UV-based Advanced Oxidation Processes Research Articles

Far-UVC Photolysis of Peroxydisulfate for Micropollutant Degradation in Water.

Increasing radical yields to reduce UV fluence requirement for achieving targeted removal of micropollutants in water would make UV-based advanced oxidation processes (AOPs) less energy demanding in the context of United Nations' Sustainable Development Goals and carbon neutrality. We herein demonstrate that, by switching the UV radiation source from conventional low-pressure UV at 254 nm (UV254) to emerging Far-UVC at 222 nm (UV222), the fluence-based concentration of HO• in the UV/peroxydisulfate (UV/PDS) AOP increases by 6.40, 2.89, and 6.00 times in deionized water, tap water, and surface water, respectively, with increases in the fluence-based concentration of SO4•- also by 5.06, 5.81, and 55.47 times, respectively. The enhancement to radical generation is confirmed using a kinetic model. The pseudo-first-order degradation rate constants of 16 micropollutants by the UV222/PDS AOP in surface water are predicted to be 1.94-13.71 times higher than those by the UV254/PDS AOP. Among the tested water matrix components, chloride and nitrate decrease SO4•- but increase HO• concentration in the UV222/PDS AOP. Compared to the UV254/PDS AOP, the UV222/PDS AOP decreases the formation potentials of carbonaceous disinfection byproducts (DBPs) but increases the formation potentials of nitrogenous DBPs.

Development of dissolved organic matter-based indicators to understand the degradation of organic contaminants in reverse osmosis concentrate from potable reuse systems

Reverse osmosis (RO)-based treatment of municipal wastewater effluent allows for potable reuse, but this process generates reverse osmosis concentrate (ROC) that needs further treatment before disposal. This study investigated the application of UV-based advanced oxidation processes (AOPs) to degrade nine contaminants of emerging concern (CECs) from real ROC waste streams, using UV-only and UV-AOPs with hydrogen peroxide, free chlorine, and persulfate. Dissolved organic matter (DOM) in ROC was characterized using fluorescence excitation emission matrix data and analyzed by a four-component parallel factor (PARAFAC) analysis model. UV-only treatment showed considerable removal of CECs that displayed high values of quantum yields and molar absorption coefficients. UV-AOP treatment of ROC exhibited heavy scavenging of reactive species during CEC degradation. A probe-based approach established that hydroxyl radical was the dominant reactive species in all UV-AOPs. A kinetic analysis of PARAFAC components of DOM showed that the visible humic-like and protein-like components exhibited the higher reaction kinetics compared to UV humic-like and nutrient-like components. The strong linear correlation of protein-like component and seven of the nine CECs across multiple AOPs indicated that they have similar reactivity, enabling the establishment of chemical-reactivity based surrogates for prediction CEC fate in ROC wastes.

Nitrogen-reliant degradation behaviors of characteristic NHCs by UV-based advanced oxidation processes: Kinetics, pathways and toxicity assessment

In recent decades, nitrogen-containing heterocyclic compounds (NHCs) have been widely synthesized and applied due to their excellent coordination capability of heterocyclic N atoms. However, their high toxicity and poor biodegradability pose significant hazards to aquatic ecosystems. Three characteristic NHCs (cNHCs) with similar molecular structures but minor differences in the number and position of N atoms, namely benzotriazole (BTA), benzimidazole (BMZ), and indazole (IDZ), were selected to evaluate impacts of these differences on their degradation behaviors during UV/H2O2 treatments. It was found that the key mechanism for the removal of BTA, BMZ, and IDZ in the UV/H2O2 processes was the generation of ∙OH through UV-excited H2O2 decomposition. Density functional theory (DFT) calculations revealed that the variation in the number and position of heterocyclic ring N atoms significantly affected the electron cloud distribution of the cNHCs, thereby resulting in different reactivities. Mineralization results and N evolution experiments indicated that N elements were initially released in the form of ammonia nitrogen during UV/H2O2 treatments, which then underwent oxidation to form nitrite and nitrate. The two ortho-N atoms were most easily mineralized and release inorganic nitrogen, followed by the two meta-N atoms. However, the BTA compound containing three N atoms, exhibited inertness towards radicals after hydroxylation, thereby hindering mineralization. A dual-directional transformation products (TPs) identification protocol was employed to identify 30 TPs of the cNHCs and propose recommended degradation pathways. Furthermore, Vibrio fischeri bioluminescence inhibition bioassay and QSAR prediction models were used to preliminarily screen and identify 13 toxic TPs with potential ecological risks.

