Effect of sodium dodecylbenzene sulfonate on hydrogen production from dark fermentation of waste activated sludge.

Sodium dodecylbenzene sulfonate (SDBS), a typical surfactant being widely used in various applications, was highly accumulated in waste activated sludge. To date, however, its effect on hydrogen production from dark fermentation of sludge has not been documented. The work therefore aimed to explore whether and how SDBS affects hydrogen production. Experimental results showed that with an increase of SDBS from 0 to 30 mg/g TSS, the maximal hydrogen yield increased from 2.47 to 10.73 mL/g VSS (without any treatment) and from 13.05 to 23.51 mL/g VSS (under free ammonia pretreatment). Mechanism exploration showed that SDBS lowered surface tension, facilitated organics transfer from solid to liquid. SDBS also destroyed hydrogen bonding networks of protein, promoted macromolecular organics degradation. Besides, SDBS improved the electric charge in organics, then weakened the mutual repulsion, improved adsorb, interact and promoted the availability of reaction sites between anaerobes and organic substances. Enzyme activity analysis showed that SDBS not only improved the activities of enzymes related to hydrolysis and acidification processes, but also inhibited the activities of homoacetogens and methanogens. SDBS presence lowered sludge ORP and created an environment which was helpful to the growth of butyric-type bacteria, thus enhanced butyric-type fermentation, which contributed hydrogen production largely. Microbial community analysis revealed that SDBS existence affected distributions of microbial populations, and increased the abundances of hydrogen producing microorganisms (e.g., unclassified_f_Synergistaceae). PICRUSt2 analysis showed that SDBS reduced hydrogenotrophic methanogens activity for its inhibitory effect on the biotransformation of 5,10-Methenyl-THMPT to 5-methyl-THMPT.