Groundwater resources worldwide are contaminated with numerous chemicals including volatile organics, pesticides, and hazardous substances that pose risks to human health and ecology. Advanced oxidation processes (AOPs) particularly sulfate radical based advanced oxidation processes (SR-AOPs) has several advantages over hydroxyl radical based advanced oxidation processes (HR-AOPs) including a wider operational pH range, longer half-life of SO₄^.- (30-40 µs vs. 20 ns of HO^.), and high redox potential at circumneutral pH. There is also evidence that SR-AOPs can be more effective than HR-AOPs, but there is a need for thorough comparison of these two radicals. There is also need to leverage computational tools for insights into their mechanistic differences. The objective of this study was to compare HR and SR-based AOPs using laboratory studies and computational analyses. This study utilized Methyl Tert-Butyl Ether (MTBE) and Tert-Butyl Alcohol (TBA), two well-documented examples of groundwater pollutants. Experiments were conducted with 7.4 mg/L MTBE and 6.2 mg/L TBA at molar peroxide ratios of 50:1, 100:1, 250:1, and 500:1 with UV/H₂O₂ (HR-AOP) and UV/Persulfate (SR-AOP). SR-AOPs removed both chemicals faster than HR-AOP. Pseudo first-order kinetic constants for MTBE were 0.026 min^-1 & 0.41 min^-1for HR-AOP & SR-AOP respectively; for TBA they were TBA 0.024 min^-1 & 0.16 min^-1 respectively. More than 90% of MTBE and 60% of TBA was removed using UV/Persulfate; however with UV/H₂O₂ removal was < 30%. Activation energies for TBA transformation was greater than that of MTBE. This finding is consistent with experimental results that show that TBA reaction kinetics to be slower than that of MTBE.

Advanced oxidation of MTBE and TBA with UV/H<sub>2</sub>O<sub>2 </sub>and UV/Persulfate.

Advanced oxidation of MTBE and TBA with UV/H₂O₂and UV/Persulfate.

Graphical abstract

Willie Harper

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