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1. UV/Peracetic Acid for Degradation of Pharmaceuticals and Reactive Species Evaluation

   https://doi.org/https://doi.org/10.1021/acs.est.7b04694  

   Cai, M.; Sun, P.; Zhang, L.; Huang, C.-H. (January 2017, Environmental science & technology)

   Peracetic acid (PAA) is a widely used disinfectant, and combined UV light with PAA (i.e. UV/PAA) can be a novel advanced oxidation process for elimination of water contaminants. This study is among the first to evaluate the photolysis of PAA under UV irradiation (254 nm) and degradation of pharmaceuticals by UV/PAA. PAA exhibited high quantum yields (Φ254nm = 1.20 and 2.09 mol·Einstein−1 for the neutral (PAA0) and anionic (PAA-) species, respectively) and also showed scavenging effects on hydroxyl radicals (k•OH/PAA0 = (9.33±0.3)×108 M−1·s−1 and k•OH/PAA- = (9.97±2.3)×109 M−1·s−1). The pharmaceuticals were persistent with PAA alone but degraded rapidly by UV/PAA. The contributions of direct photolysis, hydroxyl radicals, and other radicals to pharmaceutical degradation under UV/PAA were systematically evaluated. Results revealed that •OH was the primary radical responsible for the degradation of carbamazepine and ibuprofen by UV/PAA, whereas CH3C(=O)O• and/or CH3C(=O)O2• contributed significantly to the degradation of naproxen and 2-naphthoxyacetic acid by UV/PAA in addition to •OH. The carbon-centered radicals generated from UV/PAA showed strong reactivity to oxidize certain naphthyl compounds. The new knowledge obtained in this study will facilitate further research and development of UV/PAA as a new degradation strategy for water contaminants. 

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2. Evaluation of parameters governing dark and photo-repair in UVC-irradiated Escherichia coli

   https://doi.org/10.1039/d1ew00644d  

   Maghsoodi, Mostafa; Lowry, Grace L.; Smith, Ian M.; Snow, Samuel D. (February 2022, Environmental Science: Water Research & Technology)

   After decades of UV disinfection practice and numerous studies on the potential for pathogens to undergo dark or photo-repair after UV exposure, recent advances in UV light emitting diode (LED) technologies prompt renewed attention to bacterial reactivation and regrowth processes after UV exposure. The aspect of photorepair conditions warrants particular attention, because even studies on conventional mercury vapor lamps have not sufficiently characterized these parameters. Wastewater encounters a wide range of environmental conditions upon discharge ( e.g. , solar irradiation and dissolved organics) which may affect repair processes and ultimately lead to overestimations of pathogen removal. Escherichia coli was used here to investigate the impacts of changing reactivation conditions after UV 254 and UV 278 irradiation. UV 254 and UV 278 doses of 13.75 ± 0.4 mJ cm −2 and 28.3 ± 0.8 mJ cm −2 were required to induce a 3.0 log inactivation of E. coli , respectively. Specifically, photoreactivation conditions were varied across dissolved organic matter (DOM) content and photoreactivation wavelengths and intensities. Photoreactivation achieved higher log recoveries than dark repair, ranging from 0.8 to 1.8 log differences, but a secondary disinfection effect occurred under UVA irradiation. During photoreactivation, humic acid inhibited the initial repair of UV 278 -dosed E. coli , but culture media enhanced recovery for both dosage wavelengths. Photoreactivation profiles under UV 395 , UV 365 , and visible light depended on both fluence and time, with more regrowth observed upon exposure to visible light and the least under 365 nm. The susceptibility of E. coli to UVA was increased by prior exposure to UVC. 

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3. Fecal coliform and E. coli in microplastic biofilms grown in wastewater and inactivation by peracetic acid

   https://doi.org/10.1002/wer.1434  

   Boni, William; Parrish, Kathleen; Patil, Shreya; Fahrenfeld, N.L. (August 2020, Water Environment Research)

   Microplastics (MP) have been proposed as a vector for pathogenic microorganisms in the freshwater environment. The objectives of this study were (1) to compare the fecal indicator growth in biofilms on MP and material control microparticles incubated in different wastewater fractions and (2) to compare MP biofilm, natural microparticle biofilm, and planktonic cell susceptibility to disinfection by peracetic acid (PAA). Biofilms were grown on high‐density polyethylene, low‐density polyethylene, polypropylene MP or wood chips (as a material control) and incubated in either wastewater influent or pre‐disinfection secondary effluent. Reactors were disinfected with PAA, biofilms were dislodged, and fecal coliform and E. coli were cultivated. Fecal indicators were quantifiable in both MP and wood biofilms incubated in the wastewater influent but only on the wood biofilms incubated in secondary wastewater effluent. More fecal coliform grew in the wood biofilms than MP biofilms, and the biofilms grown on MP and woodchips were more resistant to disinfection than planktonic bacteria. Thus, it may be possible to refer to the disinfection literature for fecal indicators in biofilm on other particles to predict behavior on MP. Treatments that remove particles in general would help reduce the potential for fecal indicator bypass of disinfection. 