Elucidating the performance of UV-based photochemical processes for the removal of trace organic contaminants: Degradation and toxicity evaluation

In this study, the performance of standalone ultraviolet (UV) photolysis and UV-based advanced oxidation processes (AOPs), namely, UV/hydrogen peroxide, UV/chlorine, UV/persulphate, and UV/permonosulphate, were investigated for the degradation of 31 trace organic contaminants (TrOCs). Under the tested conditions, standalone UV photolysis did not achieve effective removal of TrOCs. To improve the degradation efficiency of UV photolysis, four different oxidants were added individually to the test solution. The effect of these oxidants in the absence of UV irradiation was also explored and only chlorine showed promising degradation of some contaminants. During the chlorination of 31 investigated TrOCs, only six demonstrated greater than 50% degradation. The combined UV-based AOPs demonstrated much improved degradation (ranging from 65 to 100%) depending on TrOC-structure and oxidant concentration. The UV/hydrogen peroxide process showed similar degradation of TrOCs, irrespective of the functional groups (i.e., electron withdrawing groups, EWGs and electron donating groups, EDGs) present in their structures. Conversely, the UV/sulphate and UV/chlorine based processes achieved better degradation of the TrOCs with EDGs in their structures. TrOCs degradation improved up to 40% when oxidants concentrations were increased from 0.1 to 1 mM, and further increasing the concentration to 2 mM did not improve degradation. Toxicity evaluation using bioluminescence test (BLT assay) demonstrated that except for UV/hydrogen peroxide, all UV-based AOPs increased the toxicity of the treated effluent, indicating generation of toxic by-products. This study elucidates the performance of four different UV-based AOPs for the removal of commonly detected diverse TrOCs for the first time.

The various effects of hydrogen phosphate and bicarbonate in the degradation of some pollutants in the UV/chlorine and the UV/H2O2 processes

In this study, the degradation kinetics of three target pollutants (i.e., levofloxacin (LEV), P-nitrosodimethylaniline (RNO), and basic fuchsin (BF) in four UV-based Advanced Oxidation Processes (UV/AOPs) (i.e., UV/NaOCl/HPO42−, UV/NaOCl/HCO3−, UV/H2O2/HPO42−, and UV/H2O2/HCO3−) were comprehensively investigated. The results showed that LEV and RNO were resistant to UV irradiation, chlorination, and H2O2 when applied separately, but significantly degraded in UV/AOPs. The chlorination process and alkaline conditions were beneficial to the degradation of BF. In UV/AOPs, the degradation rates of the pollutants were enhanced remarkably with different rate constants which were dependent on the dosage of oxidants, and the presence of HPO42− and HCO3−. This enhancement is due to the generation of reactive species (i.e., •OH, RCS, and secondary reactive radicals like PO42•-, and CO3•-). The study also investigated the role and contribution of the reactive species to the degradation of the pollutants in UV/AOPs. The study demonstrated the difference in the degradation kinetics of the pollutants in UV/H2O2/(HPO42− or HCO3−) and UV/NaOCl/(HPO42− or HCO3−) in which the contribution of each oxidizing factor was determined. Acidic conditions were beneficial to the degradation rate of the pollutants in all UV/AOPs, except BF in UV/NaOCl. Seawater and river water were demonstrated to significantly promote the degradation rate of pollutants in UV/NaOCl/(HPO42− or HCO3−) but depressed it in UV/H2O2/(HPO42− or HCO3−). In addition, a typical PPCP (pharmaceutical and personal care product) (here LEV) was selected for further LC-MS analysis to determine its degradation pathway. The results provide a novel alternative strategy in the use of HPO42− and HCO3− in UV/NaOCl and UV/H2O2 to increase the removal efficiency of organic pollutants.

