Greenhouse Gas Emissions from an Anaerobic Pond Treating Domestic Wastewater under Tropical Climatic Conditions

56Greenhouse gas emissions from a full-scale anaerobic pond (AP) used for the treatment of domestic sewage were studied under tropical conditions. The GHG fluxes were measured using the static chamber technique. The results showed that the AP was a source of CH₄, CO₂ and N₂O emissions. CH₄ emissions ranged from 13.4 to 178.7 l.m^-2.d^-1, CO₂ from 9.3 to 130.5 l.m^-2.d^-1, while N₂O emissions ranged between 0.0016 and 0.013 l.m^-2.d^-1. According to the average fluxes, the emission rates into the atmosphere for CH₄ and CO₂ were 0.24 m³ CH₄.kg COD_rem ^-1 and 0.18 m³ CO₂.kg COD_rem ^-1, respectively. A COD mass balance calculation indicated that 37% of the influent COD was converted to CH₄ and 36% left the AP with the effluent. The rest of the COD was accounted for as volatile solids (3.5 %), CH₄ dissolved in the effluent (2.5%) and VSS in sludge settlement (21%). Finally, the GWP total for the AP studied was 37.8 kgCO_2eq.PE^-1.y^-1 or 2.18 kgCO_2eq.kgCOD_rem ^-1, which suggest that operating anaerobic ponds without considering the capture and reuse of biogas, may contribute to global warming.