Cyanobacteria blooms are an area of concern for watershed management and protecting drinking water source quality. Some cyanobacteria produce cyanotoxins (microcystin-LR) that present a human health risk, and others produce metabolites (geosmin and MIB) that lead to taste and odor episodes at utilities. Cyanobacteria intracellular organic matter (IOM) contains high concentrations of these metabolites along with disinfection byproduct precursors. Drinking water treatment plants that apply oxidants upstream of physical removal processes to meet various treatment objectives have the potential to damage cell integrity and release metabolite-containing IOM. The objective of this study was to evaluate the feasibility of using fluorescence spectroscopy as a surrogate for IOM detection in a heterogeneous dissolved organic matter (DOM) matrix. IOM was isolated from three cyanobacteria species and characterized using fluorescence. The IOM fluorescence signatures were compared to Colorado River Water (CRW) to identify unique IOM attributes that could be used to monitor IOM release. IOM has a distinct optical signature by having a high fluorescence index (FI) greater than 2 and phycobiliproteins that fluoresce in the visible wavelength range. Phycobiliprotein fluorescence was decomposed using parallel factor analysis (PARAFAC), and all components found in the isolated IOM agreed with proteins known to occur in cyanobacteria. Interaction effects between IOM and DOM were evaluated and found that the highly fluorescent phycobiliproteins are quenched by the presence of DOM. Phycobiliproteins were also readily oxidized decreasing their fluorescence intensity. Both the quenching interactions and rapid oxidation limit their utility as an optical surrogate.   FI proved to be the most successful surrogate for IOM release by monitoring compositional changes of the DOM. Bench-scale oxidation of cyanobacteria cells in CRW demonstrated the utility of FI for detecting IOM release.

Fluorescence spectroscopy as an indicator for cyanobacteria organic matter release by oxidation processes

248th National Meeting (2014)

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