Characterization of Microbial Communities, Disinfection and Removal of Human Pathogenic Bacteria in Arctic Wastewater Stabilization Ponds

Abstract

Municipal wastewater management in Arctic Canada is different than in Southern Canada, mostly due to climatic and infrastructural constraints. Most arctic communities use trucked sewage collection systems followed by treatment in passive systems including wastewater stabilization ponds (WSPs). The objectives of this thesis were to determine if treatment of municipal wastewater in arctic WSPs successfully removes fecal indicator bacteria (generic Escherichia coli) and selected human bacterial pathogens (pathogenic eae-positive E. coli including O157:H7, Salmonella spp., Campylobacter spp., and Helicobacter pylori, and the non-enteric Listeria monocytogenes) and investigate the size, composition, diversity and potential function of bacterial WSP communities in relation to the impact of the Arctic climate, especially low temperatures, and treatment processes. This 3-year study (2012-2014) was conducted in the Nunavut communities of Pond Inlet and Clyde River with one-cell and two-cell WSP systems, respectively. Anaerobic conditions with an absence of algal blooms and constant pH values of 7.5-7.8 prevailed throughout the study period in the WSPs of both communities. The WSPs provided a primary disinfection treatment of the wastewater with a 2-3 log removal of generic E. coli. The bacterial pathogens E. coli O157:H7, Salmonella spp., L. monocytogenes, but not Campylobacter spp. and H. pylori, were detected in the treated wastewater, indicating human pathogens were not reliably removed. The bacterial population size and diversity was highly dependent on the treatment train and different geographic locations. However, the bacterial diversities in raw wastewater were not different between the communities. Seasonal and annual variations in temperature significantly (p<0.05) affected the disinfection efficiency, WSP bacterial diversities and potential functionalities. The best treatment effect in terms of disinfection and the removal of pathogen and nutrients was observed in the secondary pond of the two-cell WSP and in the middle of the treatment season. Future research should involve a quantitative microbial risk assessment to determine if the release of low levels of human pathogens into the arctic environment poses a human health risk and a bench-scale study to clarify the effect and significance of each variable (e.g., temperature, DO, pH and nutrients) to optimise the microbial functionality and removal of fecal bacteria.