Demonstration-scale evaluation of ozone-biofiltration-granular activated carbon advanced water treatment for managed aquifer recharge

Pilot Assessment of Impacts of Ozone and Ozone/Hydrogen Peroxide Treatment on the Fate of Per- and Polyfluoroalkyl Substances and Precursors

Per- and polyfluoroalkyl substances (PFAS) make up a large class of anthropogenic micropollutants prevalent in wastewater. Oxidative processes commonly used in wastewater potable reuse treatment may affect transformation of PFAS precursors, leading to elevated concentrations of perfluorinated alkyl acids (PFAAs) that are significant health concerns. This work conducted a pilot-scale investigation to assess the influence of ozonation (O3) and ozone/hydrogen peroxide (O3/H2O2) advanced oxidation process (AOP), respectively, on the fate of PFAS in a wastewater effluent subjected to reuse. The study evaluated 40 target PFAS and associated precursors [based on the total oxidizable precursor (TOP) assay] under various treatment conditions, including different ozone doses (1.0-4.0 mg·L-1), H2O2 doses (0-0.20 mg·L-1), and contact time (0-20 min). Results indicated that short-chain (C3-C7) PFAAs dominated in concentrations, while overall PFAA concentrations were elevated by both oxidative treatment processes, particularly after high-dose ozonation treatment. TOP assays revealed that there were considerable amounts of PFAA precursors in the reuse wastewater, and their concentrations were decreased after the oxidative treatment with an increase of some of the PFAAs. This pilot study demonstrated that ozone and ozone-based AOP treatments can have a moderate influence on the transformation of PFAS and increase in PFAA levels under practical conditions.

Optimizing Ozone Disinfection in Water Reuse: Controlling Bromate Formation and Enhancing Trace Organic Contaminant Oxidation

The use of ozone/biofiltration advanced treatment has become more prevalent in recent years, with many utilities seeking an alternative to membrane/RO based treatment for water reuse. Ensuring efficient pathogen reduction while controlling disinfection byproducts and maximizing oxidation of trace organic contaminants remains a major barrier to implementing ozone in reuse applications. Navigating these challenges is imperative in order to allow for the more widespread application of ozonation. Here, we demonstrate the effectiveness of ozone for virus, coliform bacteria, and spore forming bacteria inactivation in unfiltered secondary effluent, all the while controlling the disinfection byproduct bromate. A greater than 6-log reduction of both male specific and somatic coliphages was seen at specific ozone doses as low as 0.75 O3:TOC. This study compared monochloramine and hydrogen peroxide as chemical bromate control measures in high bromide water (Br- = 0.35 ± 0.07 mg/L). On average, monochloramine and hydrogen peroxide resulted in an 80% and 36% decrease of bromate formation, respectively. Neither bromate control method had any appreciable impact on virus or coliform bacteria disinfection by ozone; however, the use of hydrogen peroxide would require a non-Ct disinfection framework. Maintaining ozone residual was shown to be critical for achieving disinfection of more resilient microorganisms, such as spore forming bacteria. While extremely effective at controlling bromate, monochloramine was shown to inhibit TrOC oxidation, whereas hydrogen peroxide enhanced TrOC oxidation.

In vitro bioassays to monitor complex chemical mixtures at a carbon-based indirect potable reuse plant

Potable water reuse technologies are used to treat wastewater to drinking water quality to help sustain a community's water resources. California has long led the adoption of potable water reuse technologies in the United States and more states are exploring these technologies as water resources decline. Reuse technologies also need to achieve adequate reductions in microbial and chemical contaminant risks to meet public health goals and secure public acceptance. In vitro bioassays are a useful tool for screening if reuse treatment processes adequately reduce toxicity associated with a range of chemical classes that are contaminants of concern. In this study, we used an aryl hydrocarbon receptor (AhR) and an estrogen receptor luciferase bioassay to detect the presence of dioxin-like and estrogenic compounds across a 3800 m³/d carbon-based indirect potable reuse plant that uses carbon-based treatment (SWIFT-RC). Our results demonstrate significant removal of dioxin-like compounds across the SWIFT-RC treatment train. Estrogenicity declined across the treatment train for some months but was extremely variable and low with many samples falling below the method quantification level; consequently, we were not able to reliably determine estrogenicity trends for SWIFT-RC. Comparing the bioanalytical equivalent concentrations detected in the SWIFT-RC water with established monitoring trigger levels from the state of California suggests that SWIFT-RC produced water that met the bioassay guidelines. The log total organic carbon concentration and AhR assay equivalent concentrations are weakly correlated when data across all SWIFT-RC processes are included. Overall, this research demonstrates the performance of in vitro bioassays at a demonstration-scale carbon-based IPR system and highlights both the potential utility and challenges associated with these methods for assessing system performance.

Electron beam treatment for the removal of 1,4-dioxane in water and wastewater

Electron beam (e-beam) treatment uses accelerated electrons to form oxidizing and reducing radicals when applied to water without the use of external chemicals. In this study, electron beam treatment was used to degrade 1,4-dioxane in several water matrices. Removal improved in the progressively cleaner water matrices and removals as high as 94% to 99% were observed at a dose of 2.3 kGy in secondary effluent. 1,4-dioxane removal was confirmed to be primarily through hydroxyl radical oxidation. The calculated electrical energy per order was found to be 0.53, 0.26, and 0.08 kWh/m³/order for secondary effluent (Avg. total organic carbon (TOC) 9.25 mg/L), granular activated carbon effluent (TOC 3.46 mg/L), and ultrapure water, respectively, with a 70% generation and transfer efficiency applied.