A Guide to Making Compost from the Digested Fibre from Biogas PlantsFarms that make biogas using anaerobic digesters, can gain additional income from making and marketing their own compost products.
They can do this by using simple, but effective production methods based on their existing resources.
The simplest method is to use the windrow composting method.
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The Windrow Composting MethodTo do this the biogas plant operator simply heaps digested anaerobic digestion plant fibre in rows either out in the open, or under cover, for better water content control in hot countries.
It is turned over regularly with the shovel on a tractor, or with dedicated windrow turning machines.
This usually takes several months during which the water content and activity is measured for every batch, and until it becomes stable enough for bagging.
This process can be accelerated if the digested fibre for compost making is placed in a composting tunnel, and subjected to processing at a higher controlled temperature in a forced-air batch system.
Effectively, the digester output of fibre is loaded into large purpose-built bins, or compost tunnels, which have floors with perforated concrete slats inserted into them.
Biogas Digestate Maturation in a "Composting Tunnel"Pre-warmed air is blown by a compressor into a chamber below the slatted floor, and up through the compost.
The warm conditions, and abundant airflow speeds up the work of the bacteria and other organisms, which perform the composting process.
Later, once the compost is no longer active, it cools down cool from the high level of bacterial activity when earlier-on the aerobic bacteria create a considerable amount of heat.
In the compost tunnel, or bin method, the digestate fibre is ready to be taken out within a few weeks, and is again heaped up for a further few weeks, to mature.
The composted tilth, is then passed through a soil-shredder, to make it more friable, and for retail sales, it is usually bagged.
Worthwhile Additional Biogas Plant IncomeThis can often achieve a worthwhile added biogas plant income.
Sales are often made by selling this compost at the farm gate or through local garden centres.
However, experts have pointed out that a problem would occur if large numbers of individual farmers with digesters were to begin making and selling compost in the same area.
The Problem of Local Compost Market SaturationIn that area, local markets would soon become glutted.
There is no doubt that major retailers, or landscaping contractors, could become large buyers for this compost.
Unfortunately, the scale at which major retailers, or landscaping contractors wish to work, to do this at an economic price, is so large that few individual farmers are able to meet the quantity requirements.
Biogas expert Jonathan Letcher, in his Farm Digesters Book, and others have therefore proposed that to avoid this problem compost producers should work together to market their fibre compost.
That way they could produce enough composted fibre material, to meet the demands of major retailers, and landscaping contractors.
Unfortunately, many UK farmers who operate their own digesters reportedly feel they have neither the experience, the capital, nor time to set up their own compost-making business at all.
Digested fibre, could be a very useful resource, if fully used and composted.
Making Compost from the Digested Fibre from Biogas Plants Improves Anaerobic Digestion System SustainabilityBy processing and using it, the sustainability of the anaerobic digestion systems it would markedly raised.
Large-scale use of aerobic-composting, to finish converting the biogas digestate fibre, into a high quality product, would make it the great soil-enhancing material, it could be used throughout many countries.
Nevertheless, if digested fibre is to achieve its full potential, both in helping many more farms to afford a digester,
Local production by individual farms will never be big enough producers enough to break into this market.