A meta-analysis of research trends on hydrogen production via dark fermentation

Abstract

This work provides a meta-analysis of the state-of-the-art research on H2 and value-added products production from biomass, via Dark Fermentation (DF) between 2015 and 2019. The meta-analysis data clusters are created considering inputs (i.e., feedstocks, and microorganisms used in DF), process conditions (i.e., feedstock pretreatments, and temperature, pH, working volume, substrate concentration in DF), yield and productivity of H2 and the most common by-products (i.e., acetic, lactic, butyric, propionic acids and ethanol). Agricultural and green residues were the most common feedstock (36.5%), followed by Aquatic biomass (29.8%). Pretreated feedstocks and mixed cultures were employed in 72% and 79% of the studies, respectively. The meta-analysis relates H2 high productivity to 6 ≤ pH ≤ 6.8 and 35 °C ≤ T ≤ 37 °C and H2 high yield to 5.5 ≤ pH ≤ 7.5 under mesophilic conditions. The paper elaborates on the production strategies tested at the laboratory scale for each of the DF-products mentioned above, highlighting the pros and cons towards improving yield and productivity and discussing what are the challenges to integrating DF in large-scale biorefining schemes for industrial production of H2 and value-added products.