Chloramines applied to control membrane biofouling in potable reuse trains pass through reverse osmosis membranes, such that downstream UV/H2O2 advanced oxidation processes (AOPs) are de facto UV/H2O2-chloramines AOPs. Current models for UV/chloramine AOPs are unable to simultaneously predict the loss of chloramines and contaminants, such as 1,4-dioxane, due to the inaccurate chloramine quantum yields and ignorance of the fate of *NH2. This study determined quantum yields for NH2Cl (0.35) and NHCl2 (0.75). Incorporating these quantum yields and the radical scavengers formed from *NH2 (i.e., NO and NO2-) was important for simultaneously modeling the loss of chloramines, H2O2 and 1,4-dioxane in the UV/H2O2-chloramines AOP. Although radical production was higher from the UV/H2O2-chloramines AOP than the UV/H2O2 AOP, the UV/H2O2 AOP was at least two-fold more efficient for 1,4-dioxane degradation, because chloramines efficiently scavenged radicals. At low chloramine concentrations, the UV/chloramines AOP efficiency increased with increasing chloramine concentration, as radical production increased relative to radical scavenging by the dissolved organic carbon (DOC) in RO permeate. However, the efficiency leveled out at higher chloramine concentrations as radical scavenging by chloramines offset increased radical production. 1,4-Dioxane degradation was ~30-50% lower for the UV/chloramines AOP than the UV/H2O2-chloramines AOP when the residual chloramines in RO permeate were ~50 mM (3.3 mg/L as Cl2). Initial cost estimates indicate that the UV/chloramines AOP using the residual chloramines in RO permeate could be a cost-effective alternative to the current UV/H2O2-chloramines AOP in some cases, because the savings in reagent costs offset the ~30-50% reduction in 1,4-dioxane degradation efficiency.

Predicting the contribution of chloramines to contaminant decay during UV/hydrogen peroxide advanced oxidation process (AOP) treatment for potable reuse

2019 Fall National Meeting

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