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.

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




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