Document Type : ORIGINAL RESEARCH PAPER

Authors

1 Department of Environmental Science, Graduate school of Environmental and Life Science, Okayama University, Tsushima, Kita, Okayama, Japan

2 Department of Environmental Technology and Management, National University of Civil Engineering, Hai Ba Trung, Ha Noi, Vietnam

Abstract

Kinetic models which can express the behaviors of hydrolysis and biogas generation more precisely than the conventional models were developed. The developed models were evaluated based on the experimental data of six batch reactors. Anaerobic digestion test was co-digestion of food and vegetable waste with inoculating horse dung by 15% of the total wet weight, at the temperature of 37oC. For hydrolysis, the modified model was developed from an original first-order kinetic model. The modified first-order kinetic model was proved to be better than the original one with the hydrolysis rate constant in the range of 0.22-0.34/day and hydrolyzable rate of 0.80 to 0.84. Kinetics of carbon dioxide and methane were developed from a current potential model. The comparison between experimental data and modeling values had the high correlation of determination (0.9918-0.9998) and low root mean square errors (0.08-4.51) indicating the feasibility of the developed model. In which, the evolution of methane showed the rate constant in the range of 0.031-0.039/day. The carbon dioxide from fermentation accounted for 12-44% of the total observed carbon dioxide. Thus, separation of fermentation and methanogenesis by various reactors may reduce the price of methane enrichment significantly. There was a lag time between methanogenesis and fermentation in reactors (λ = 7-11 days). Also, the biogas yield was in the range of 431.6-596.9 Nml/g-VS with the CH4 concentration of 56.2-67.5%. The best methane yield (393.7 Nml/g-VS) was in a reactor with food waste to the vegetable waste ratio by 1.8:1 (wet basis) and C/N ratio by 25.4.

Graphical Abstract

Kinetics of carbon dioxide, methane and hydrolysis in co-digestion of food and vegetable wastes

Highlights

  • The kinetics of CO2 and CH4 were developed successfully, and their feasibility was proved by experimental data
  • Proposal of the modified first-order kinetic model was proved better than the conventional one
  • The ultimate biodegradable rate (49-69%) was much lower than the hydrolyzable rate (80-84%)
  • The methane yield was in the range of 260-394 Nml/g-VS with the best C/N ratio of 25.4.

Keywords

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