Effect of Inoculum Pretreatment and Operational Mode of Reactor on BioH 2 Production from Nixtamalization (Nejayote) and Abattoir Wastewater

Dark fermentation process appears to be one of the most promising techniques to obtain clean energy, however, there are some limitations to this process. In the present study, stirred tank reactors under different modes [batch (BR) and continuous (CR)] were used to determine the evolution of hydrogen-producing microbial communities when nixtamalization (nejayote) and abattoir wastewater were co-digested. The inoculum consisted of granular sludge subjected to (a) thermal treatment (TT); and (b) UV irradiation. When the inoculum underwent TT (15 min at 100 °C) in BR (40 RPM, 35 ± 1 °C, pH 5.50 ± 0.05), the highest cumulative biohydrogen (bioH 2 ) content was obtained (350 mL). In this case, the organic matter degradation reached 70%. In addition, the sequencing analysis showed Clostridium butyricum was the predominate strain (68–87%) between 48 and 72 h of the reaction. Conversely, when UV-pretreated inoculum was used, Clostridium butyricum only made up 1% after 60 h of reaction. The CR was operated for 20 cycles at a hydraulic retention time of 6 h. Volatile fatty acids confirmed butyrate acetate fermentation. Herein, the bioH 2 yield was generated at a fivefold rate compared to previous studies. Specifically, 223 mL H 2 g −1 total volatile solids and 8 mL H 2 L −1 h −1 were produced. Moreover, Clostridium was present at 59–62% after 14 cycles, confirming a better efficiency in bioH 2 production when the reactor works in continuous mode. Graphical Abstract