Spectroscopic analysis on effluent organic matter (EfOM) evolution in different UV-based advanced oxidation processes

The effluent organic matter (EfOM) removal performance of the advanced wastewater treatment process has drawn great attention owing to the potential ecological risk of EfOM in the receiving aquatic environments. However, the EfOM evolution process is still unclear in the various advanced wastewater treatment processes. In this study, the EfOM evolution process in terms of components, structures, and functional groups was investigated in four kinds of UV-based advanced oxidation processes (AOPs). The overall EfOM removal performances were in the order: UV/NaClO > UV/PMS > UV/H2O2 > UV. According to the spectroscopic analysis results, simple aliphatics/aromatic/acetylenes compounds with C–O, =C–H, amides, or amino structures deriving from protein-like substances, are easily destroyed under UV irradiation. Apart from these structures, microbial metabolic was strongly sensitive to a reactive chlorine species (RCS)-dominated system, especially nutrients, amino acids, and small peptides with ester. Total of 22 species of halogen by-products with high biotoxicity (acetonitrile-based chlorinated EfOM, chlorinated acetate, chlorinated methane) were detected in the UV/NaClO group. In contrast, the reactive oxygen species (ROS)-dominated systems exhibited strong structure selectivity for ester (UV/H2O2) and carbonyl (UV/PMS) in all of the EfOM components, exhibiting strong reaction activity with EfOM at different stages. The results reveal the EfOM evolution in different UV-based AOPs, providing a strategy for selecting suitable UV-based AOPs in the advanced wastewater treatment process in terms of high-efficiency removal of EfOM.

Promoting multiple reactive oxygen species generation for deep oxidation of VOCs by UV/persulfate/permanganate

Advanced oxidation processes (AOPs) could effectively remove volatile organic compounds (VOCs) when coupled with wet scrubbing process. However, it still faces challenges in achieving deep oxidation of VOCs due to the limited production of reactive oxygen species (ROS). Herein, we present the utilization of permanganate (KMnO4) as a co-oxidant to enhance VOCs oxidation in UV/persulfate (PDS)/KMnO4 system. The removal efficiency of a targeted VOC, toluene, kept high at above 90% throughout the entire long-term reaction of 4 h, which was much higher than that of UV/PDS and UV/KMnO4. Notably, the in-situ formed manganese oxide (MnOx) acts as a catalyst in UV/MnOx and UV/MnOx/PDS, facilitating the generation of various ROS and thereby enhancing VOCs degradation. Electron paramagnetic resonance (EPR) and quenching experiments indicated that sulfate radical (SO4−), hydroxyl radical (HO), superoxide radical (O2−) and singlet oxygen (1O2) were the main ROS generated in the UV/PDS/KMnO4 system. The overall oxidation process can be divided into three stages: the UV/KMnO4-dominated stage, the UV/MnOx/PDS-dominated stage, and the UV/MnOx-dominated stage. Correspondingly, HO played a major role in toluene oxidation in the UV/KMnO4-dominated and UV/MnOx-dominated stages, with the contributions of 48% and 52%, respectively. Meanwhile, SO4− played a more significant role in the UV/MnOx/PDS-dominated stage, with a contribution of 59%. Three main reaction pathways involving electron abstraction, HO addition and benzene ring opening were proposed based on the intermediates identified by proton-transfer-reaction mass spectrometry (PTR-MS). This study provided a deep understanding of KMnO4 in improving the oxidation capacity of UV-based AOPs for VOCs degradation, emphasizing the importance of in-situ formed MnOx for promoting multiple ROS generation.

