Methane Conference 2019

Industrial Methane Measurement Conference 2019 - Abstract

Abstract Title: Methane emissions from wastewater treatment facilities: measurements and carbon footprint evaluation
Presenter Name: Dr Antonio Delre
Co-authors:Prof Charlotte Scheutz
Company/Organisation: Technical University of Denmark
Country: Denmark

Abstract Information :

The main aim of a wastewater treatment plant (WWTP) is to remove pollution from the wastewater. However, the treatment produces diffusive and fugitive methane (CH4) emissions, which are challenging to measure, because they are emitted from a large area consisting of several smaller sources with different emission heights and physical shapes. CH4 emissions from WWTPs are diffusive, because they occur from sources scattered throughout the facility [1]. Additionally, they are fugitive, as they are unintended discharges escaping from process units [1]. Temporal emission variations, due to different operational conditions, pose an additional challenge in CH4 emission quantification from WWTPs. Quantification of plant-integrated CH4 emissions from WWTPs is possible using the Tracer gas Dispersion Method (TDM) [2]. The TDM is a ground-based remote sensing approach that combines the controlled release of a tracer gas from the WWTP with downwind atmospheric concentration measurements [2]. Seven Scandinavian WWTPs were investigated using the TDM. These facilities were different in terms of location, treatment capacity and treatment technologies applied. Plant-integrated CH4 emission rates were between 1.1 and 39.5 kg CH4 h-1, and corresponding CH4 emission factors were between 1.1% and 21.3% as kg CH4 (kg CH4 production)-1 [2]. The Life Cycle Assessment approach was used to investigate the contribution of CH4 emissions to the total carbon footprint of the studied plants. None of the WWTPs could be considered carbon-neutral, due to their positive net carbon footprint. CH4 emissions contributed between 12 and 30% of the total environmental burdens produced by the facilities [3]. Sensitivity and scenario analyses highlighted the importance of accurate CH4 emission factors, which are sensitive parameters whose small changes led to large changes in carbon footprint [3]. Additionally, CH4 emission factors were also responsible for the uncertainty of the net carbon footprint evaluation [3]. The study suggested a careful monitoring strategy during the inventory year, because very different results were obtained when using CH4 emissions measured during normal operational conditions and CH4 emissions measured during digester malfunctioning. Carbon footprint was up to 320 times higher when problems at digesters occurred [3]. Finally, using CH4 emission default values, provided by the international guidelines [4], resulted in a net carbon footprint up to seven times larger compared to the carbon footprint evaluated using measured plant-integrated CH4 emission rates [3]. [1] Delre A., 2018. Greenhouse gas emissions from wastewater treatment plants: measurements and carbon footprint assessment. Ph.D. thesis – Department of Environmental Engineering, Technical University of Denmark (DTU) Kgs. Lyngby. [2] Delre A., Mønster J., Scheutz C., 2017. Greenhouse gas emission quantification from wastewater treatment plants, using a tracer gas dispersion method. Science of the Total Environment 605–606, 258–268. doi:10.1016/j.scitotenv.2017.06.177 [3] Delre A., ten Hoeve M., Scheutz C., 2019. Site-specific carbon footprints of Scandinavian wastewater treatment plants, using the life cycle assessment approach. Journal of Cleaner Production 211, 1001-1014. doi: 10.1016/j.jclepro.2018.11.200 [4] IPCC, 2006. IPCC Guidelines for National Greenhouse Gas Inventories prepared by the National Greenhouse Gas Inventories Programme - Volume 5. https://www.ipcc-nggip.iges.or.jp/public/2006gl/vol5.html