M.Sc. Thesis Defence - Rachel N. Noddle
M.Sc. Thesis Defence - Rachel N. Noddle
Department of Earth and Environmental Sciences
Dalhousie University
Title: Bulk and Compound-Specific Nitrogen Isotope Biogeochemistry of Particulate Organic Material in Wastewater Treatment Plants
Abstract: Sewage wastewater is a significant global contributor to the degradation of coastal ecosystems globally. While stable isotope analysis (δ¹⁵N) has been used since the 1970s to track sewage pollution within the marine environment, a critical research gap exists in our understanding of the fractionation processes within wastewater treatment plants (WWTPs). Few studies have directly measured δ¹⁵N of wastewater particulate organic matter (POM) during the treatment process (Archana et al., 2016; Sebilo et al., 2006). We measured δ¹⁵N in primary, secondary, and tertiary WWTP POM to assess the fractionation relationship between δ¹⁵NDIN and δ¹⁵NPOM in the processing of sewage wastes and further constrain δ¹⁵NPOM values of WW particulates. The extent of treatment heavily influenced isotopic signatures, with δ¹⁵NPOM values decreasing (-1.1 ‰) from influent to effluent in the primary WWTP, in comparison to the increasing trends at the secondary (+3.5 ‰) and tertiary (+7.7 ‰) treatment.
In addition, we leveraged the processing of wastewater particulates as experimental chemostats to explore the mechanistic pathways of microbial degradation in organic matter. By using compound-specific isotope analysis of amino acids (CSIA-AA; δ¹⁵NAA), we were able to assess four general microbial metabolic patterns within primary and secondary WWTPs: de novo synthesis, animal-like heterotrophy, selective microbial resynthesis, and extracellular hydrolysis (Ohkouchi et al., 2017). We also compared the δ¹⁵NAA patterns to traditional indices, such as D/L ratios, Degradation Index, and the ΣV parameter, of organic matter degradation to present the first representation of δ¹⁵NAA in sewage wastewater and add new empirical evidence for metabolically distinct δ¹⁵NAA fractionation patterns in detrital organic material.
EXAMINING COMMITTEE: |
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|---|---|---|
| Dr. Ramon Filgueira | Dalhousie University | External Examiner |
| Dr. Owen Sherwood | Dalhousie University | Supervisor |
| Dr. Carolyn Buchwald | Dalhousie University | Reader |
| Dr. Amina Stoddart | Dalhousie University | Reader |
| Dr. James Brenan | Dalhousie University | Departmental Chair |
Time
Location
Milligan Room, 8007 LSC, Dalhousie University