Long-term onsite monitoring of a sewage sludge drying pan finds methane emissions consistent with IPCC default emission factor

Mei Bai; Zhiyao Wang; James Lloyd; Dilini Seneviratne; Thomas Flesch; Zhiguo Yuan; Deli Chen

doi:10.1016/j.wroa.2023.100184

Long-term onsite monitoring of a sewage sludge drying pan finds methane emissions consistent with IPCC default emission factor

Water Res X. 2023 May 26:19:100184. doi: 10.1016/j.wroa.2023.100184. eCollection 2023 May 1.

Authors

Mei Bai¹, Zhiyao Wang², James Lloyd³, Dilini Seneviratne³, Thomas Flesch¹, Zhiguo Yuan², Deli Chen¹

Affiliations

¹ School of Agriculture and Food Science, Faculty of Science, The University of Melbourne, Parkville, Victoria 3010, Australia.
² Australian Centre for Water and Environmental Biotechnology (ACWEB, formerly AWMC), The University of Queensland, Brisbane, Queensland 4067, Australia.
³ Sewerage Planning - Service Futures, Melbourne Water, Dockland, Victoria 3008, Australia.

Abstract

As the wastewater sector moves towards achieving net zero greenhouse gas (GHG) emissions, quantifying and understanding fugitive emissions from various sewage treatment steps is crucial for developing effective GHG abatement strategies. Methane (CH₄) emissions from a sludge drying pan (SDP) were measured at a wastewater treatment plant in Australia for more than a year, using a micrometeorological technique paired with open-path lasers. The emission rate was tightly associated with sludge additions, climatology, and operational processes. The mean emission rate during the 90 weeks after initial sludge addition was 2.3 (± 0.8) g m^-2 d^-1, with cumulative emissions of approximately 32 t of CH₄. A dynamic temporal pattern of emissions was observed, highlighting the importance of continuous (or near-continuous) measurements for quantifying SDP emissions. A Methane Correction Factor (MCF) expressed as a fraction of the measured chemical oxygen demand of the sludge, was determined to be 0.17 after 63 weeks (the median operational cycle duration at the facility). This is broadly consistent with, albeit slightly less than, the IPCC default value of 0.2 for shallow anaerobic lagoons. These emission measurements will support wastewater utilities that employ open air sludge drying processes to develop effective GHG abatement strategies.

Keywords: fugitive methane emissions; inverse-dispersion model; long-term measurement; open-path Laser spectroscopic technique; sludge drying.