UV-based advanced oxidation processes in photoreactors with reflective sleeves

UV-based advanced oxidation processes (UV-based AOPs) via photolysis of radical precursor chemicals (RPCs) are among the most effective technologies for eliminating trace organic contaminants in water treatment facilities. However, mathematical discussions on the kinetics and energy consumption for the engineering photoreactor set-up of UV-based AOPs, especially the newly proposed UV-based AOPs (e.g., UV/persulfate, UV/chlorine and UV/chloramine), are scarce. In this study, a photoreactor with reflective sleeves was mathematically characterized and validated using clean and complex water matrices, and approaches for measuring effective light absorbance by RPC (IRPC) and the reflectance of the photoreactor wall (η) were proposed. By applying IRPC and η, and employing geosmin as a model compound, energy optimization of the UV-based AOPs was conducted based on an updated kinetic model. A new equation was derived for UV/H2O2 to obtain the most cost-effective RPC dose regarding EE/O (electric energy required for one order of contaminant removal) (Copt-EE/O). This equation was then successfully extended to other UV-based AOPs (including UV/persulfate, UV/chlorine, and UV/chloramine). The balance between the treatment goals and operational costs was also discussed. Overall, the new concepts and approaches proposed in this study may aid in the energy optimization and reduce RPC consumption of various UV-based AOPs for engineering applications.

Degradation of 75 organic micropollutants in fresh human urine and water by UV advanced oxidation process

In household wastewater, a large proportion of organic micropollutants (OMPs) load is attributed to human urine. OMPs could pose a risk to human and environmental health when urine collected in source-separating sanitation systems is recycled as crop fertiliser. This study evaluated degradation of 75 OMPs in human urine treated by a UV-based advanced oxidation process. Fresh urine and water samples were spiked with a broad range of OMPs and fed into a photoreactor equipped with a UV lamp (185 and 254nm) that generated free radicals in situ. Degradation rate constant and the energy required to degrade 90% of all the OMPs in both matrices were determined. At a UV dose of 2060J m-2, average ΣOMP degradation of 99% (±4%) in water and 55% (±36%) in fresh urine was achieved. The energy demand for removal of OMPs in water was <1500J m-2, but for removal of OMPs in urine at least 10-fold more energy was needed. A combination of photolysis and photo-oxidation can explain the degradation of OMPs during UV treatment. Organic substances (e.g. urea, creatinine) likely inhibited degradation of OMPs in urine by competitively absorbing UV-light and scavenging free radicals. There was no reduction in the nitrogen content of urine during treatment. In summary, UV treatment can reduce the load of OMPs to urine recycling sanitation systems.

Combination of H2O2-producing microbial desalination cells and UV/H2O2 advanced oxidation process: Water salinity reduction and microbial inactivation

Microbial desalination cells (MDCs) are bioelectrochemical devices that can recover usable energy and chemicals from organic wastes and concurrently desalinate saltwater. MDCs can also produce the green oxidant, H2O2, through a two-electron oxygen reduction reaction occurring on the cathode electrode. If MDCs producing H2O2 are used in the pretreatment of brackish water or seawater for reverse osmosis (RO) processes, the salinity of feed water can be reduced in MDCs and the MDC-produced H2O2 can be utilized onsite to oxidize organic contaminants or disinfect microorganisms in the feed water. This strategy of using MDC pretreatment may substantially alleviate the energy requirements and biofouling tendency of downstream RO units. Herein, we assessed the applicability of a combination of H2O2-producing MDCs and ultraviolet (UV) or UV254nn -based advanced oxidation process (AOP) (i.e., UV/H2O2) as pretreatment for RO processes. We first examined the effect of catholyte conditions, which is one of the most crucial factors directly affecting the H2O2 composition and decomposition, on the performance of MDCs. Then, we evaluated the microorganism disinfection efficiencies of advanced photo-oxidation processes using H2O2 obtained from MDCs. The MDC investigated herein achieved 93.1% desalination efficiency and > 5.0 mM H2O2 concentration. In addition, UV-based AOP with the produced H2O2 demonstrated up to 15-fold higher inactivation kinetics than that by UV254 nm disinfection alone.

