By Isabel Schestak
Cattles in Scotland, photographed by Isabel Schestak
By-product use from malt distilleries has a long tradition in Scotland, where it has probably been fed to cattle and sheep for more than 500 years (Crawshaw, 2001). Recently though, a shift from feed to bioenergy use has been observed, as incentives by the UK and Scottish government for renewable energy technologies have been taken up by the distillery sector (Bell et al., 2019). Though energetic use of by-products brings benefits for a distillery’s carbon footprint, from a water use perspective, also feed use might deserve recognition as environmentally favourable, when the protein rich by-products replace imported feed such as soybean meal. This has been shown already for greenhouse gas emissions, but not been looked at from a water perspective yet.
To find out which by-product use option performs best in terms of water use and to which extend it can improve the water footprint of spirits, we applied a recently developed methodology to the operations of a Scottish distillery. The method called AWARE (Available water remaining) does not only take into account the volume of water consumed for a process or product, but also the water availability or scarcity in the geographical area where the consumption takes place (Boulay et al., 2018). Water consumed in an arid region therefore is weighted stronger than that in a fairly water abundant area such as the UK. It is therefore not just a water, but a water scarcity footprint.
We looked at different scenarios for using spent grains and pot ale: 1) direct use as cattle feed in its fresh form and replacing a mix of imported soybean meal and domestic barley, 2) processing them first to dried distillers grains, thus producing a better conserving and more flexible to use feed before also replacing soy and barley, 3) processing to dried distillers grains but only replacing pure soy protein as feed and 4) anaerobic digestion to biogas, with subsequent combustion of the biogas to electricity and heat, and using the leftover digestate as fertiliser i.e. in total replacing grid electricity, heating fuel and fertilisers.
In the feed scenarios, both soy and barley were replaced in order to substitute an equal amount of protein and metabolisable energy found in the by-products.
First results showed that the water scarcity footprint of whiskey can be reduced by about 20% by using the by-products as either direct cattle feed (scenario 1) or generating biogas (scenario 4). Thus, there is no clear benefit for the use of by-products for renewable energy purposes, in contrast to the suggested reduction of GHG emissions through the government incentivised bioenergy option. The water savings are partially “invisible”, indirect savings though, achieved outside the distillery or even abroad and therefore do not directly improve a distillery’s footprint.
Similar observations have been made by Leinonen et al. (2018), who conducted an assessment on greenhouse gas emissions from different by-product use scenarios from single malt whiskey: in terms of percentage reduction of burdens through by-product use, higher reductions were achieved when by-products were used as feed in form of dried distiller’s grains, replacing soybean and barley feed (40%) than through biogas production and digestate application (27%). Again, these were partially indirect savings connected to land use change for the cultivation of soy abroad.
The study will be expanded to include other water footprint methods and data from further distilleries to enhance the reliability of the results. But already now we may question the environmental benefit from incentivising biogas production from distillery by-products.
References:
Bell, J., Farquhar, J., Mcdowell, M., 2019. Distillery by-products , livestock feed and bio-energy use in Scotland, Sruc.
Boulay, A.M., Bare, J., Benini, L., Berger, M., Lathuillière, M.J., Manzardo, A., Margni, M., Motoshita, M., Núñez, M., Pastor, A.V., Ridoutt, B., Oki, T., Worbe, S., Pfister, S., 2018. The WULCA consensus characterization model for water scarcity footprints: assessing impacts of water consumption based on available water remaining (AWARE). Int. J. Life Cycle Assess. 23, 368–378. https://doi.org/10.1007/s11367-017-1333-8
Crawshaw, R., 2001. Co‐product feeds: animal feeds from the food and drinks industries, 1st ed. Nottingham University Press, Nottingham.
Leinonen, I., MacLeod, M., Bell, J., 2018. Effects of alternative uses of distillery by-products on the greenhouse gas emissions of Scottish malt whisky production: A system expansion approach. Sustain. 10. https://doi.org/10.3390/su10051473