Microbial ecology of wastewater treatment and residuals

Abstract

Every day, municipal activities and industrial processes consume and contaminate a large volume of water, which must then be treated before being returned to aquatic ecosystems. Wastewater treatment plants (WWTPs) use physical, chemical, and microbiological processes to clean the water, which in turn produces sludge. Sludge, an organic waste product, historically has been landfilled, but can be diverted from landfills if it used as a resource for biogas methane production or as organic fertiliser on damaged ecosystems. Microbial communities are the ecosystem engineers driving changes in organic matter and chemistry throughout wastewater treatment, methane production, and soil development, and modern mass sequencing tools allow us to survey the microbial community composition associated with different environments and outcomes. In this thesis, I looked at the microbial communities and treatment endpoints of interest associated with anaerobic digestion, land application, and production of WWTP sludge.

In my first research project, I examined methane production from anaerobic digestion of 11 pulp and paper mill WWTP sludges. Mean methane potential varied between sludges, and kraft mill primary sludges produced more methane than biosludge, whereas other mills showed inhibition in primary sludge. Methane production only occurred in sludges with high diversity prior to anaerobic incubation. In my second project, 8 treatments of organic-derived industrial residuals, including WWTP sludges and controls, were applied to plots in semi-barren smelter- impacted land around Sudbury, and trees were planted to evaluate value in ecosystem restoration for the Sudbury Regreening Program. Treatment effect on soil chemistry and the microbial community was largely associated with pH changes, and soil metal concentrations did not increase beyond regulatory limits, so treatments with liming capacity are likely suitable for use in the Sudbury Regreening Program. In my third project, I surveyed the microbial communities of 4 WWTPs around Sudbury in summer and winter to compare seasonal differences. WWTPs had differences in bacterial, archaeal, and eukaryotic communities in summer and winter. Archaeal community changes showed similar patterns across WWTPs, but bacterial communities had different patterns for WWTPs that demonstrated nitrification, and eukaryotic communities had different patterns across all WWTPs. Overall, I demonstrated similarities and differences in microbial communities degrading organic matter across multiple treatments in association with WWTP sludge.