Distillery by-products, livestock feed and bio-energy use: report

4. Feedstock use in the Scottish AD and bio-energy sectors

37. AD plants in the agricultural and distilling sectors utilise a range of feedstocks which vary depending on technology, availability and pricing. The table below lists the most common feedstock types by sector. There are no official data sets detailing actual usage of different feed stocks in AD plants in Scotland. Therefore, it is not possible to categorically define the quantities of distillery by-products used by AD plants. The approach taken has instead been to estimate the quantity of feedstock needed to operate the plants by sector (agricultural, distillery) as a proxy for actual usage. An explanation of these calculations is given in Appendix 4.

Table 10. AD plant feedstock types

Source: SRUC, AD Portal

38. Based on estimated bio-energy plant capacity (AD and CHP combustion), SRUC has estimated their likely feedstock requirement (in tonnes of dry matter equivalent). Using this approach it is estimated that between them the agricultural and distillery bio-energy sectors utilise an estimated 533,000 t DM of feedstock in dry matter terms, of which 268,000t DM is used in the agricultural AD sector and 278,000t DM is used by AD and CHP plants in the distillery sector (Table 11).

Table 11. Feedstock requirement of Scottish agricultural and distillery
AD and bio-energy plants

Source: SRUC

Bio-energy feedstock use compared to cattle feed requirements

39. The 547,000t DM of feedstocks estimated to be used in AD and CHP plants in Scotland are equivalent to 8.9% of the 5.98 million t estimated feed requirement of the Scottish cattle sector. Broadly speaking both the agricultural and distilling sectors are estimated to contribute approximately half each to this feedstock demand.

40. It must be stressed that it is difficult to make direct comparisons between the feed requirements of such different processes. While the agricultural and distillery energy plants utilise feedstocks that are suitable for feeding cattle, they also utilise other products that are not suitable nor economically feasible to feed cattle. These include dilute distillery washings, livestock manures and slurries and other wastes. Therefore, it is likely that the 8.9% figure is a modest overestimate since a small proportion by energy value of the feedstock used by AD plants would not be utilisable as cattle feed (washings etc). It is beyond the scope of the study to fully quantify this or to make an estimate of the breakdown of feedstocks used for each AD sector.