title: Kinetic characterization of thermophilic and mesophilic anaerobic digestion for coffee grounds and waste activated sludge.
abstract: This study was conducted to characterize the kinetics of an anaerobic process (hydrolysis, acetogenesis, acidogenesis and methanogenesis) under thermophilic (55 °C) and mesophilic (35 °C) conditions with coffee grounds and waste activated sludge (WAS) as the substrates. Special focus was given to the kinetics of propionic acid degradation to elucidate the accumulation of VFAs. Under the thermophilic condition, the methane production rate of all substrates (WAS, ground coffee and raw coffee) was about 1.5 times higher than that under the mesophilic condition. However, the effects on methane production of each substrate under the thermophilic condition differed: WAS increased by 35.8-48.2%, raw coffee decreased by 76.3-64.5% and ground coffee decreased by 74.0-57.9%. Based on the maximum reaction rate (Rmax) of each anaerobic stage obtained from the modified Gompertz model, acetogenesis was found to be the rate-limiting step for coffee grounds and WAS. This can be explained by the kinetics of propionate degradation under thermophilic condition in which a long lag-phase (more than 18 days) was observed, although the propionate concentration was only 500 mg/L. Under the mesophilic condition, acidogenesis and hydrolysis were found to be the rate-limiting step for coffee grounds and WAS, respectively. Even though reducing the particle size accelerated the methane production rate of coffee grounds, but did not change the rate-limiting step: acetogenesis in thermophilic and acidogenesis in mesophilic.
authors.affiliation: Key Lab of Northwest Water Resource, Environment and Ecology, MOE, Xi'an University of Architecture and Technology, Xi'an 710055, China; Dept. of Civil and Environmental Engineering, Graduate School of Engineering, Tohoku University, Aoba-ku, Sendai 980-8579, Japan.
authors.forename: Qian
authors.initials: Q
authors.lastname: Li
authors.affiliation: College of Engineering, China Agriculture University, Beijing 10081, China; Key Laboratory for Solid Waste Management and Environment Safety, Ministry of Education of China, Tsinghua University, Beijing 100084, China.
authors.forename: Wei
authors.initials: W
authors.lastname: Qiao
authors.affiliation: Key Lab of Northwest Water Resource, Environment and Ecology, MOE, Xi'an University of Architecture and Technology, Xi'an 710055, China.
authors.forename: Xiaochang
authors.initials: X
authors.lastname: Wang
authors.affiliation: Dept. of Civil and Environmental Engineering, Graduate School of Engineering, Tohoku University, Aoba-ku, Sendai 980-8579, Japan.
authors.forename: Kazuyuki
authors.initials: K
authors.lastname: Takayanagi
authors.affiliation: Graduate School of Environmental Studies, Tohoku University, Sendai 980-8579, Japan.
authors.forename: Mohammad
authors.initials: M
authors.lastname: Shofie
authors.affiliation: Dept. of Civil and Environmental Engineering, Graduate School of Engineering, Tohoku University, Aoba-ku, Sendai 980-8579, Japan; Graduate School of Environmental Studies, Tohoku University, Sendai 980-8579, Japan. Electronic address: yyli@epl1.civil.tohoku.ac.jp.
authors.forename: Yu-You
authors.initials: YY
authors.lastname: Li
mesh_terms: D000693:Anaerobiosis; D019149:Bioreactors; D040503:Coffea; D006868:Hydrolysis; D007700:Kinetics; D008697:Methane / Q000378:metabolism*; D008962:Models, Theoretical; D012037:Refuse Disposal; D012722:Sewage / Q000032:analysis*; D062611:Solid Waste / Q000032:analysis*; D013696:Temperature; D014865:Waste Disposal, Fluid
chemical_list: D012722:Sewage; D062611:Solid Waste; D008697:Methane
keywords: Anaerobic digestion; Mesophilic; Propionic acid degradation; Rate-limiting step; Thermophilic