Comparative environmental sustainability assessment of biohydrogen production methods

As energy crisis is recognized as an increasingly serious concern, the topic on biohydrogen (bioH₂) production, which is renewable and eco-friendly, appears to be a highly-demanding subject. Although bioH₂ production technologies are still at the developmental stage, there are many reported works available on lab- and pilot-scale systems with a promising future. This paper presents various potential methods of bioH₂ production using biomass resources and comparatively assesses them for environmental impacts with a special emphasis on the specific biological processes. The environmental impact factors are then normalized with the feature scaling and normalization methods to evaluate the environmental sustainability dimensions of each bioH₂ production method. The results reveals that the photofermentation (PF) process is more environmentally sustainable than the other investigated biological and thermochemical processes, in terms of emissions, water-fossil-mineral uses, and health issues. The global warming potential (GWP) and acidification potential (AP) for the PF process are then found to be 1.88 kg-CO₂ eq. and 3.61 g-SO₂ eq., which become the lowest among all processes, including renewable energy-based H₂ production processes. However, the dark fermentation-microbial electrolysis cell (DF-MEC) hybrid process is considered the most environmentally harmful technique, with the highest GWP value of 14.6 kg-CO₂ eq. due to their superior electricity and heat requirements. The water conception potential (WCP) of 84.5 m³ and water scarcity footprint (WSF) of 3632.9 m³ for the DF-MEC process is also the highest compared to all other processes due to the huge amount of wastewater formation potential of the system. Finally, the overall rankings confirm that biological processes are primarily promising candidates to produce bioH₂ from an environmentally friendly point of view.