Enhancing Efficiency of Uv Advanced Oxidation Processes Via Iron Addition

Ulliman, Sydney L.

Graduate Thesis Or Dissertation

Enhancing Efficiency of Uv Advanced Oxidation Processes Via Iron Addition Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/z316q202p

Abstract

Advanced oxidation processes (AOPs) have been recognized as a treatment technology to effectively remove a wide range of organic compounds in wastewater. Among different AOP methods, ultraviolet irradiation with hydrogen peroxide (UV/H₂O₂) is one of the leading technologies currently employed in numerous water treatment projects. Iron-assisted UV/H₂O₂, an alternative UV/AOP technology which uses photo-Fenton reactions (UV + H₂O₂ + iron) to increase hydroxyl radical production, has been used to effectively reduce organics at circumneutral pH; however, previous studies have evaluated iron-assisted UV/H₂O₂ systems using of high iron (>0.3 mg/L) and hydrogen peroxide concentrations (>10 mg/L) for wastewater treatment applications.

The goal of the present study was to evaluate the enhanced oxidation potential of iron-assisted UV/H₂O₂ using iron levels below USEPA secondary drinking water standards (0 to 0.3 mg/L). Chemically and kinetically diverse compounds para-chlorobenzoic acid (pCBA), carbamazepine (CBZ), and n-nitrosodimethylamine (NDMA) were selected to assess if low-levels of iron increased chemical degradation, and subsequently observe chemical-specific responses to iron-enhanced UV/H₂O₂ treatment. A quasi-collimated low-pressure UV device was used to expose low-carbon tap water (LCT) and well water samples to UV only, and samples dosed with 5 and 10 mg/L hydrogen peroxide and incremental ferrous and ferric iron levels typical of well waters. Steady-state hydroxyl radical (HO·) production was determined using radical probe pCBA. Degradation rate constants were experimentally determined for all test scenarios and compared against modeled results.

Iron-assisted UV/H₂O₂ efficiency at neutral pH was shown to be most influenced by photochemical and kinetic properties of the target chemical and the water matrix. Contrary to previous studies using higher levels of iron and H₂O₂ (>10 mg/L), chemical removal rates were not impacted by iron species, iron concentration or H₂O₂ concentration. With the exception of NDMA, chemical degradation was not improved in LCT water for iron-assisted UV/H₂O₂ scenarios presumably due to the absence of organic and inorganic ligands. For iron-assisted UV/H₂O₂ tests conducted in well water, a 20% increase in HO˙ production was observed as measured by the radical probe pCBA, and NDMA degradation rates increased by 14% to 24%. CBZ removal was neither improved or inhibited by the presence of iron. Interestingly, NDMA was the only chemical where iron addition increased removal rates in LCT and well water. Furthermore, iron without H₂O₂ addition was shown to enhance NDMA removal by 38% in LCT water and 8% in well water when compared to UV photolysis alone.

This work provides an understanding of the fundamental role of iron in a UV/H₂O₂ systems, provides a basis for improved modeling of AOPs in the presence of iron, and could indicate a strategy for improving the efficiency of UV/AOP treatment.

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