Impact of brewer's spent grain on freshwater and marine harmful algal bloom species Harmful Algae

Barley straw bales are commonly used to control cyanobacterial growth in lakes, but the method is time-consuming, labor-intensive, and its effectiveness requires deployment of bales prior to bloom formation. This study investigates brewer's spent grain (BSG), a byproduct of the brewing process, as an alternative source of allelopathic chemicals shown to negatively impact toxic microalgae. Water extracts of BSG, barley straw, and Sargassum natans were tested for their ability to inhibit the growth of toxin-producing (Microcystis aeruginosa and Karenia brevis) as well as non-toxin-producing (Tetradesmus obliquus and Phaeodactylum tricornutum) algal species. BSG extracts at concentrations above 250 mg/L effectively inhibited the growth of both freshwater and marine toxin-producing species (M. aeruginosa and K. brevis), while exhibiting no significant effect on the diatom and chlorophyte species tested (T. obliquus and P. tricornutum). Additional experiments using antibiotics with K. brevis suggest that growth inhibition may be mediated by changes in the bacterial community, though the specific mechanism of M. aeruginosa death remains unresolved. A microcosm experiment further evaluated the impact of BSG extract on a natural bloom of cyanobacteria (Raphidiopsis raciborskii) in lake water. Application of 250 mg/L BSG extract to natural lake water shifted the community composition from cyanobacteria to chlorophyte dominance. These findings highlight the potential use for a brewery's waste product as a cost-effective tool for managing harmful algal blooms. However, the high concentrations required, excess nutrient content in BSG, and impact on bacterial communities indicate limitations for large-scale application. Grant no. NA18OAR4170070