Greenhouse gas emissions from ecotechnologies for wastewater treatment

Abstract

Greenhouse 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 m 3 CH4.kg CODrem-1 and 0.18 m 3 CO2.kg CODrem-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 kgCO2eq.PE-1 .y-1 or 2.18 kgCO2eq.kgCODrem-1 , which suggest that operating anaerobic ponds without considering the capture and reuse of biogas, may contribute to global warming.