Pretreating mixed anaerobic communities from different sources: Correlating the hydrogen yield with hydrogenase activity and microbial diversity

In this study, granular and flocculated anaerobic mixed cultures were pretreated using heat, shock loading, acid, alkali, linoleic acid (LA) and 2-bromoethane sulphonic acid (BESA). Under mesophilic conditions (37 °C) and an initial pH value of 6.0, higher H₂ yields were observed for the flocculated cultures when compared to the granular cultures. The maximum yield for granular cultures treated acid, BESA or LA were statistically the same. Butyric acid fermentation was dominant in a majority of the treated cultures. The maximum hydrogenase evolution specific activity (ESA) (124 ± 8 U_e mg VSS⁻¹) at 37 °C correlated with the maximum H₂ yield for the LA treated flocculated cultures (1.69 ± 0.18 mol mol⁻¹ glucose). The microbial diversity data clearly showed that the low H₂ yield in the granular cultures was due to the lower proportion of H₂ producers. A principle component analysis (PCA) revealed that the LA treated flocculated and granular cultures were grouped together and showed more diversity in comparison to other pretreatment methods.