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The degradation of atrazine (ATZ), sulfamethoxazole (SMX) and metoprolol (MET) in flow-through VUV/UV/H2O2 reactors was investigated with a focus on the effects of H2O2 dosage and reactor internal diameter (ID). Results showed that the micropollutants were degraded efficiently in the flow-through VUV/UV/H2O2 reactors following the pseudo first-order kinetics (R2 > 0.92). However, the steady-state assumption (SSA) kinetic model being vital in batch reactors was found invalid in flow-through reactors where fluid mixing was less sufficient. With the increase of H2O2 dosage, the ATZ removal efficiency remained almost constant while the SMX and MET removal was enhanced to different extents, which could be explained by the different reactivities of the pollutants towards HO•. A larger reactor ID resulted in lower degradation rate constants for all the three pollutants on account of the lower average fluence rate, but the change in energy efficiency was much more complicated. In reality, the electrical energy per order (EEO) of the investigated VUV/UV/H2O2 treatments ranged between 0.14–0.20, 0.07–0.14 and 0.09–0.26 kWh/m3/order for ATZ, SMX and MET, respectively, with the lowest EEO for each pollutant obtained under varied H2O2 dosages and reactor IDs. This study has demonstrated the efficiency of VUV/UV/H2O2 process for micropollutant removal and the inadequacy of the SSA model in flow-through reactors, and elaborated the influential mechanisms of H2O2 dosage and reactor ID on the reactor performances.

To ensure the safety of drinking water, ozone (O3) has been extensively applied in drinking water treatment plants to further remove natural organic matter (NOM). However, the surface water and groundwater near the coastal areas often contain high concentrations of bromide ion (Br−). Considering the risk of bromate (BrO3−) formation in ozonation of the sand-filtered water, the inhibitory efficiencies of hydrogen peroxide (H2O2) and ammonia (NH3) on BrO3− formation during ozonation process were compared. The addition of H2O2 effectively inhibited BrO3− formation at an initial Br− concentration amended to 350 µg/L. The inhibition efficiencies reached 59.6 and 100% when the mass ratio of H2O2/O3 was 0.25 and > 0.5, respectively. The UV254 and total organic carbon (TOC) also decreased after adding H2O2, while the formation potential of trihalomethanes (THMsFP) increased especially in subsequent chlorination process at a low dose of H2O2. To control the formation of both BrO3− and THMs, a relatively large dose of O3 and a high ratio of H2O2/O3were generally needed. NH3 addition inhibited BrO3− formation when the background ammonia nitrogen (NH3 N) concentration was low. There was no significant correlation between BrO3− inhibition efficiency and NH3 dose, and a small amount of NH3 N (0.2 mg/L) could obviously inhibit BrO3− formation. The oxidation of NOM seemed unaffected by NH3 addition, and the structure of NOM reflected by synchronous fluorescence (SF) scanning remained almost unchanged before and after adding NH3. Considering the formation of BrO3− and THMs, the optimal dose of NH3 was suggested to be 0.5 mg/L.

Permanganate (Mn(VII)) is a widely used oxidant in water treatment, which can oxidize trace organic contaminants (TrOCs) and Mn(II). Interestingly, this study found that presence of Mn(II) could accelerate the abatement of bisphenol A by Mn(VII) only under oxic condition. Herein, the effects of Mn(II) and dissolved oxygen (DO) on the abatement of TrOCs by Mn(VII) oxidation and the related mechanism were investigated. Results indicate that DO was involved in the Mn(VII)/Mn(II) reaction, with the reaction stoichiometry of Δ[Mn(VII)]:Δ[Mn(II)] determined to be 1:2 and 1:1.5 in the presence and absence of DO, respectively. Quenching and electron paramagnetic resonance tests verified that both superoxide radicals (O

