Abstract/Summary

1. Motivation, problem statement and aim Vast quantities of brewers’ grains are generated in the UK every year from the brewery industry. A large proportion of brewers’ grains are sold as a cheap, sustainable source of animal feed for cattle and other animals. This has substantial greenhouse gas mitigation benefits through substituting high carbon feeds such as those derived from soya. Furthermore, brewers’ grains reduce methane emissions from enteric fermentation further mitigating greenhouse gases. The conflict in Ukraine has contributed to rising energy, heating and fertiliser costs and increased pressure on breweries to utilise brewers’ grains as an anaerobic digestion feedstock to generate low cost heat, energy and biofertilizer onsite. This paper assesses the implications that switching brewers’ grains from an animal feed to anaerobic digestion feedstock would have on greenhouse gases and economics in the UK. 2. Methodology Greenhouse gas and economic implications were determined through conducting a Life Cycle Assessment and Life Cycle Costing respectively over a 20-year lifecycle for the following scenarios: Brewers’ grains to replace soy bean feeds in beef feed mix Brewers’ grains to replace beans (domestic, non-soy) in beef feed mix Brewers’ grains to generate combined heat and energy, and biofertilizer through anaerobic digestion Total quantities of brewers’ grains were determined for the UK. Net greenhouse gas mitigation (tCO2eq/tonne brewers’ grains) and cost savings (£/tonne brewers’ grain) were quantified per tonne of dried brewers’ grains for each scenario. The greenhouse gas and cost impacts were then scaled up to the UK-wide level. 3. Results Utilising brewers’ grains as an animal feed led to substantially greater greenhouse gas mitigation than anaerobic digestion, due to high mitigation potential from reduced enteric fermentation and substituting high carbon animal feeds. Conversely, anaerobic digestion of brewers’ grains was substantially more profitable than for animal feed, primarily due to the high cost of natural gas. 4. Conclusion Overall, the utilisation of brewers’ grains as an animal feed leads to substantial greenhouse gas mitigation which tends to be underestimated due to a lack of accounting for reduced methane from enteric fermentation in current IPCC methodologies. If economic pressures led to a transition from utilising brewers’ grains as an animal feed to an anaerobic digestion feedstock, then greenhouse gas mitigation from brewers’ grains would substantially decrease.