Robustness of a demonstration potable reuse facility was evaluated through a series of system-wide chemical challenge tests spiking neutral low-molecular weight compounds (acetone, formaldehyde, N-nitrosodimethylamine (NDMA), and 1,4-dioxane) which are known to be challenging for removal through advanced treatment. Two advanced treatment train arrangements were compared: O3/BAC-MF/UF-RO-AOP and RO-AOP. Ozone and biological activated carbon (O3/BAC) offered significant attenuation of the smallest and most biologically degradable compounds tested: acetone and formaldehyde. These two compounds had limited reduction across the reverse osmosis (RO) membrane barrier and the different advanced oxidation process (AOP) setups used. 1,4-Dioxane was partially reduced across the oxidation barriers: 62% across ozonation and up to 95% across AOP depending on oxidant used and oxidant dose. Both a hydrogen peroxide (H2O2) based AOP (UV/H2O2) and a sodium hypochlorite (as HOCl) based AOP (UV/HOCl) demonstrated sufficient oxidation, providing no less than 0.5-log (68%) 1,4-dioxane attenuation required by regulators in the USA. NDMA was reduced across both UV/H2O2 and UV/HOCl from 157 to 267 ng/L to below the 10 ng/L established notification level for drinking water in California. Overall, addition of O3/BAC enhanced cumulative removal of all the spiked trace organic chemicals, providing greater protection against the spiked contaminants than RO-AOP alone. In addition, online total organic carbon (TOC) monitoring successfully captured the presence of the spiked chemicals.

The mechanical reliability of a direct potable reuse (DPR) treatment train-consisting of ozone, biological activated carbon, microfiltration/ultrafiltration, reverse osmosis, and ultraviolet light with advanced oxidation-was evaluated using critical component analysis at the Demonstration Pure Water Facility in San Diego, Calif. Operators maintained logs of all mechanical issues that occurred over a yearlong test period; these were used to calculate several reliability metrics for the unit processes. Mechanical issues were also cross-referenced with treatment performance data to determine whether any "critical" failures-i.e., those that impacted pathogen reduction performanceoccurred. The results demonstrated that no critical failures occurred, though the communication systems experienced critical malfunctions. These malfunctions triggered an immediate system shutdown, mitigating the potential risk to public health. While several components experienced failures, malfunctions, and/or maintenance events, the processes maintained a high degree of availability, demonstrating that DPR facilities can be designed with a high degree of mechanical reliability.

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