Development of an efficient anaerobic co-digestion process for garbage, excreta, and septic tank sludge to create a resource recycling-oriented society. (March 2017)

• Record Type: Journal Article
• Authors: Sun, Zhao-Yong; Liu, Kai; Tan, Li; Tang, Yue-Qin; Kida, Kenji
• Is Part Of: Waste management. Volume 61(2017)
• Page Start: 188
• Page End: 194
• Publication Date: 2017-03
• Subjects: Anaerobic co-digestion -- Garbage -- Excreta -- Septic tank sludge -- Biogas; Hazardous wastes -- Periodicals; Refuse and refuse disposal -- Periodicals; 363.728
• DOI: 10.1016/j.wasman.2016.11.021
• Languages: English
• ISSNs: 0956-053X

Abstract

Highlights: Regional bioenergy recovery was conducted by the anaerobic digestion of local wastes. A co-digestion process was developed based on the actual quantity of local wastes. The two-stage process consists of thermophilic liquefaction and mesophilic digestion. The developed process increased biogas evolution rate by up to approximately 22.9%. A sustainable resource recycling-oriented society was constructed in Ooki machi . 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 24 g/L/d was achieved. In the mesophilic digestion of mixed liquefied material and excreta (wet mass ratio of 1:1), biogas yield reached approximately 570 ml/g-VTS fed with a methane content of 55% at a VTS loading rate of 1.0 g/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.