Zero valent iron-assisted methane production from anaerobic digestion of microalgae Tetradesmus obliquus

Abstract Anaerobic digestion (AD) of microalgae presents a promising strategy for renewable methane production while contributing to atmospheric CO₂ reduction. Methane production potential from two strains of the microalga Tetradesmus obliquus (AG60 and AG10) was investigated. To enhance biomass hydrolysis, zero-valent iron (ZVI, Fe0) was added as an in-situ facilitator. Methane yields from microalgae treatments significantly exceeded those of the control (accumulative methane of 93.2 mL/g volatile solid (VS) from seed sludge only), with AG60 and AG10 producing 139.7 mL/g VS (algae only, p = 5.0 × 10 − 5 ) and 261.7 mL/g VS (algae only, p = 2.0 × 10 − 6 ), respectively. Quantitative PCR analyses done targeting 16 S rRNA and the methanogen-specific mcr A genes revealed an increased abundance of methanogens. Microbial community analysis supported the increase in hydrogenotrophic taxa such as Methanobacterium , suggesting a shift toward hydrogenotrophic methanogenesis in the AD. This analysis also showed an increase in the relative abundance of cellulolytic bacteria, supporting more efficient degradation of algal biomass. Despite complex microbial interactions, the addition of microalgae resulted in a stable and functionally enriched microbial community that facilitated efficient methane production. These results demonstrate the feasibility of using microalgal biomass as a viable substrate for AD without extensive pretreatment and highlight its potential role in the development of sustainable biogas systems and climate change mitigation strategies.