Optimization of Cattle Manure and Food Waste Co-Digestion for Biohydrogen Production in a Mesophilic Semi-Continuous Process

Shuang Liu,Haiyan Yang,Guoxiang Zheng,Longhai Li,Wenzhe Li

doi:10.3390/en13153848

Abstract

Biohydrogen production from organic solid waste has shown particular advantages over other methods owing to the combination of waste reduction and bioenergy production. In this study, biohydrogen production from the co-digestion of cattle manure and food waste was optimized in a mesophilic semi-continuous process. To maximize hydrogen production, the effects of the mixing ratio (the proportion of food waste in the substrate), substrate concentration, and hydraulic retention time (HRT) on the co-digestion were systematically analyzed using a Box–Behnken design. The results showed that strong interactive effects existed between the three factors, and they had a direct effect on the responses. Hydrogen was primarily produced via the butyrate pathway, which was accompanied by the competing heterolactic fermentation pathway. Propionate and valerate produced from lipids and proteins, respectively, were obtained along with butyrate. The optimal process parameters included a mixing ratio of 47% to 51%, a substrate concentration of 76 to 86 g L−1, and an HRT of 2 d. Under these optimal conditions, the hydrogen production rate and hydrogen yield were higher than 1.00 L L−1 d−1 and 30.00 mL g−1 VS, respectively, and the predicted results were consistent with the experimental data. The results indicate that the co-digestion of cattle manure and food waste is a practical and economically promising approach for biohydrogen production.

Highlights

In the past decade, owing to the limited sources of fossil fuels and their related environmental problems, renewable energy production has been a research focus [1,2,3]
The considerable variations in hydrogen production rate (HPR) and hydrogen yield (HY) indicate that the metabolic pathways in the co-digestion of cattle manure and food waste were complex
Significant deviations in HPR and HY were observed within a pH range of 5.06–5.20. These results indicate that even within the optimal pH range, HPR and HY are sensitive to hydraulic retention time (HRT) and substrate concentration

Summary

Introduction

In the past decade, owing to the limited sources of fossil fuels and their related environmental problems, renewable energy production has been a research focus [1,2,3]. The global production of organic solid waste (OSW), such as crop residue, food waste, and livestock waste, has continued to increase, owing to a rapidly growing population and improvements in economic status [4,5]. Dark fermentation, which is a process by which microbes produce hydrogen based on the biological conversion of organic matter, is a promising alternative method to manage OSW because biohydrogen has the highest energy content per unit weight, and it does not emit any harmful substances [7,8,9,10]. Dark fermentation with a single substrate, such as crop residue, food waste, or livestock waste, has attracted considerable attention [11,12,13,14].

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Results

Conclusion