Iron limitation effect on H₂/CO₂ biomethanation: experimental and model analysis

Trace metals are indispensable for the metalloenzymes involved for efficient H₂/CO₂ biomethanation. In-depth understanding of trace metals requirements of methanogens cannot only lead to robust and stable operation, but also can enhance CH₄ productivity. In this study, the effect of Fe, Mn, Co, Ni, Cu, Zn, Se, Mo and W on the H₂/CO₂ biomethanation was examined. In a period of nutrient deprivation, suppression of hydrogenotrophic archaea was revealed at higher feed gas rates, leading to a significant drop in CH₄ content and a concomitant rise in acetic acid concentration. After nutrient supplementation, the increase in Co, Ni and Fe concentrations were pivotal factors for enhanced methanogenic activity, leading to a CH₄ content of more than 98% in the outlet biogas and a sharp drop in acetic acid concentration. Moreover, mathematical modeling was employed to simulate the influence of the most prominent element, iron, on the biomethanation process. The amended BioModel demonstrated that Fe limitation suppresses hydrogenotrophic archaea which consequently leads to H₂ accumulation and growth of homoacetogenic bacteria.