Chukwu Onu

Date of Graduation


Document Type



Gas recovery from sanitary landfills is increasingly being viewed as a valuable resource for its potential as a source of fuel gas. The operation and performance of a two-phase laboratory-scale anaerobic digestion system for improved gas production was studied for a period of two years. The system consisted of a simulated landfill loaded with representative municipal solid waste (MSW) and a separate upflow anaerobic methane reactor. The concept under investigation was the separation of the acidogenic and the methanogenic phases of anaerobic fermentation, converting the sanitary landfill into an acid reactor and using a separate upflow fixed-film anaerobic reactor for methanogenesis. Acidic leachate from the landfill simulator was used as the influent substrate to the anaerobic reactor. The goal of the study was to improve both methane yield and concentration through nutrient addition and two-phase digestion of MSW. Sewage sludge was utilized to provide moisture, buffering capacity, nutrients, and an adequate microbial population. Single-phase systems with other enhancement techniques were also compared to the two-phase with sludge addition. Data from this study indicated that gas produced in the anaerobic reactor had methane concentration as high as 80 Mole % at the fixed-bed reactor (FBR) hydraulic retention time (HRT) of 7 days. The system reached a cumulative methane production rate of 78.6 L( S.T.P.)/kg dry waste at an estimated cumulative production rate of approximately 270 L( S.T.P.)/kg/yr. This performance was better than that reported in the literature for a similar type of feed. This study has also indicated that sewage sludge addition appears to be a successful enhancement technique for methane gas production from municipal solid waste. The addition of mineral nutrients and buffer solutions appears to have influenced the development of a dominant population of methanogenic bacteria in the FBR as indicated by the COD removal efficiency of 90% and 100% conversion of all influent organic acids. In terms of the overall system performance (as shown by the methane concentration, methane generation rate and organic waste stabilization), the two-phase system was superior to the one-phase technique currently in use for methane generation.