Effect Of Leachate Recirculation On Methane Generation Of A Bioreactor Landfill

Municipal solid waste (MSW) disposal is of current concern due to the green-house effect and rising temperature all around the globe. Landfill gas is generated from aerobic & anaerobic biodegradation of organic materials in municipal solid waste (MSW) landfill. Along with leachate, generation of Methane happens to be a by-product of the entire biodegradation process in MSW landfills. Conventional landfilling or dry cell concept minimizes the amount of moisture infiltration into the waste. In contrast, Enhanced Leachate Recirculation (ELR) or bioreactor operation facilitates leachate recirculation and distribution through the landfill that leads both reduction of time for waste stabilization and enhancement of gas generation. The influence of leachate recirculation was investigated from a US muni ipal solid waste landfill (City of Denton, TX) where landfill gas generation and gas composition data were monitored for ten (10) individual lateral pipes H1 to H10. Three (3) from those ten (10) pipes from current working area A were considered for this research to determine the influence of moisture injection for a period of 365 days. MSW landfill gas composition and landfill gas flow were measured from each individual pipe (H2, H7 and H6). The average flow rate from the bio-reaction beneath the recirculation pipes (H2 and H7) was close to 15 ft3/min whereas, for the non recirculating pipe (H6), the average flow rate was around 10 ft3/min. From the gas composition test results, the recirculated gas pipes H2 and H7 provided methane percentage (%CH4) close to 60% whereas the non-recirculating pipe provided around 45%. In addition, the distribution of methane concentration was fairly even for the recirculaing pipes compared to the non-recirculating pipes. Gas flow rate and composition were highly affected with additional moisture intrusion into refuse mass in the form of recirculated leachate. The field flow rate was compared with the predicted flow rate to evaluate the efficiency of the leachate recirculation system and gas collection system.