Roles of radical species in vacuum-UV/UV/peroxydisulfate advanced oxidation processes and contributions of the species to contaminant degradation at different water depths

Vacuum-UV (VUV) (wavelength 185 nm)/ UV (wavelength 254 nm) are applied to improve performances of UV-based advanced oxidation processes. However, the improvements were strongly affected by water depth because of poor VUV transmittance in water. In this study, VUV/UV and peroxydisulfate (PDS) were used to degrade carbamazepine. More SO4•− oxidation occurred in VUV/UV/PDS than VUV/UV with similar •OH oxidation occurring. The additional SO4•− oxidation could be caused by VUV/PDS in superficial water or UV/PDS in deeper water. The synergistic factor for VUV/UV/PDS processes relative to VUV/UV and UV/PDS processes was 1.32. VUV/UV/PDS performances were affected by competition for photon absorption by dissolved organic matter (32–58 % inhibition), radical quenching by CO32−/HCO3− and NO3−, and conversion of •OH and SO4•− into reactive chlorine species by Cl−. Radical probe experiments and steady-state kinetic modeling simulations indicated that 34 %, 25 %, and 40 % of carbamazepine degradation occurring in 2-cm-deep bulk solution was due to •OH oxidation through VUV/H2O, SO4•− oxidation through VUV/PDS, and SO4•− oxidation through UV/PDS, respectively. Contribution of VUV-driven processes decreased with increasing water depth and became equivalent to contribution of 3.5-cm-deep UV-driven processes, which indicated the importance of optimizing water depth in VUV/UV-advanced oxidation process reactors.

A novel approach to interpret quasi-collimated beam results to support design and scale-up of vacuum UV based AOPs

UV-C at 254 nm and vacuum UV (VUV) at 185 nm are the two major emission lines of a low-pressure mercury lamp. Upon absorption of VUV photons, water molecules and selected inorganic anions generate hydroxyl (HO.) and other redox radicals, both capable of degrading organic micropollutants (OMPs), thereby offering the opportunity to reduce H2O2 and energy consumption in UV-based advanced oxidation process (AOP). To be successfully scaled-up, the dual-wavelength VUV+UV/H2O2 AOP requires laboratory-scale experiments to establish design criteria. The figures of merit typically used for reporting and interpreting quasi-collimated beam results for UV-based AOPs (time, dose, absorbed energy and EEO) are insufficient and inaccurate when employed for dual-wavelength AOP such as the VUV+UV/H2O2 AOP, and do not support system scale-up. In this study, we introduce a novel figure of merit, useful absorbed energy (uAE), defined as fraction of absorbed energy that results in the generation of oxidative radicals. Here, results of quasi-collimated beam VUV+UV/H2O2 AOP experiments on four different water matrices are used to introduce 2D plots that employ both uAEUV and uAEVUV as a novel method to represent laboratory-scale experiments of VUV+UV/H2O2 AOP and demonstrate how the 2D plots sufficiently support scale-up of the AOP.

Degradation of Antibiotics via UV-Activated Peroxodisulfate or Peroxymonosulfate: A Review

The ultraviolet (UV)/H2O2, UV/O3, UV/peroxodisulfate (PDS) and UV/peroxymonosulfate (PMS) methods are called UV-based advanced oxidation processes. In the UV/H2O2 and UV/O3 processes, the free radicals generated are hydroxyl radicals (•OH), while in the UV/PDS and UV/PMS processes, sulfate radicals (SO4•−) predominate, accompanied by •OH. SO4•− are considered to be more advantageous than •OH in degrading organic substances, so the researches on activation of PDS and PMS have become a hot spot in recent years. Especially the utilization of UV-activated PDS and PMS in removing antibiotics in water has received much attention. Some influencing factors and mechanisms are constantly investigated and discussed in the UV/PDS and UV/PMS systems toward antibiotics degradation. However, a systematic review about UV/PDS and UV/PMS in eliminating antibiotics is lacking up to now. Therefore, this review is intended to present the properties of UV sources, antibiotics, and PDS (PMS), to discuss the application of UV/PDS (PMS) in degrading antibiotics from the aspects of effect, influencing factors and mechanism, and to analyze and propose future research directions.

