Application of a simple method to reduce the start-up period in a H2-producing UASB reactor using xylose

The major objective of dark fermentative H2 production (DFHP) is the significant enhancement of the H2 production performance from economic and engineering perspectives. An up-flow anaerobic sludge blanket (UASB) reactor based on H2-producing granules (HPGs) has been introduced, which results in the efficiency of the H2 production being improved significantly. However, the long start-up period remains a substantial obstacle in the stable operation of the UASB reactor. In the present study, a newly proposed operational strategy was employed to form the HPG using xylose as the feedstock, and this resulted in a successful reduction of the start-up period of the UASB reactor. After the mixed liquor in the continuously stirred tank reactor was transferred to the UASB reactor as a seeding source, the height of the HPG in the UASB reactor was progressively increased. In the UASB reactor, a maximum H2 yield of 2.98 mol H2/mol xylose and a stable H2 production rate of 9.98 L H2/L/h were observed at a hydraulic retention time of 6 h and a substrate concentration of 30 g COD/L. In this novel method, HPGs with an average particle size of 2.32 mm (0.1–4.7 mm) were successfully developed after 120 days and this is the first report documenting the successful formation of HPGs using xylose as feedstock in a UASB reactor.