Abstract
The work is devoted to the study of inhibitory factors limiting the yield of biohydrogen during the processing of lignocellulosic biomass (LCB). In this context, dark fermentation is considered one of the most promising biological methods for producing hydrogen, since it does not require an external energy source, is compatible with modern reactor technologies and allows the use of a wide range of substrates. The main barrier to its industrial application remains the accumulation of toxic compounds formed during the pretreatment of LCB and during fermentation. The work summarizes information on the composition and action of the main inhibitors. The results of the analysis showed that the yield of H₂ during TF reaches 2-4 mol/mol sugar (maximum ~3.8 mol/mol hexose), but drops significantly in the presence of: (i) furans (furfural 0.03-8.23 g/l; 5-HMF 0.09-1.59 g/l), (ii) phenolic compounds of lignin (vanillin, syringaldehyde), (iii) organic acids (formic, acetic, levulinic), (iv) inorganic ions and heavy metals (Zn, Cu, Cr, Ni, etc.), (v) ammonia and sulfates. Dosedependent effects and changes in microbial community composition are also discussed, such as the effect of pH, the reduction in Clostridium abundance due to furfural, or the increase in Clostridium and Ruminococcaceae abundance with the addition of 5-HMP. Thus, understanding the mechanisms of action of inhibitors and finding ways to reduce their impact are key areas for improving the efficiency of dark fermentation and its implementation as a sustainable technology for converting lignocellulosic biomass into biohydrogen.