Promotion of full-scale constructed wetlands in the wine sector: comparison of greenhouse gas emissions with activated sludge systems

Abstract

The aim of this study was to quantify and compare greenhouse gas (GHG) (i.e. carbon dioxide (CO2), nitrousoxide (N2O) and methane (CH4)) emissions from two full-scale winery wastewater and sludge treatment sys-tems (i.e. constructed wetlands (CWs) and activated sludge system) located in Galicia (Spain). GHG fluxeswere measured using the static chamber method in combination with an on-site Fourier transform infrared spectroscopy (FTIR) gas analyser in the CWs system. These on-site innovative techniques proved to be very accurateand reliable. In the activated sludge treatment systems, thefloating chamber method in combination with the FTIR gas analyser was used. Measurements were carried out during the vintage season, when winery wastewaterhas the highestflow and loads, and the rest of the year. Emission rates of CO2, N2O and CH4 in the CWs units(i.e. vertical flow, horizontal subsurface flow and sludge treatment wetlands) ranged from 1.35E+02 to 7.54E+04, 1.70E-01 to 3.09E+01 and-3.05E+01 to 1.79E+03 mg m-2day-1, respectively. In the case ofthe activated sludge units (i.e. reactor, secondary settler and sludge storage tank) emission rates CO2, N2O and CH4 ranged from 1.56E+04 to 1.43E+05, 1.13E+01 to 4.75E+01 and 2.52E+01 to 1.01E+03 mg m-2 day-1, respectively. Seasonally, daily and instantaneous variability in emissions as well as spatial variability was found. Comparing CWs with the activated sludge system, surface emission rates were lower in the CWs system in both seasons considered. Results highlighted that CWs are suitable technologies that can help to reduce GHG emis-sions associated with winery wastewater treatment.