Effects of landfill void fraction and moisture content on the formation of aerobic areas in a semi-aerobic bioreactor

Abstract

The main disposal method for municipal solid waste (MSW), including the growing worldwide volumes of kitchen waste, involves transport to landfills. Because kitchen waste is mainly composed of organic matter and has a high moisture content, large amounts of leachate and landfill gas are generated when it is sent to landfills. Therefore, rapid waste stabilization is essential. In this study, four semi-aerobic bioreactors (named NS, SS, MS, and LS) were established with void fractions of 33.76%, 39.84%, 44.62%, and 41.31%, respectively. The results showed that the void fractions of landfill directly affected the gas flow path. When the landfill void fraction was small (e.g., NS), most airflow traveled directly through the pipeline and minimal airflow entered the waste layer. When the landfill void fraction was large (e.g., MS), air easily entered the waste layer and some air flowed into the gas vent with the landfill gas. As the reaction proceeded, the void fraction gradually decreased due to gravity-induced sedimentation. During the water addition experiment, the voids were occupied by water, leading to formation of an anaerobic area. Among the four bioreactors, only MS had negligible formation of an anaerobic zone in the center. Methane (CH₄) generation was detected only at the connection between the gas vent and the leachate collection pipe. A larger void fraction led to formation of a smaller anaerobic zone. The ratio of air flowing in pipeline was lowest in MS. These results indicated that a large void fraction promotes the decomposition of organic matter.