Enhancing the CH4 yield of anaerobic digestion via endogenous CO2 fixation by exogenous H2

• H2 can be generated from anaerobic iron corrosion in anaerobic digestion (AD).
• The generated H2 can be utilized for converting CO2 to CH4.
• With CO2 fixation, enhancement up to 61% in the CH4 yield is achieved.
• The added iron can also achieve phosphorus removal from the AD supernatant.

A large amount (25–60%) of degraded organics is converted directly to CO2 during anaerobic digestion (AD) process, which substantially lowers the energy (methane, CH4) yield. In this study, endogenous CO2 fixation by H2 from in-situ iron corrosion was explored to enhancing the CH4 yield. The results demonstrated that a substantial enhancement (up to 61%) in the CH4 yield could be achieved with both nano-scale zero-valent iron (NZVI) and waste iron scraps (WIS) being the added iron. Additionally, the added iron could also achieve effective phosphorus removal from the AD supernatant.