Permanganate (PM) is a widely-used oxidant in water treatment. However, the oxidation rate of micro-pollutants by PM is highly variable, dependent on the electron density of certain moieties of micro-pollutants. Using a pesticide (carbendazim, CBZ) as a target micro-pollutant, this study compared the organic and inorganic activations of PM by benzoquinone (PM/BQ) and bisulfite (PM/BS), respectively. It was found that both the PM/BQ and PM/BS systems could accelerate the degradation of CBZ with different degradation rates. The PM/BS system completed the degradation of CBZ (96.6%) within 15 s, while the PM/BQ system took 2 h to achieve a 95.7% removal. The optimal molar ratios of [PM]ο:[BS]ο and [PM]ο:[BQ]ο were determined to be 1:5 and 1:0.1, respectively. Interestingly, both the degradation of CBZ in the PM/BQ and PM/BS systems were dependent on dissolved oxygen (DO) concentration. When DO was around 0.5 mg L−1, the removals of CBZ by the PM/BQ and PM/BS systems were just 3.6% and 36.8%, respectively after 2 h, significantly lower than those under 9.1-mg L−1 DO (95.7% and 96.6%, respectively). Based on the quenching experiments, the enhanced degradation in the PM/BQ system was mainly ascribed to the formations of Mn(III) and 1O2, while the formations of SO5 − and SO4 − mainly contributed to the accelerated degradation in the PM/BS system. The transformation products of CBZ in both the PM/BQ and PM/BS systems were identified and the degradation pathways including dehydrogenation, alkylation, carboxylation and hydroxylation were proposed. The inorganic activation of PM by BS exhibits a higher degradation rate and stability under different water matrices, indicating its potential engineering application in water treatment.

The decontamination of prometon (PMT) by ozone/hydroxylamine hydrochloride (O3/HAC) was systematically investigated in this study with focus on the degradation mechanism and kinetics. Experimental results revealed that there was an enhancement of PMT degradation efficiency by 42.1% and the pseudo-first-order rate constant by more than 5.7 times in O3/HAC process under low HAC dosage (5 mg L−1) after 3 min in comparison with O3 alone. The second-order rate constant of PMT with hydroxyl radical (•OH) was determined to be (1.84 ± 0.1) × 109 M−1 s−1 and 7.80 × 109 M−1 s−1 via competition kinetics and •OH steady-state hypothesis, respectively. The PMT removal in O3/HAC process was highly pH-dependent and the optimum degradation performance was achieved under pH 5.0. In addition, •OH and singlet oxygen were identified as the primary reactive oxygen radicals in O3/HAC process. Meanwhile, eleven transformation products of PMT were identified and possible degradation mechanisms were proposed. Moreover, a kinetic model based on chemical kinetics and steady-state hypothesis was developed and modified to predict the PMT abatement in O3/HAC process. The results demonstrated that the O3/HAC process provided a promising alternative for refractory organic pollutants decontamination in water treatment.

Permanganate is a versatile chemical oxidant, and has undergone a dramatic evolution toward deep insight into its reaction mechanism. However, the hydrogen abstraction of the N H bond by permanganate remains unclear. We studied the permanganate oxidation of the emerging micropollutant sulfamethoxazole in acidic aqueous solution. The reaction followed autocatalytic kinetics and demonstrated first-order with respect to each reactant. The presence of HMnO4 accelerated the reaction rate, which was four orders of magnitude higher than that of MnO4−. Based on the identified products, the rate-limiting step was determined to be simple N H bond oxidation by metal-oxo species permanganate. The mechanism was then studied computationally by density functional theory (DFT) using ammonia as the simplest model. Results showed that the N H bond oxidation by MnO4− (32.86 kcal/mol) was a concerted mechanism similar to that of C H bond oxidation, whereas HMnO4 oxidation of the N H bond (10.44 kcal/mol) was a stepwise electron-proton transfer. This reminds us that coordination of Bronsted acid could not only produce the stronger electrophile but also change the reaction mode by avoiding the bond cleavage in electron transfer process.

