Gas production during refuse decomposition

Gas production in sanitary landfills is a subject of much concern because of the potential hazards of CH₄ combustion and of groundwater contamination by CO₂. This study investigated the pattern of sanitary landfill gas production and the factors which affect it. A basis for study was prepared by examining factors which influence gas production in soil and sewage sludge digesters. The factors studied included moisture content, temperature, pH, alkalinity, Eh, and nutrition. It was then undertaken to determine whether or not this information was applicable to the landfill. A pattern for landfill gas production was proposed based on the assumption that an anaerobic environment would be achieved and maintained after refuse placement. Four phases were identified: I. Aerobic; II. Anaerobic Non-Methanogenic; III. Anaerobic Methanogenic Unsteady; and IV. Anaerobic Methanogenic Steady. The duration of these phase and the relative amounts of gases produced within each phase were studied. An investigation of information available on factors affecting gas production in sanitary landfills also was made. It was found that, in general, the principles developed from the study of gas production in other media were applicable to the landfill environment. It was found that gas production increases with increased moisture content but that conditions of high infiltration are often conducive to reduction in gas production apparently caused by modifications to the microbial environment. There appears to exist a typical pattern of temperature variation within the landfill with a peak temperature being reached during the initial phase of aerobic decomposition. The magnitude of this peak is related to the refuse temperature at placement. Subsequent temperatures are lower and tend to fluctuate with season. Optimum temperatures for gas production are in the range of from 30°C to 35°C, however, landfill temperatures are often lower than this. Optimum levels of pH and alkalinity exist which maximize gas production rates. The types and amounts of gas produced are influenced by refuse composition. A scheme was proposed to illustrate how the various factors influence landfill gas production and how these may interact. Those factors over which some control may be exerted during landfill design and operation were identified.