Applying UV absorbance and fluorescence indices to estimate inactivation of bacteria and formation of bromate during ozonation of water and wastewater effluent

Abstract

Ozone is an effective oxidant and disinfectant commonly used for elimination of micropollutants and inactivation of resistant microbes. However, undesirable oxidation/disinfection byproducts such as bromate might form during ozonation. In this study, the UV absorbance and fluorescence indices were applied as surrogate indicators for predicting the inactivation of bacteria and formation of bromate during ozonation of water and wastewater effluents. The inactivation efficiencies of lab-cultured Escherichia coli (E. coli) and autochthonous bacteria were measured by plating (for E. coli only) and flow cytometry with fluorescence staining. During ozonation of E. coli spiked into wastewater effluents (∼10 cell/mL), the priority of inactivation efficiency determined by different cell viability methods were in the order of CFU > membrane damage > DNA damage. Approximately, 99% membrane damage and/or 90% DNA damage are conservatively supposed as an indicator for sufficient bacterial inactivation as well as degradation of antibiotic resistance genes. The related required O dosing thresholds for sufficient inactivation of E. coli and autochthonous bacteria refer to ∼0.6 O/DOC (g/g), ∼50% decrease of UVA254, ∼60% decrease of UVA280, or ∼80% decrease of humic-like fluorescence. Within the range of 10-10 cell/mL, the bacterial concentration did not have significant effects on the required thresholds of the specific O doses or spectroscopic indicators required for bacterial inactivation. The addition of 50 mM tert-BuOH as ·OH scavenger increased the required specific ozone doses but decreased the losses of spectroscopic indicators necessary for sufficient bacterial inactivation, and also suggested that the membrane/DNA damages for bacterial inactivation were mainly attributed to the direct O attacks. The bromate concentration was determined using ion chromatography with MS/MS detection. The results showed that when O was dosed at the required thresholds for sufficient bacterial inactivation, bromate formation could usually be suppressed below 10 μg/L. The present work supports that it is possible to reach a balance between bacterial inactivation and bromate formation.

Trace and bulk organics removal during ozone–biofiltration treatment for potable reuse applications

“…Therefore, dissolved ozone residual is often not a reliable parameter for real‐time control. Several researchers have investigated the potential of utilizing UVA 254 or UVT 254 for real‐time monitoring and control of ozonation systems (Wert et al ; Chys et al, ; Wu et al, ). Trends observed in the field confirmed that the UVA decrease or UVT increase is proportional to ozone dose or ozone:TOC ratio.…”

“…Advantages of utilizing UVA 254 or UVT 254 for ozonation process control are (a) UVA or UVT is expected to change with ozone dose or ozone:TOC ratio, and (b) online monitoring is available and more feasible than fluorescence and other methods. Investigators have attempted to correlate %UVA to CEC removal, DNA damage (as a measure of pathogen inactivation and bromate formation), and CEC and bulk organics removal (Chys et al, ; Wu et al, ). Because each study or project has had a specific ozone dose and process control strategy, applications of those correlations have been limited.…”

Investigation of reduction in risk from antibiotic resistance genes in laboratory wastewater by using O3, ultrasound, and autoclaving

“…Ozone is an effective disinfectant that can be used for the inactivation of microbes, including resistant bacteria (Wu et al, 2018). Ultrasonic treatment can also be used to eliminate bacteria (Sarkinas et al, 2018).…”

Developing surrogate indicators for predicting suppression of halophenols formation potential and abatement of estrogenic activity during ozonation of water and wastewater

“…A number of indicators deemed to be suitable for optimizing ozone doses have been proposed. These are based on O 3 /DOC (dissolved organic carbon) mass ratio, differential UV absorbance (e.g., ΔUVA254 & UVA280), differential total/component fluorescence (e.g., ΔTF) and electron donating capacity (Chon et al, 2015;Gerrity et al, 2012;Li et al 2016Li et al , 2017Wu et al, 2018). For online measurements, UV absorbance and fluorescence indices are most applicable, since miniaturized UV absorbance and fluorescence spectroscopy prototypes and deployment-ready devices that use UV light emitting diode have been developed (Li et al, 2016;Tedetti et al, 2013).…”