Disproportionate Changes in Composition and Molecular Size Spectra of Dissolved Organic Matter between Influent and Effluent from a Major Metropolitan Wastewater Treatment Plant
Hui Lin, Kazuaki Matsui, Ryan J. Newton, Laodong Guo
Abstract
Dynamic changes in the abundance, composition, and size spectra of dissolved organic matter (DOM) in different size-fractions between influent and effluent from Milwaukee metropolitan wastewater treatment plants (WWTPs) were evaluated using size-fractionation, excitation–emission matrix (EEM) coupled with parallel factor analysis (PARAFAC), and ΔEEM approaches. Up to 82.7% of DOC, 43.1% of total dissolved nitrogen (TDN), and 52.4% of chromophoric-DOM (CDOM) were removed from the influent, indicating different reactivity/degrability and disproportionate removal between DOM species. Within the CDOM pool, both the aromaticity and humification-index increased after treatments while the biological-index remained similar, showing a preferential removal of autochthonous DOM and the protein-like components, resulting in a higher abundance of humic-like components in the effluent but little change in the DOM size spectra. Up to 3%–5% differences were measured in the bulk DOM concentrations between the 0.22 and 0.7 μm filtrates. In addition, DOM in the 0.22–0.7 μm size-fraction contained almost only protein-like components, showing a high DOM heterogeneity. High levels of photochemically and biologically labile DOM in the effluent, with a higher molecular weight and lower DOC/TDN ratio, may alter the microbial community and biogeochemical processes in coastal Lake Michigan. Long-term and concurrent characterization of DOM in both effluent and receiving waters is needed to better understand the environmental/ecological roles of DOM as it moves through WWTPs and into the natural environment.