Dr. Linda Y. Tseng will present research based on the 2006 Intergovernmental Panel on Climate Change (IPCC) Guidelines for National Greenhouse Gas Inventories, which assumed that all carbon dioxide (CO₂) emissions generated by water resource recovery facilities (WRRFs; commonly wastewater treatment plants) during treatment were modern. As a result, CO₂ emissions from WRRFs were not included in greenhouse gas calculations. Since 2006, however, several studies have shown that a fraction of wastewater’s carbon is fossil in origin.
This presentation will focus on how fossil carbon content in primary influent was verified and how varying levels of fossil carbon are distributed across different unit operations within municipal WRRFs. The fossil carbon in wastewater subsequently generates fossil CO₂, and the resulting greenhouse gas emissions were compared to those calculated using the 2006 IPCC Guidelines. The inclusion of fossil carbon increased estimated greenhouse gas emissions by 13% (or 23% without an on-site energy recovery system, i.e., a digester producing biogas and biosolids from sludge).
Although total greenhouse gas emissions are higher when fossil CO₂ is included—particularly in systems with on-site energy recovery—much of the post-digestion fossil carbon remains in biosolids rather than biogas, presenting an opportunity for carbon sequestration during biosolids handling. This study, along with a handful of others, contributed to the IPCC’s 2019 guideline updates. By combining engineering knowledge in wastewater treatment, greenhouse gas accounting, and radiocarbon analysis, this presentation highlights how multidisciplinary collaboration can help address current and emerging environmental engineering challenges.
Speaker
Linda Y. Tseng
Assistant Professor, Department of Civil Engineering, The City University of New York
