Temperature and organic loading dependency of methane and carbon dioxide emission rates of a full-scale anaerobic waste stabilization pond

CH4 and CO2 emission rates were measured in a full-scale anaerobic waste stabilization pond (AWSP) in Portugal and correlated with removed organic loading rate, and ambient air temperature. Strong correlation was found between biogas composition and removal efficiency. Correlation coefficients for CH4 and CO2 were 92.6% and 76.9%, respectively. The lowest liquid temperature at which the AWSP served as a primary sedimentation basin without any biological degradation, was found to be 11.7°C, with a total COD removal of 30%. First-order COD removal rate constant and temperature correction factor were 0.221 day−1 and 1.117, respectively. Biogas production rates varied between 28.68 and 83.17 l m−2 day−1. Average volumetric biogas production rate was 19.57 l m−3 day−1. Biogas volume changed during the day and 24 h-averaged value was 2.02 l m−2 h−1. Biogas conversion ratio was between 0.160 and 0.702 m3 kg COD−1removed. Percentages of CH4 and CO2 found in the biogas were between 52–80%, and 7–28%, respectively. CH4 production rates varied between 18.18 and 48.74 l m−2 day−1 depending on influent COD loading and liquid temperature. CO2 formation rates were between 3.08 and 9.79 l m−2 day−1. Mean CH4 and CO2 production were determined to be 82.34 and 14.40 m3 day−1, respectively. Volumetric production rates for CH4 and CO2 were obtained to be 13.54 and 2.37 l m−3 day−1, respectively.