Statistical optimization of H2, 1,3-propanediol and propionic acid production from crude glycerol using an anaerobic fluidized bed reactor: Interaction effects of substrate concentration and hydraulic retention time

Abstract

The individual and interactive effects of the influent glycerol, Gin (2.9–17.1 g. L−1), and hydraulic retention time, HRT (0.76–9.24 h), were evaluated to optimize the production of hydrogen (H2 content and yield), 1,3-propanediol (1,3-PD) and propionic acid (HPr) in a mesophilic (30 °C) anaerobic fluidized bed reactor (AFBR). The maximum H2 content of 89.6% was obtained under the optimum conditions of 12.6 g. L−1 and 4.58 h, while the maximum H2 yield of 0.31 mol H2.kg COD applied−1 was obtained under the conditions of 18.0 g. L−1 and 7.72 h. For both responses, Gin was the more significant individual variable; however, the interactive effects between the Gin and HRT variables also suggest their significance in the process. The influence of the organic loading rate (OLR) on the production of 1,3-PD and HPr was also investigated in the reactor. The maximum yield of 1,3-PD was 0.87 g g glycerolconsumed−1 and was obtained under the conditions of 10 g. L−1 and 9.24 h, which is equivalent to an OLR of 23.62 kg m.−3.day−1. In contrast, HPr was produced in the highest yield of 0.57 g g glycerolconsumed−1 under the conditions of 15 g. L−1 and 2 h, which is equivalent to an OLR of 160.60 kg m.−3.day−1. The different specific conditions determined to favor each product enhance the mixed fermentation and the existence of competing metabolic pathways in the AFBR.