced biological issues in his digester as a result of poor silage feedstock over which he had no control, he is now convinced of the advantages of using Silasil Energy XD. His plant has suffered no further biological issues and has now been running smoothly for the past two years. “Good practice in clamping, combined with the use of the silage additive, have to be given credit for our smooth operation,” he affirms.

In addition, as it is freeze-dried, the product is extremely easy to use and apply. “It comes with a bottle and mixer jug; you tip in the XD, add water and shake,” says Nick. “You then just pour it into the applicator tank on the machine. It’s that simple and dissolves easily.”

Keeping silage fresh

Because it uses natural bacteria, Silasil Energy XD is both operator and environmentally friendly. Furthermore, it has a much lower application rate than some alternative products. “It has a very low application rate – just 25-50 ml per tonne,” explains Tim. “One bottle will treat up to 100 tonnes of silage, whereas with other products you may have to keep stopping to refill the tank on the harvester.”

“If you aren’t careful when making your clamp, then all the additives in the world won’t make much difference,” acknowledges Nick. “However, when combined with a timely approach, a high standard of compaction and attention to detail, using Silasil Energy XD at the point of harvest means that wastage levels from the edges and top of the clamp are negligible. It’s quite incredible, but when I remove the sheets from a new piece of clamp, the feedstock looks like the day it was first put in.”