The treatment of wastewater ultimately intended for reuse begins with the standard primary and secondary treatments, and is usually followed by additional filtration steps, especially microfiltration (MF) and reverse osmosis (RO). At the Orange County Water District, CA, treatment plant, their last treatment step is a hydrogen peroxide/UV Advanced Oxidation Process (AOP) where hydroxyl radicals are generated that react with, and quantitatively remove, residual unwanted chemical contaminants. However, during the MF and RO phases, biofouling of the membranes often occurs. To minimize this, a 12.5% basic hypochlorite solution is added to the waste stream prior to the MF. The hypochlorite reacts with ammonia present in the wastewater to produce chloramines, particularly trichloramine, at the initial point of injection.<br/>The small size and neutral charge of all chloramines means that they will readily pass through the filtration membranes to enter the AOP. Within the AOP, chloramines scavenge produced hydroxyl radicals, lowering the overall system ability to degrade remaining chemical contaminants. They also absorb UV light, which again reduces the overall remediation efficiency. In addition, in this time they can also undergo thermal reactions with the organic matter present. However, little data regarding the rate of reaction or products is known for these thermal reactions. The purpose of this study was to gain insight into the rates of reaction of trichloramine with organic matter. Here, amino acids were chosen as prototypical organic contaminants. Stopped flow and absorption spectroscopy experiments were used to measure trichloramine decay rates under various conditions. These solutions were buffered at approximately pH 12 to isolate deprotonated amine reactions. Typical kinetic data obtained were as shown in Figure 1, demonstrating a wide range of reactivity for trichloramine under AOP process conditions

Reactivity of trichloramine with organic species under AOP conditions

255th National Meeting (2018)

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