title: Development of an efficient anaerobic co-digestion process for garbage, excreta, and septic tank sludge to create a resource recycling-oriented society.
abstract: In order to develop a resource recycling-oriented society, an efficient anaerobic co-digestion process for garbage, excreta and septic tank sludge was studied based on the quantity of each biomass waste type discharged in Ooki machi, Japan. The anaerobic digestion characteristics of garbage, excreta and 5-fold condensed septic tank sludge (hereafter called condensed sludge) were determined separately. In single-stage mesophilic digestion, the excreta with lower C/N ratios yielded lower biogas volumes and accumulated higher volumes of volatile fatty acid (VFA). On the other hand, garbage allowed for a significantly larger volatile total solid (VTS) digestion efficiency as well as biogas yield by thermophilic digestion. Thus, a two-stage anaerobic co-digestion process consisting of thermophilic liquefaction and mesophilic digestion phases was proposed. In the thermophilic liquefaction of mixed condensed sludge and household garbage (wet mass ratio of 2.2:1), a maximum VTS loading rate of 24g/L/d was achieved. In the mesophilic digestion of mixed liquefied material and excreta (wet mass ratio of 1:1), biogas yield reached approximately 570ml/g-VTS fed with a methane content of 55% at a VTS loading rate of 1.0g/L/d. The performance of the two-stage process was evaluated by comparing it with a single-stage process in which biomass wastes were treated separately. Biogas production by the two-stage process was found to increase by approximately 22.9%. These results demonstrate the effectiveness of a two-stage anaerobic co-digestion process in enhancement of biogas production.
authors.affiliation: College of Architecture and Environment, Sichuan University, No. 24 South Section 1, First Ring Road, Chengdu 610065, Sichuan, China.
authors.forename: Zhao-Yong
authors.initials: ZY
authors.lastname: Sun
authors.affiliation: Graduate School of Science and Technology, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555, Japan.
authors.forename: Kai
authors.initials: K
authors.lastname: Liu
authors.affiliation: College of Architecture and Environment, Sichuan University, No. 24 South Section 1, First Ring Road, Chengdu 610065, Sichuan, China.
authors.forename: Li
authors.initials: L
authors.lastname: Tan
authors.affiliation: College of Architecture and Environment, Sichuan University, No. 24 South Section 1, First Ring Road, Chengdu 610065, Sichuan, China.
authors.forename: Yue-Qin
authors.initials: YQ
authors.lastname: Tang
authors.affiliation: College of Architecture and Environment, Sichuan University, No. 24 South Section 1, First Ring Road, Chengdu 610065, Sichuan, China; Graduate School of Science and Technology, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555, Japan. Electronic address: kida@gpo.kumamoto-u.ac.jp.
authors.forename: Kenji
authors.initials: K
authors.lastname: Kida
mesh_terms: D000641:Ammonia / Q000378:metabolism; D000693:Anaerobiosis; D056804:Biofuels; D005191:Family Characteristics; D005735:Garbage; D007564:Japan; D059027:Recycling; D012722:Sewage; D014865:Waste Disposal, Fluid / Q000379:methods*
chemical_list: D056804:Biofuels; D012722:Sewage; D000641:Ammonia
keywords: Anaerobic co-digestion; Biogas; Excreta; Garbage; Septic tank sludge