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 (15N) has been used since the 1970s to track sewage pollution in 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 15N of wastewater particulate organic matter (POM) during the treatment process (Archana et al., 2016; Sebilo et al., 2006). We measured 15N in primary, secondary, and tertiary WWTP POM to assess the fractionation relationship between 15NDIN and 15NPOM in the processing of sewage wastes and further constrain 15NPOM values of WW particulates. The extent of treatment heavily influenced isotopic signatures, with 15NPOM 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 ‰) WWTPs. 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;15NAA), 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).