Anaerobic digestion waste as a nutrient source for closed-loop alkaline cultivation of a cyanobacterial consortium

The use of anaerobic digestion (AD) wastes as nutrient sources for cyanobacterial cultivation offers a sustainable path to closed-loop bioproduction. This study investigated the potential of liquid and solid digestates from a Candidatus Sodalinema alkaliphilum consortium to support community growth under alkaline conditions. While the AD waste provided sufficient nutrients for growth, the culture crashed by the third cultivation cycle, even after dilution of the digestate to mitigate potential inhibitory factors. Microbial community and metabolite analyses suggested that toxic compounds, including 2,4-di-tert-butylphenol (DTBP), likely played a role in the culture crashes, while Roseinatronobacter and other bacteria or archaea from the digestate were unlikely to be direct causes. This study highlights the potential challenges of using AD waste for the cultivation of cyanobacteria in a closed-loop system and emphasizes the need for further investigation into the mechanisms driving culture crashes to enhance the sustainability of this biotechnological approach. • Anaerobic digestate contained sufficient nutrients, but the bioavailability of nutrients was lacking. • Cyanobacterial cultures crashed by the third growth cycle when digestate was used. • Crashes could not be explained by digestate turbidity and nutrient levels. • Roseinatronobacter and other bacteria or archaea from the digestate are unlikely to have caused culture crashes. • The microbially synthesized toxin 2,4-di-tert-butylphenol may have contributed to cyanobacterial population instability.