Determination of oxidation rate constant for nodularin-r, saxitoxin, dc-saxitoxin, and neo-saxitoxin with conventional water treatment plant oxidants and advanced oxidation processes

Abstract

The effectiveness of chemical oxidation depends on the type of cyanotoxins present in the water and varies with the water quality parameters. This study investigated four cyanotoxins to understand their reactions with conventional drinking water treatment plant oxidants and with advanced oxidation. Kinetic rate constants between saxitoxin, and two variants (dcSTX and neoSTX), and nodularin-R with chlorine, monochloramine, permanganate, ozone, and hydroxyl radicals (UV-H₂O₂) were developed under different pH and temperature conditions. Nodularin-R kinetic rate constants were comparable to peer-reviewed microcystin-LR rate constants with reaction rates in the order of OH radicals > ozone >> chlorine > permanganate >> monochloramine. The speciation of saxitoxins with pH had a dominant effect on their reaction rates with the listed oxidants. Chlorine was the only oxidant effective for saxitoxins removal. The reaction rates of saxitoxins with OH radicals varied slightly with pH but were around two orders of magnitude less than microcystin-LR's.