Kelsey Shaw

Topic

Nonsewered Sanitation Systems: Characterizing Anaerobic Degradation Pathways in Containment

Department of Civil Engineering

Date & location

• Friday, October 2, 2026

• 7:00 A.M.

• Virtual Defence

Reviewers

Supervisory Committee

• Dr. Caetano Dorea, Department of Civil Engineering, University of Victoria (Co-Supervisor)

• Dr. Linda Strande, Department of Civil Engineering, UVic (Co-Supervisor)

• Dr. Caterina Valeo, Department of Mechanical Engineering, UVic (Outside Member) 

External Examiner

• Dr. Tania Gómez Borraz, School of Engineering, University of Glasgow 

Chair of Oral Examination

• Dr. Kathryn Moran, School of Earth and Ocean Sciences, UVic

   

Abstract

Anaerobic degradation of wastewater stored in containments that form a part of the nonsewered sanitation (NSS) service chain are an increasingly important source of greenhouse gas (GHG) emissions, especially as the global reliance on onsite sanitation (i.e., septic and holding tanks) continues to grow. Current GHG inventory methodologies rely on assumptions that are transferred from centralized sewer-based wastewater treatment processes. However, these have yet to be verified in NSS and therefore cannot be used to adequately represent the physicochemical and microbiological processes governing emissions from septic and holding tanks. This limits the accuracy of climate impact assessments and the identification of effective mitigation strategies along the sanitation service chain. This dissertation investigates the pathways of anaerobic degradation and methane (CH₄) production during storage of nonsewered wastewater to improve the understanding of emissions from containments and inform the development of more accurate GHG inventory methodologies and sustainable sanitation planning. 

A mixed-methods experimental and observational approach was used, combining field measurements from 41 septic and holding tanks across rural southern coastal British Columbia, Canada, and urban Kampala, Uganda, with point source flux chamber measurements, microbial community and genomic characterization, and controlled activity experiments. Together, these approaches quantified CH₄ emissions, characterized technical, demographic and physicochemical characteristics of stored wastewater, related microbiological community composition and functional potential to anaerobic degradation pathways, and examined the metabolic pathways driving methanogenesis during storage in containments. 

Measured CH₄ emissions were highly variable between containments and study sites, and estimates differed substantially depending on the scaling and normalization approach used, highlighting limitations of current emission measurement and inventory methods used in the Intergovernmental Panel for Climate Change (IPCC) Tier 1 approach. No single physicochemical, technical, or demographic parameter consistently explained point source emission variability. Similarly, although microbial communities differed in taxonomic composition among containment units, methanogenic functional potential remained conserved, and neither community composition nor predicted methanogenic gene presence adequately explained measured emission variability. Controlled activity experiments demonstrated that both acetoclastic and hydrogenotrophic methanogenesis were active across all stored wastewater samples, with CH₄ production governed by differences in pathway expression and wastewater physicochemical characteristics rather than microbial community composition and abundance alone. 

These results show that different community compositions can support similar capacities for anaerobic degradation and CH₄ production during storage in containments while also showing that overall CH₄ production is lower than expected under assumptions derived from centralized sewer-based engineered anaerobic digesters and is largely confined to the soluble organic fraction. This has important implications as current planning approaches that assume substantial organic removal within containments are not only underestimating the emission potential reaching downstream treatment and disposal stages but are also overestimating the mitigation potential of storage itself. These findings demonstrate that by improving characterisation of influent nonsewered wastewater characteristics, fractions of anaerobically degradable organic matter, and controls on microbial activity will lead to the improvement of city‑scale emission estimates and support more effective climate mitigation strategies across the entire sanitation service chain.