A simple method to reduce the start-up period in a H2-producing UASB reactor

Introduction of an up-flow anaerobic sludge blanket (UASB) reactor apparatus to fermentative hydrogen production (FHP) enormously improves H2 production performance. However, the long start-up period required to form H2-producing granules (HPG) remains as a major obstacle. In the present work, a completely-stirred tank reactor (CSTR) was operated for 7 days, and the mixed liquor in the CSTR was transferred to a UASB reactor (UASBr (I)) as a seeding source. Coffee drink manufacturing wastewater (CDMW) was used as a feedstock, constituting the first attempt to form HPG from actual industrial wastewater. The strategy employed here was found to be more effective in developing HPG than directly starting from the UASB reactor (UASBr (II)), which is attributed to substantially higher active mass transfer in the CSTR. The average size of particles in the UASBr (II) blanket zone after 50 days of operation corresponded with that in the CSTR after only 7 days of operation. The drastic decrease of extracellular polymeric substance (EPS) protein concentration in the CSTR operation also indicates efficient removal of non-active biomass, the presence of which could adversely affect HPG formation. UASBr (I) showed a stable H2 yield and H2 production rate of 1.78 mol H2/mol hexoseadded and 2.76 L H2/L/h, respectively, and HPG with an average size of 1.9 mm were developed after 45 days. It appears that the abundant presence of divalent ions, especially calcium ions, contained in the CDMW facilitated HPG formation.