Comparative analysis of vermicompost quality produced from brewers' spent grain and cow manure by the red earthworm Eisenia fetida

Brewers' spent grain (BSG) is a by-product of brewing that is usually used as low-value animal feed, although it can be better exploited in biotechnological processes, such as vermicomposting. Here, the chemical, biochemical and microbiological qualifies of vermicomposts produced by the earthworm Eisenia fetida were evaluated using three substrates: BSG; cow manure (CM); BSG plus cow manure (1:1; BSG/CM). Over after 5 months of bio-conversion by earthworms and microorganisms (thereafter vermicomposting), BSG and BSG/CM showed reduced total organic carbon, and increased total nitrogen and total humic substances like (HSI), suggesting enhanced mineralisation and stabilisation. Suitability of BSG as substrate for earthworms was confirmed by the earthworm fatty acid profile, characterised by prevalence of C:17, C18:1, C18:2 and C18:3 fatty acids. Higher fungi and yeast abundance in BSG vermicompost was accompanied by higher dehydrogenase activity. E. coli, Salmonella spp. and Ochratoxin A levels were below the legal limits.