Homoacetogenesis outcompetes GHG emissions during microalgal dark fermentative hydrogen production

One of the best ways to produce clean and carbon-free energy is the H₂ production using microalgal biomass, which can improve the problems associated with renewable energy, climate change, and GHG emissions. Microalgal hydrogen (H₂) production through dark fermentation (DF) or photo fermentation (PF) is the most sustainable pathway. The use of microalgae alone and in co-culture with bacteria under DF conditions was tested experimentally for H₂ and CO₂ generation as a byproduct of anaerobic digestion. It was observed that microalgal control produced the highest volume of 4018 mL/L of total gas with the peak volume of 326 mL H₂/L and the least generation of 152 mL CO₂/L compared to the co-cultures in DF conditions. Also, the abundant generation of nitrogen (N₂) at 2478 mL/L and oxygen (O₂) at 606 mL/L was observed, one of which is an inert gas and the other is essential for living organisms. The study based on experimental data concluded that homoacetogenesis process during DF of microalgae prevails the methanogenic process and further converts the generated CO₂ into acetate by consuming H₂. The remaining H₂ and CO₂ are still 6.5% higher and 3.2% less than the H₂ and CO₂ generated by microalgae during PF.