Comparative evaluation of MSW incineration leachate treatment by heterogeneous catalytic O3 and UV/O3: The unexpected contribution of high salinity and overlooked role of excited state

The efficiency and mechanism of heterogeneous catalytic O3 and UV/O3 for municipal solid waste (MSW) incineration leachate advanced treatment was systematically compared. Prior to comparison, catalyst used in heterogenous catalytic O3 and operation parameters for each technology were optimized. The COD removal of CuO@Al2O3/O3 under its optimal parameters was 57.2%, which failed to meet the standard (≥75%). In contrast, the COD removal by UV/O3 could be 82.3%. The superior efficiency of UV/O3 over CuO@Al2O3/O3 could be summarized into three aspects: (I) Cu bounded ·OH (≡Cu–O·) preferentially attacked hydrophilic groups, while free hydroxyl radical (·OH) was non-selective, thus UV/O3 exhibited a unique three-stage mechanism; (II) The oxidation potential of ≡Cu–O· was higher than that of ·OH, therefore was more vulnerable to the negative effect of radical self-quenching; (III) The existence of UV-induced excited states made organics in UV/O3 more active than in CuO@Al2O3/O3 system, thus high concentration of anions enhanced COD removal in UV/O3 but affected that in CuO@Al2O3/O3. The study further revealed the characteristics of heterogeneous catalytic O3 and UV/O3, and UV induced excited state should be considered in UV-based advanced oxidation processes (AOPs).

Reevaluation of radical-induced differentiation in UV-based advanced oxidation processes (UV/hydrogen peroxide, UV/peroxydisulfate, and UV/chlorine) for metronidazole removal: Kinetics, mechanism, toxicity variation, and DFT studies

Metronidazole (MNZ) is widely employed as an antibiotic, but it is recalcitrant in the water environment. The residual of MNZ has sparked significant concern because to its detrimental impacts on environmental safety and human health. In this study, the elimination of metronidazole (MNZ) was comparatively examined by UV/hydrogen peroxide (UV/H2O2), UV/peroxydisulfate (UV/PDS), and UV/chlorine processes. The best degradation rate constant was demonstrated by the UV/PDS (2.4 × 10−3 s−1), followed by UV/H2O2 AOP (1.0 × 10−3 s−1) and UV/chlorine AOP (3.7 × 10−4 s−1). The hydroxyl radicals (HO) played significant roles in UV-AOPs eliminating MNZ by 87.7 %, 30.2 %, and 43.0 % in UV/H2O2, UV/PDS, and UV/chlorine treatments, respectively. Additionally, the sulfate radical (SO4−) and chlorine radical (Cl) were essential for the elimination of MNZ, contributing 63.0 % and 36.2 %, respectively, in UV/PDS and UV/chlorine. The first-order rate constants (kobs) increase linearly with the increasing oxidant dosage in various UV-AOPs. The higher degradation efficiency of MNZ was observed in acid conditions due to the transition of oxygen active species. The presence of chloride (Cl−), bicarbonate (HCO3–), nitrate (NO3–), and humid acid (HA) remarkably inhabited the degradation of MNZ in UV/H2O2 and UV/PDS, whereas NO3– showed a promotion effect in UV/chlorine. In diverse water matrixes, UV/PDS usually consumed less electrical energy than UV/H2O2 and UV/chlorine. Combining density functional theory calculations and transformation products identification, it was revealed that HO was conducive to attack the nitrogenous heterocycle of MNZ via hydrogen atom transfer (HAT) and radical adduct formation (RAF) pathways, whereas SO4− and Cl oxidation favored RAF route. Some chlorine- and hydroxylation-intermediates, notably those produced in UV/chlorine AOP, displayed higher toxicity than the parent compounds. Overall, the findings unequivocally prove that UV-AOPs are effective, economical, and practical for the remediation of antibiotics-contaminated water.

Degradation and horizontal gene transfer analysis of plasmid-encoded antibiotic resistance genes during UV254, hydroxyl radical and sulphate radical treatments

