Continuous lactate-driven biohydrogen production from the organic fraction of municipal solid waste

Abstract

The organic fraction of municipal solid waste (OFMSW) is a promising feedstock for biohydrogen production via dark fermentation. Lactate-driven dark fermentation (LD-DF) mitigates the impact of lactic acid bacteria (LAB) overgrowth, yet its application under continuous operation with real OFMSW remains underexplored. This study assesses the performance, stability, and microbial community structure of a continuous LD-DF system treating OFMSW. A continuously stirred tank reactor was operated for 26 days using OFMSW and inoculated with a well-established mixed culture for LD-DF, maintaining pH 6.5 and progressively decreasing the hydraulic retention time (HRT) from 18 to 6 h. Hydrogen yields ranged from 36.7 to 62.4 NmL H 2 /g VS as HRT decreased, corresponding to energy recoveries of 0.47–0.80 kJ/g VS. Shorter HRTs led to enhanced hydrogen productivities, reaching 6.9 ± 0.1 NL H 2 /L-d at 6 h HRT, which is among the highest values reported for OFMSW to date. In the short term, hydrogen production remained stable, with limited fluctuations in hydrogen productivity (stability index of 0.98). 16S rRNA gene sequencing revealed Lactobacillus as the dominant LAB and Bacteroides as a major genus. However, hydrogen production was likely supported by both dominant taxa (e.g., Bacteroides ) and low-abundance functional taxa (e.g., Clostridium sensu stricto) within a syntrophic LD-DF consortium. Lactate remained below 1 g/L throughout the operation, despite LAB presence in both the substrate and reactor, suggesting rapid lactate turnover towards hydrogen production. Overall, the results demonstrate that a lactate-driven DF reactor can effectively manage the biological and physicochemical complexity of real OFMSW under continuous operation.