Orange County Water District (OCWD, CA) uses an advanced oxidation process (AOP) as the ultimate step for their wastewater treatment. Their overall purification process consists of standard initial, primary, and secondary treatments, performed at the nearby Sanitation District, followed by microfiltration (MF), reverse osmosis (RO), and ultimately an UV-H2O2 AOP. In this last step hydroxyl radicals (●OH) are generated through UV photolysis of the hydrogen peroxide. The high reactivity and non-selective reaction of this radical ensures degradation of any remaining chemical contaminants in the wastewater. However, within this train chloramines (NH2Cl, NHCl2, NCl3) are deliberately generated to prevent biofouling of the RO membranes through addition of a 12.5% basic hypochlorite solution. At the initial point of injection trichloramine (NCl3) is primarily formed through the reaction of the vast excess of hypochlorite at very basic pH with the wastewater ammonia. In addition to the problems these disinfectants cause in the AOP chloramines may also thermally react with organic constituents in the wastewater to produce harmful organochlorinated byproduct species. Speciation measurements on the RO permeate have shown that both mono- and dichloramine dominate, with only trace levels of trichloramine remaining. While considerable work has been reported for monochloramine reactions, very little is known about dichloramine. Therefore, in this study the thermal reactivity of dichloramine with a suite of amino acids, used as prototypical organic contaminants, was investigated using absorption spectroscopy and stopped-flow kinetics. Absolute second-order rate constants were measured, with the different amino-acid functionality providing insight as to how general organic matter in wastewater would react with dichloramine under wastewater treatment conditions.

Dichloramine reactivity with organic materials in wastewater

2019 Spring National Meeting

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