The environment has been implicated with antibiotic resistance (AR). Effective degradation and deactivation of antibiotic resistance genes (ARGs) in wastewater treatment can serve as barriers to AR dissemination. This study investigated the degradation kinetics of intracellular (i-) and extracellular (e-) plasmid-encoded tetA, ampR and sul1 ARGs using UV254, hydroxyl radical (HO.) and sulphate radical (SO4.-) UV-based advanced oxidation processes (UV254/H2O2 and UV254/S2O82- respectively). The degradation of tetA, ampR and sul1 was quantified using quantitative polymerase chain reaction (qPCR). The damages to each ARG were observed using two qPCR amplicons ranging between 162 and 1054 bp. Culture-based horizontal gene transformation experiments were used to estimate the deactivation kinetics of pCR™2.1-TOPO AR plasmid. ARG degradation and deactivation kinetics were then compared to understand the roles of each treatment strategy in AR mitigation. Results indicate that extracellular ARGs degradation kinetics of the treatments followed an order UV254/S2O82- > UV254/H2O2 > UV254. The base pair specific kinetic constants with respect to HO. and SO4.- at pH 7 were between 1.86 × 109-1.65 × 1011 M−1s−1 and 2.87 × 109-5.84 × 1011 M−1s−1 respectively. e-ARGs degradation was at least 2-fold higher than i-ARGs degradation for all treatments. UV254/S2O82- was most effective for ARG degradation under acidic pH (5–6) while UV254/H2O2 was most effective between pH 7 and 8. Higher degradation rates were recorded for AT-rich ampR and longer qPCR amplicons. Deactivation rates by UV254/H2O2 and UV254/S2O82- were 2.6-times higher than that of UV254. Generally, deactivation kinetics were ∼ 8–13 times faster than degradation kinetics observed for short ampR amplicon. These findings show an overestimation of the potential risks of ARG presence using short qPCR target amplicons and the impact of nucleotide composition on ARG damage.

Inactivation of vancomycin-resistant Enterococcus faecalis and degradation of intracellular vanB gene under exposure to UV and UV/H2O2

The proliferation of antibiotic resistance in water environment which may cause antibiotic therapy failure has attracted worldwide attention. However, the effects of UV-based advanced oxidation processes on inactivation of antibiotic resistant bacteria (ARB) and degradation of antibiotic resistance genes (ARGs) have not been well studied. This study aimed to comparatively investigate the removal efficacy in inactivating the vancomycin-resistant Enterococcus faecalis (VRE) and degrading its containing vanB gene under exposure to UV and UV/H2O2. The results showed that VRE was readily inactivated in both UV and UV/H2O2 processes. Although UV/H2O2 was only slightly superior to UV alone in VRE inactivation, it significantly inhibited the bacterial photoactivation and regrowth. UV/H2O2 indeed achieved synergistic degradation of intracellular vanB (0.1–0.8 log), which could be further enhanced by increasing the UV intensity, lowering pH and adding H2O2 in batches. The enhanced induction of OH resulted in the cell membrane damage, facilitating the entrance of excess OH and more efficiently oxidizing the released intracellular ARGs. Overall, the presence of humic acid inhibited the inactivation of VRE and degradation of vanB, while lower concentrations of humic acid (2.5–5 mg/L) could act as free radical initiator and slightly promoted vanB degradation in UV/H2O2 process. Our findings suggested that UV/H2O2 has more advantages on the control of ARB and intracellular ARGs compared to UV alone.

Effective removal of furfural by ultraviolet activated persulfate, peroxide, and percarbonate oxidation: Focus on influencing factors, kinetics, and water matrix effect

In this study, the degradation of furfural by ultraviolet (UV) based advanced oxidation processes was investigated. The oxidation performance of percarbonate (PC), an alternative oxidant to hydrogen peroxide was evaluated with hydrogen peroxide (HP) and persulfate (PS) oxidation processes. UV was applied to activate oxidants and the effect of process variables (initial pH, oxidant dose, initial pollutant concentration) on furfural removal from aqueous solution was investigated. The optimum pH value was determined as 5 in the three processes. The optimum oxidant dose was determined as 5 mM in UV/HP and UV/PC processes, and 2.5 mM in the UV/PS process. Furfural removal efficiencies by UV/PS, UV/HP, and UV/PC processes were 94.7 %, 83.1 %, and 90.1 %, respectively at 25 mg/L initial furfural concentration. The pseudo-first-order reaction kinetic model was applied to determine the reaction kinetics in furfural degradation, and it was determined that UV-based advanced oxidation processes and furfural removal fit the first-order kinetic model with a high coefficient of determination values. The results showed that the removal efficiencies and reaction rate is directly proportional to the oxidant dose and inversely proportional to the initial furfural concentration. The effect of the water matrix on the furfural removal efficiency of the three processes was also investigated. The carbonate, bicarbonate, chloride, nitrate, and phosphate anions in the water decreased the removal efficiency at different rates, and this decrease was more pronounced in UV/HP and UV/PC processes. EE/O values calculated for UV/PS, UV/HP, and UV/PC processes were 20.90, 34.54, and 26.55 kWh/m3/order, respectively.

