Mechanistic insights into lignosulfonate-enhanced hydrogen production from waste-activated sludge via dark fermentation

Lignosulfonate, a byproduct of the paper manufacturing industry, has recently garnered research interest for its dual role in enhancing sludge management and facilitating resource recovery. However, its impact on hydrogen generation during dark fermentation remains poorly understood. This study investigates the underlying mechanisms driving lignosulfonate-enhanced hydrogen production. Batch experiments revealed that lignosulfonate-treated sludge exhibited enhanced hydrogen production during dark fermentation. Cumulative hydrogen production increased from 12.64 mL/g VS (volatile solids) to 26.10 mL/g VS within 10 d of fermentation as lignosulfonate dosage was raised from 0 to 80 mg/g VS. Further research found that lignosulfonate treatment altered sludge characteristics by modifying the concentrations and distributions of major metals, primarily Ca and Mg (up to 15 % removal), promoting organic matter solubilization and reducing sludge's surface charge (from −21.83 mV to −26.87 mV). Mechanism studies revealed that lignosulfonate treatment facilitated the transfer of organic matter from the solid to the liquid phase, offering more substrates for fermentation and promoting acidogenesis, a stage typically associated with hydrogen generation. Microbial communities structure analysis indicated that lignosulfonate treatment facilitated the enrichment of bacteria associated with hydrogen-producing (i.e., norank_f_JG30-KF-CM45, Tissierella, norank_o_MBA03). Additionally, lignosulfonate influenced the metabolic pathways governing both hydrogen production and consumption. These findings provide novel insights into lignosulfonate-assisted sludge treatment and offer practical implications for advancing sustainable sludge-to-energy technologies.