Quantification of greenhouse gas emissions from sludge treatment wetlands

Abstract

Constructed wetlands are nowadays successfully employed as an alternative technology for wastewater and sewage sludge treatment. In these systems organic matter and nutrients are transformed and removed by a variety of microbial reaction and gaseous compounds such as methane (CH4) and nitrous oxide (N2O) may be released to the atmosphere. The aim of this work is to introduce a method to determine greenhouse gas emissions from sludge treatment wetlands (STW) and use the method in a full-scale system. Sampling and analysing techniques used to determine greenhouse gas emissions from croplands and natural wetlands were successfully adapted to the quantification of CH4 and N2O emissions from an STW. Gas emissions were measured using the static chamber technique in 9 points of the STW during 13 days. The spatial variation in the emission along the wetland did not follow some specific pattern found for the temporal variation in the fluxes. Emissions ranged from 10 to 5400 mgCH4/m2d and from 20 to 950 mgN2O/m2d, depending on the feeding events. The comparison between the CH4 and N2O emissions of different sludge management options shows that STW have the lowest atmospheric impact in terms of CO2 equivalent emissions (Global warming potential with time horizon of 100 years): 17kgCO2eq/PEy for STW, 36kgCO2eq/PEy for centrifuge and 162kgCO2eq/PEy for untreated sludge transport, PE means Population Equivalent.