In-depth observations of fermentative hydrogen production from liquid swine manure using an anaerobic sequencing batch reactor

In this study, experiments were designed to reveal in-depth information of the effect of pH and hydraulic retention time (HRT) on biohydrogen fermentation from liquid swine manure supplemented with glucose using an Anaerobic Sequencing Batch Reactor (ASBR) System. Five values of HRT (8, 12, 16, 20, and 24 h) were first tested and the best HRT determined was further studied at five pH levels (4.4, 4.7, 5.0, 5.3, and 5.6). The results showed that for HRT 24 h, there was a dividing H₂ content (around 37%) related to the total biogas production rate for the ASBR System running at pH 5.0. When the H₂ content went beyond 37%, an appreciable decline in biogas production rate was observed, implying that there might exist an H₂ content limit in the biogas. For other HRTs (8 through 20 h), an average H₂ content of 42% could be achieved. In the second experiment (HRT 12 h), the highest H₂ content (35%) in the biogas was found to be associated with pH 5.0. The upswing of pH from 5.0 to 5.6 had a significantly more impact on biogas H₂ content than the downswing of pH from 5.0 to 4.3. The results also indicated good linear relationships of biogas and H₂ production rates with HRT (r=0.9971 and 0.9967, respectively). Since the optimal ASBR operating conditions were different for the biogas/H₂ production rates and the H₂ yield, a compromised combination of the running parameters was determined to be HRT 12 h and pH 5.0 in order to achieve good biogas/H₂ productions.