Co-utilization of bread waste and harmful algal bloom-derived cyanobacterial biomass for Euglena gracilis cultivation: Turning waste and pollution into resources

초록

Microcystis aeruginosa is a harmful algal bloom (HAB)-forming cyanobacterium that poses significant environmental risks. Additionally, a large amount of bread waste rich in valuable carbon is discarded worldwide, resulting in both environmental and economic challenges. In this study, we sought to utilise M. aeruginosa biomass and bread waste for the cultivation of the beneficial microalga Euglena gracilis, thereby converting both HAB biomass and food waste into valuable resources. To this end, algal hydrolysate (AH) derived from M. aeruginosa and bread waste hydrolysate (BWH) were incorporated as components of an algal culture medium. Various proportions of AH were mixed with BWH, and the productivity of E. gracilis was assessed. Among all tested conditions, the 20 % AH medium resulted in the highest dry cell weight (9.01 g) of E. gracilis. During the subsequent bioreactor scale-up, biomass accumulation further increased to 9.87 g. Metabolite production was then compared under aerobic and anaerobic conditions using both AH and BWH based media. When cultivation transitioned from aerobic to anaerobic conditions, the lipid content of E. gracilis biomass increased from 12.2 % to 26.6 %. Furthermore, the fatty acid profile shifted toward a composition more suitable for jet fuel applications. This study presents a novel strategy demonstrating that both environmental pollutants (e.g., AH derived from HABs) and food by-products or waste (e.g., BWH) can serve as effective nutrient sources for microalgal cultivation, offering a promising approach for more economical and environmentally sustainable microalgae-based biotechnologies.

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