Biohydrogen production through dark fermentation of organic waste: evaluation of pretreatment methods

Pretreatment of organic substrates is a critical step in enhancing the efficiency of biological hydrogen (bioH₂) production via dark fermentation. This research presents and discusses the effects of different pretreatment methods on a selected substrate, spent coffee grounds (SCGs), aiming to evaluate their influence on hydrogen yield and productivity. In addition to a control condition referred to as "non-pretreatment," all tested substrates underwent preliminary size reduction and dilution as standard treatments. The study investigates and compares the application of chemical agents (acid hydrolysis with H₂SO₄) and physical processes (ultrasound). The results show a significant influence of pretreatment on substrate biodegradability and hydrogen production. Surprisingly, the highest cumulative hydrogen volume (~280 mL H₂) was observed for the non-pretreated substrate, suggesting that the combination of size reduction and dilution alone was sufficient to enable efficient fermentation. The ultrasound-treated substrate demonstrated faster kinetics and an earlier peak in hydrogen production, though with a slightly lower total volume (~240 mL H₂). Conversely, acid hydrolysis resulted in poor hydrogen yields, likely due to the formation of inhibitory by-products or limited hydrolysis efficiency under the tested conditions. These findings highlight that not all pretreatments enhance biohydrogen production: in some cases, mild or no pretreatment may outperform more aggressive methods. The results underscore the importance of tailoring pretreatment strategies based on the specific substrate characteristics and process goals, providing valuable insights into sustainable hydrogen production from organic residues.