Ozonation By-products and Determination of Extracellular Release in Freshwater Algae and Cyanobacteria

Abstract

This work identifies the cyanobacterial and algal extracellular products (ECPs) and their derived byproducts during preozonation. Laboratory experiments were performed on two cyanobacterial species (Oscillatoria tenuisa and Microcystis aeruginosa) and one algal species (Chlorella sp.) dominating eutrophic reservoirs. Gas chromatography, coupled with high-resolution electron-impact mass spectrometry (GC/EI-MS), and high-performance anion-exchange chromatography (HPAEC) was adopted. Over 20 compounds were detected in the mass spectra analyses of the cyanobacterial and algal extracts (including cells and filtrates). The main identified ECPs were classified as monosaccharides, fatty acids, hydrocarbons, and aldehydes. Odor-causing substances were also present in the cyanobacteria, such as trans-1,10-dimethyl-trans-9-decalol (geosmin) and 2-methylisoborneol (2-MIB). The results from ozonated cyanobacteria and algae indicated that the dissolved organic carbon (DOC) content of culture suspensions increased during ozonation. Most of the additional DOC is produced by the increased liberation of ECPs to the bulk phase. Several byproducts were present in the ozonated cyanobacterial and algal cultures: a total of 22 different organic compounds were detected—mostly aldehydes and phthalates.