Understanding the similarities and differences between ozone and peroxone in the degradation of naphthenic acids: Comparative performance for potential treatment

- Molecular ozone pathway was responsible for degrading around 40-50% of the O2-NA.
- |-Z|≥10 isomers in ozone treatments were significantly degraded by molecular O3.
- Structure reactivity is related individually to n and Z and their combined effect.
- Peroxone ratio's effectiveness: (1:2) for degradation vs (1:1) for oxidant utilization.
- At n = 9-11; peroxone (1:1) achieved similar or better degradation than 50 mg/L O3.

Ozonation at high doses is a costly treatment for oil sands process-affected water (OSPW) naphthenic acids (NAs) degradation. To decrease costs and limit doses, different peroxone (hydrogen peroxide/ozone; H2O2:O3) processes using mild-ozone doses of 30 and 50 mg/L were investigated. The degradation efficiency of Ox-NAs (classical (O2-NAs) + oxidized NAs) improved from 58% at 30 mg/L ozone to 59%, 63% and 76% at peroxone (1:1), 50 mg/L ozone, and peroxone (1:2), respectively. Suppressing the hydroxyl radical (
- OH) pathway by adding tert-butyl alcohol did significantly reduce the degradation in all treatments, while molecular ozone contribution was around 50% and 34% for O2-NAs and Ox-NAs, respectively. Structure reactivity toward degradation was observed with degradation increase for both O2-NAs and Ox-NAs with increase of both carbon (n) and hydrogen deficiency/or |-Z| numbers in all treatments. However, the combined effect of n and Z showed specific insights and differences between ozone and peroxone treatments. The degradation pathway for |-Z|≥10 isomers in ozone treatments through molecular ozone was significant compared to
- OH. Though peroxone (1:2) highly reduced the fluorophore organics and toxicity to Vibrio fischeri, the best oxidant utilization in the degradation of O2-NAs (mg/L) per ozone dose (mg/L) was observed in the peroxone (1:1) (0.91) and 30 mg/L ozone treatments (0.92). At n = 9-11, peroxone (1:1) had similar or enhanced effect on the O2-NAs degradation compared to 50 mg/L ozone. Enhancing
- OH pathway through peroxone versus ozone may be an effective OSPW treatment that will allow its safe release into receiving environments with marginal cost addition.

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