Environmental and economic impacts of using brewers spent grains for animal feed and anaerobic digestion

Over 130,000 tonnes of brewer's spent grains are generated annually in the UK. Most brewer's spent grains are utilised as a low-carbon animal feed, although anaerobic digestion provides economic benefits, through generating heat, energy, and biofertilizer. This study addresses a research gap by comparing both the economic and environmental impacts of using brewer's spent grains for animal feed versus anaerobic digestion. Specifically, it explores replacing brewer's spent grains-derived cattle feed with either high-carbon soya or UK-grown field beans, including dietary implications on methane generation and indirect land use change. Life Cycle Assessment and Life Cycle Costing were used to evaluate the environmental and economic impacts of utilising all brewer's spent grains generated in the UK for anaerobic digestion, as opposed to feeding cattle. Anaerobically digesting brewer's spent grains and using soya feed to replace brewer's spent grains as a cattle feed increased greenhouse gases by 39 Kt of CO 2 eq, while a field bean diet reduced emissions by 27 Kt of CO 2 eq. Additionally, the brewer's spent grain cattle diet required 6 and 8 thousand hectares less land than the field beans and soya diets respectively. However, anaerobic digestion of brewer's spent grains proved more profitable, offering an annual net economic benefit of £16 million. Thus, policy mechanisms such as an eventual ban could be introduced in order to phase out use of imported soya as an animal feed in the UK. Moreover, additional consultancy support, or interest free loans could be provided to facilitate breweries incorporating onsite anaerobic digestion. • AD of UK BSG provided a net economic gain of 16 million GBP. • AD of BSG increased GHGs by 39 Kt of CO 2 eq if soya was used as a replacement feed. • AD of BSG decreased GHGs by 27 Kt of CO 2 eq if field beans were the replacement feed. • AD of BSG increased land requirements which could increase GHGs. • Cattle growth rates and enteric fermentation had substantial implications on GHGs.