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

The role of pH in the fermentative H(2) production from an upflow acidogenic granule-based reactor was investigated in this study. Experimental results show that all H(2) partial pressure, H(2) production rate and H(2) yield were pH-dependent, in the range of 2.8 x 10(4)-5.2 x 10(4)Pa, 61-145 ml-H(2)l(-1)h(-1) and 0.68-1.61 mol-H(2)mol-glucose(-1), respectively. The maximum H(2) partial pressure was observed at pH 3.4, while both maximum H(2) production rate and H(2) 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 H(2)-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 H(2) partial pressure and H(2) yield of the reactor, and to predict its steady state performance at various pHs.