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4. Oxidation of Amino Acids by Peracetic Acid: Reaction Kinetics, Pathways and Theoretical Calculations

   https://doi.org/https://doi.org/10.1016/j.wroa.2018.09.002  

   Du, P.; Liu, W.; Cao, H.; Zhao, H.; Huang, C.-H. (January 2018, Water research. X)

   Peracetic acid (PAA) is a sanitizer with increasing use in food, medical and water treatment industries. Amino acids are important components in targeted foods for PAA treatment and ubiquitous in natural waterbodies and wastewater effluents as the primary form of dissolved organic nitrogen. To better understand the possible reactions, this work investigated the reaction kinetics and transformation pathways of selected amino acids towards PAA. Experimental results demonstrated that most amino acids showed sluggish reactivity to PAA except cysteine (CYS), methionine (MET), and histidine (HIS). CYS showed the highest reactivity with a very rapid reaction rate. Reactions of MET and HIS with PAA followed second-order kinetics with rate constants of 4.6 ± 0.2, and 1.8 ± 0.1 M−1s−1 at pH 7, respectively. The reactions were faster at pH 5 and 7 than at pH 9 due to PAA speciation. Low concentrations of H2O2 coexistent with PAA contributed little to the oxidation of amino acids. The primary oxidation products of amino acids with PAA were [O] addition compounds on the reactive sites at thiol, thioether and imidazole groups. Theoretical calculations were applied to predict the reactivity and regioselectivity of PAA electrophilic attacks on amino acids and improved mechanistic understanding. As an oxidative disinfectant, the reaction of PAA with organics to form byproducts is inevitable; however, this study shows that PAA exhibits lower and more selective reactivity towards biomolecules such as amino acids than other common disinfectants, causing less concern of toxic disinfection byproducts. This attribute may allow greater stability and more targeted actions of PAA in various applications. 

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5. Elimination of transforming activity and gene degradation during UV and UV/H ₂ O ₂ treatment of plasmid-encoded antibiotic resistance genes

   https://doi.org/10.1039/c8ew00200b  

   Yoon, Younggun; Dodd, Michael C.; Lee, Yunho (January 2018, Environmental Science: Water Research & Technology)

   null (Ed.)

   To better understand the elimination of transforming activity of antibiotic resistance genes (ARGs), this study investigated the deactivation of transforming activity of an ARG (in Escherichia coli as a host) and ARG degradation (according to quantitative PCR [qPCR] with different amplicon sizes) during UV (254 nm) and UV/H 2 O 2 treatments of plasmid pUC19 containing an ampicillin resistance gene ( amp R ). The required UV fluence for each log 10 reduction of the transforming activity during UV treatment was ∼37 mJ cm −2 for both extra- and intra-cellular pUC19 (the latter within E. coli ). The resulting fluence-based rate constant ( k ) of ∼6.2 × 10 −2 cm 2 mJ −1 was comparable to the k determined previously for transforming activity loss of plasmids using host cells capable of DNA repair, but much lower (∼10-fold) than that for DNA repair-deficient cells. The k value for pUC19 transforming activity loss was similarly much lower than the k calculated for cyclobutane-pyrimidine dimer (CPD) formation in the entire plasmid. These results indicate the significant role of CPD repair in the host cells. The degradation rate constants ( k ) of amp R measured by qPCR increased with increasing target amplicon size (192–851 bp) and were close to the k calculated for the CPD formation in the given amplicons. Further analysis of the degradation kinetics of plasmid-encoded genes from this study and from the literature revealed that qPCR detected most UV-induced DNA damage. In the extracellular plasmid, DNA damage mechanisms other than CPD formation ( e.g. , base oxidation) were detectable by qPCR and gel electrophoresis, especially during UV/H 2 O 2 treatment. Nevertheless, the enhanced DNA damage for the extracellular plasmids did not result in faster elimination of the transforming activity. Our results indicate that calculated CPD formation rates and qPCR analyses are useful for predicting and/or measuring the rate of DNA damage and predicting the efficiency of transforming activity elimination for plasmid-encoded ARGs during UV-based water disinfection and oxidation processes. 

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