The role of pH in the fermentative H2 production from an acidogenic granule-based reactor

The role of pH in the fermentative H2 production from an upflow acidogenic granule-based reactor was investigated in this study. Experimental results show that all H2 partial pressure, H2 production rate and H2 yield were pH-dependent, in the range of 2.8 × 104–5.2 × 104 Pa, 61–145 ml-H2 l−1 h−1 and 0.68–1.61 mol-H2 mol-glucose−1, respectively. The maximum H2 partial pressure was observed at pH 3.4, while both maximum H2 production rate and H2 yield were found at pH 4.2. Acetate, propionate, butyrate, i-butyrate, valerate, caporate and ethanol were present in the effluent of this UASB reactor, and their distribution was also pH-dependent. As pH was decreased from 4.2 to a lower level of 3.4 or increased to a higher level of 6.3, the fermentative type of this H2-producing reactor would shift from butyrate-type to caporate- or ethanol-type. Thermodynamic analysis was performed to explore the possible metabolic pathways of caproate and valerate formation. The metabolic pathway of caproate formation was pH-dependent, while that of valerate formation was pH-independent. A neural network model was designed, trained and validated. It was able to successfully describe the daily variations of H2 partial pressure and H2 yield of the reactor, and to predict its steady state performance at various pHs.