Pretreatment of the Inoculum with Trichloromethane to Enhance Biohydrogen Production Via Two-Stage Batch Fermentation

Trichloromethane is often used as a chemical inhibitor to pretreat the inoculum to improve hydrogen yield in dark fermentation. In this study, five different doses of trichloromethane were used for methanogenic inhibition of methanogenic microbial community operating in stable (inoculum A) and anaerobic microbial community in natural environment (lake bottom slit, inoculum B). High concentrations of trichloromethane inhibited the activity of microbial community in the reactors and hindered the production of hydrogen and methane. At the same time, it would greatly reduce the pH, causing it to fall below the threshold of suitable hydrogen yield. In turn, ethanol-type fermentation was triggered, and the ethanol content of the system increased with increasing concentration of trichloromethane addition. The comprehensive assessment concluded that a 0.10% (v/v) trichloromethane concentration gave the best hydrogen yield performance in both inoculums. However, anaerobic microbial community in natural environment was able to produce hydrogen more efficiently than the operationally stable methanogenic microbial community. The highest cumulative hydrogen yield was 111.16, 34.36, and 72.76 mL/g VS in phase I (day 1-10), phase II (day 11-20), and the whole stage, respectively. In addition, the butyrate production in the reactor at this concentration was considerable, with an average yield of 21.3 g/L. [GRAPHICS]