Degradation of geosmin and 2-methylisoborneol in UV-based AOPs for photoreactors with reflective inner surfaces: Kinetics and transformation products

Geosmin (GSM) and 2-methylisoborneol (2-MIB) are representative musty/earthy odor compounds commonly present in surface water. In present study, the degradation of GSM and 2-MIB subject to different UV-based advanced oxidation processes (AOPs), including UV/H2O2, UV/S2O82−, UV/chlorine, and UV/chloramine, in a phosphate-buffered saline (PBS) was conducted in a photoreactor with reflective inner surfaces and compared with that in an environmental water sample. A dynamic model to predict the degradation of GSM and 2-MIB in the photoreactor with reflective inner surfaces in the four UV-based AOPs was developed applying the second-order rate constants for the GSM and 2-MIB with primary reactive species (i.e., •OH, •Cl, and •SO4−) determined in this study. The model was proven to successfully simulate the degradation of GSM and 2-MIB. In addition, 8, 7, 8, and 11 degradation intermediates were detected from UV/H2O2, UV/S2O82−, UV/chlorine, and UV/chloramine in this study, and possible degradation pathways were proposed. This study is the first to report the degradation kinetics and formation products of GSM and 2-MIB in UV/chloramine. Research based on photoreactors with reflective inner surfaces may provide some guidance for eliminating GSM and 2-MIB in UV-based AOPs for full-scale engineering applications.

Elimination efficiency of synthetic musks during the treatment of drinking water with ozonation and UV-based advanced oxidation processes

This study investigated the reaction kinetics and elimination efficiency of eleven synthetic musks during ozonation and UV254nm-based, advanced oxidation processes. The synthetic musks containing olefin moieties with electron-donating alkyl substituents such as octahydro tetramethyl naphthalenyl ethanone (OTNE) and ambrettolide (AMBT) showed high reactivity toward ozone (k ≥ 3.7 × 105 M−1 s−1) and free available chlorine (FAC) (k = 9.2 – 88 M−1 s−1), while all other synthetic musks were less ozone reactive (k = 0.3 – 560 M−1 s−1) and FAC-refractory. All synthetic musks showed high •OH reactivity (k > 5 × 109 M−1 s−1), except musk ketone (MK) (k = 2.3 × 109 M−1 s−1). In concordance with the kinetic information, OTNE and AMBT were efficiently eliminated (>97%) in simulated ozone treatments of drinking water at a specific ozone dose of 0.5 gO3/gDOC. The elimination levels of the other synthetic musks were below 50% at 0.5 gO3/gDOC. The fluence-based UV photolysis rate constant of the synthetic musks was determined to be (0.2 – 2.7) × 10−3 cm2/mJ. The elimination levels of synthetic musks during UV alone treatment ranged from 7 to 81% at a UV fluence of 500 mJ/cm2. The addition of 10 mg/L H2O2 (UV/H2O2) significantly enhanced the elimination of most synthetic musks (achieving >90% elimination at 500 mJ/cm2), indicating that the •OH reaction was mainly responsible for their elimination. The addition of 10 mg/L FAC (UV/FAC) also significantly enhanced the elimination of olefinic and aromatic synthetic musks (>90%), for which the reaction with ClO• was mainly responsible. For MK and two alkyl synthetic musks, their elimination during UV/FAC treatment was still limited (28 – 64%) and was mainly achieved by UV photolysis or reaction with •OH. In summary, this study substantiates the chemical kinetics approach as a helpful tool for predicting or interpreting the elimination of micropollutants during oxidative water treatment.