Zhu Jun
Department of Biological and Agricultural Engineering, University of Arkansas
In this project, the feasibility of biohydrogen production from liquid swine manure was investigated under different pH, hydrogen retention times (HRT), and glucose levels (Cg), using an anaerobic sequencing batch reactor system (ASBR). The results showed that the H2 content in biogas, H2 production rate, and H2 yield were all pH dependent and peaked at pH 5.0. For pH 4.4-5.0, the system could produce H2 with little methane, whereas for pH 5.3 or higher, methane was produced at a significant amount. The kinetic models from Gompertz equation were suitable for describing H2 production and substrate consumption, and pH had a profound effect on the kinetic parameters as well as on the substrate utilization. Uncontrolled pH could easily lead to system upset. Optimization of the ASBR system based on three variables, i.e., pH, HRT, and Cg was successfully achieved using response surface methodology with a central composite experimental design. The maximum values of H2 content, hydrogen production rate (HPR), and hydrogen yield (HY) were obtained under respective optimal conditions based on pH, HRT and Cg (H2 content = 42.7% and HPR = 26.1 L/d for pH 4.8, HRT 8h, and Cg of 18.7 g/L; and HY = 1.53 mol H2/mol hexose for pH 4.6, HRT 8h, and Cg of 20 g/L). A reconciled optimal condition at pH 4.8, HRT 11h, and Cg of 20 g/L was determined for the ASBR system to achieve 85% of the maximum values for all three hydrogen production performance parameters, with the observed results close to the predicted values.
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