Septic tank performance in cold climates: challenges, stakeholder perceptions, and microbial dynamics
File(s)
Author(s)
Uteyeva, Aiman
Type
Thesis or dissertation
Abstract
This research investigated how extreme seasonal temperature fluctuations, ranging from –27ºC in winter to 31ºC in summer, affect the performance and microbial functioning of septic tank systems in cold-climate settings. Focusing on Kazakhstan, the study presents an integrated assessment combining stakeholder surveys, year-round field monitoring, and shotgun metagenomic analysis to examine how decentralised sanitation systems respond to natural temperature cycles.
Three aims were pursued: (i) examining stakeholder perceptions of sanitation challenges; (ii) assessing year-round septic tank performance under in situ thermal conditions; and (iii) characterising microbial and viral communities across seasonal temperature gradients.
A structured survey of 30 stakeholders across Kazakhstan's two coldest cities identified recurring challenges: inappropriate installation depth relative to frost penetration, reduced winter accessibility, irregular desludging, and limited technical oversight, providing new empirical evidence for context-specific management and policy responses.
Field monitoring of ten septic tanks over a complete annual cycle was supported by laboratory-scale, temperature-controlled anaerobic reactor experiments. Metagenomic analysis showed that anaerobic digestion was sustained by complex microbial consortia, including fermentative bacteria, syntrophic acetate-oxidising bacteria, sulphate-reducing bacteria, and hydrogenotrophic methanogens, with acetoclastic methanogens identified in septic tanks for the first time. Seasonal temperature variation was associated with coordinated shifts in microbial community composition and functional gene abundance linked to acetate activation, methanogenesis, and sulphate reduction.
Pathogen-associated bacteria persisted across all seasons and temperature conditions, indicating continuous public health exposure risk. Low temperatures selected for psychrotolerant Moraxellaceae; elevated temperatures enriched Pseudomonadaceae and Arcobacteraceae, taxa with clinical relevance and biofilm-forming capacity. Viral communities dominated by Caudoviricetes closely tracked prokaryotic dynamics, with significant correlations to anaerobic digestion guilds.
These findings provide mechanistic insight into temperature-driven functional reorganisation in septic tanks, supporting the development of more resilient sanitation strategies with implications for public health, groundwater protection, and climate resilience.
Three aims were pursued: (i) examining stakeholder perceptions of sanitation challenges; (ii) assessing year-round septic tank performance under in situ thermal conditions; and (iii) characterising microbial and viral communities across seasonal temperature gradients.
A structured survey of 30 stakeholders across Kazakhstan's two coldest cities identified recurring challenges: inappropriate installation depth relative to frost penetration, reduced winter accessibility, irregular desludging, and limited technical oversight, providing new empirical evidence for context-specific management and policy responses.
Field monitoring of ten septic tanks over a complete annual cycle was supported by laboratory-scale, temperature-controlled anaerobic reactor experiments. Metagenomic analysis showed that anaerobic digestion was sustained by complex microbial consortia, including fermentative bacteria, syntrophic acetate-oxidising bacteria, sulphate-reducing bacteria, and hydrogenotrophic methanogens, with acetoclastic methanogens identified in septic tanks for the first time. Seasonal temperature variation was associated with coordinated shifts in microbial community composition and functional gene abundance linked to acetate activation, methanogenesis, and sulphate reduction.
Pathogen-associated bacteria persisted across all seasons and temperature conditions, indicating continuous public health exposure risk. Low temperatures selected for psychrotolerant Moraxellaceae; elevated temperatures enriched Pseudomonadaceae and Arcobacteraceae, taxa with clinical relevance and biofilm-forming capacity. Viral communities dominated by Caudoviricetes closely tracked prokaryotic dynamics, with significant correlations to anaerobic digestion guilds.
These findings provide mechanistic insight into temperature-driven functional reorganisation in septic tanks, supporting the development of more resilient sanitation strategies with implications for public health, groundwater protection, and climate resilience.
Version
Open Access
Date Issued
2026-01-16
Date Awarded
2026-07-01
Copyright Statement
Attribution-NonCommercial 4.0 International Licence (CC BY-NC)
License URL
Advisor
Templeton, Michael R.
Grimes, Susan M.
Sponsor
Kazakhstan. Bilim zhane ghylym ministrligi
Publisher Department
Department of Civil and Environmental Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)