To date, little is known about the removal of fluoroquinolones (FQs) in the in-situ sludge ozone-reduction (SOR) process. Hence, this study investigated the behavior of five commonly used FQs, including ciprofloxacin, enrofloxacin, lomefloxacin, norfloxacin and ofloxacin in the SOR process. Batch experiments indicated that ozonation could effectively eliminate the target FQs present in the sludge, which was accelerated by increasing the initial pH (5.0–9.5). Continuous operation of an anaerobic/anoxic/oxic process coupled with sludge ozonation and phosphorus recovery showed that the SOR process could achieve zero yield of excess sludge. In addition, chemical oxygen demand and nitrogen species were stably removed, with efficiencies comparable to those obtained in the conventional activated sludge (CAS) process. However, an increase in the effluent total phosphorus concentration was observed in the SOR process. The effluent FQ concentrations in the SOR process remained quite stable and were close to those in the CAS process, whereas the FQ concentrations in the sludge decreased remarkably after ozonation. Mass balance analysis revealed that the FQs were released to the environment mainly through excess sludge disposal (69.9 ± 2.3%) in the CAS process, whereas were degraded mainly by ozone in the SOR process (75.8 ± 2.0%). Therefore, the SOR process was able to minimize the excess sludge and the release of FQs to the environment simultaneously.

Kinetic comparisons of micropollutant degradation by ultraviolet (UV) based advanced oxidation processes among various radiation sources are an important issue, yet this is still a challenge at present. This study investigated comparatively the kinetics of sulfamethazine (SMN) degradation by the UV/H2O2 process among three representative radiation sources, including low-pressure mercury UV (LPUV, monochromatic), medium-pressure mercury UV (MPUV, polychromatic), and vacuum UV(VUV)/UV (dual wavelengths causing different reaction mechanisms) lamps. Experiments were conducted with a newly developed mini-fluidic MPUV photoreaction system and a previously developed mini-fluidic VUV/UV photoreaction system. Measured and modeled results both indicate that the photon fluence-based SMN degradation rate constant ( kp') followed a descending order of VUV/UV/H2O2 > MPUV/H2O2 (200-300 nm) > LPUV/H2O2, and the kp' of the MPUV lamp was dependent on the wavelength range selected for photon fluence calculation. Analysis of potential errors revealed that a shorter effective path-length could have a lower error, and the maximum errors for the MPUV/H2O2 and LPUV/H2O2 processes in this study were 7.7% and 18.2%, respectively. This study has developed a new method for kinetic comparisons of micropollutant degradation by UV-AOPs among various radiation sources at bench-scale, which provides useful reference to practical applications.

With increasing water reuse as a sustainable water management strategy, antibiotic resistance genes (ARGs) which have been identified as emerging contaminants in wastewater are attracting global attentions. Given that wastewater treatment plants are now well-established as a sink and source of ARGs in both cell-associated and non-cell-associated forms, a need is acknowledged to reduce their proliferation and protect public health. Due to their different characteristics, cell-associated and non-cell-associated ARGs may have distinct responses to membrane filtration processes which are widely used as advanced treatment to the secondary effluent. This review improves the understanding of the abundance of cell-associated and non-cell-associated ARGs in wastewaters and the secondary effluents and compares the elimination of ARGs in cell-associated and non-cell-associated forms by low-pressure and high-pressure membrane filtration processes. The former process reduces the concentration of cell-associated ARGs by more than 2-logs on average. An increase of the retention efficiency of non-cell-associated ARGs is observed with decreasing molecular weight cut-offs in ultrafiltration. The high-pressure membrane filtration (i.e., nanofiltration and reverse osmosis) can effectively eliminate both cell-associated and non-cell-associated ARGs, with averagely more than 4.6-log reduction. In general, the two forms of ARGs can be removed from water by the membrane filtration processes via the effects of size exclusion, adsorption, and electrostatic repulsion. The size and conformation of cell-associated and non-cell-associated ARGs, characteristics of membranes, coexisting substances, and biofilm formation influence ARG retention. Accumulation and potential proliferation of cell-associated and non-cell-associated ARGs in foulants and concentrate and corresponding control strategies warrant future research.

Morphology, the important feature of bloom-forming cyanobacteria, was studied for its impacts on the harmful cyanobacterial bloom (HCB) treatment by coagulative colloidal ozone microbubbles (CCOMBs). The globally-appeared HCB species - Microcystis aeruginosa (spherical cells, block mass colonies), Microcystis panniformis (spherical cells, flat penniform-like colonies) and Anabaena flos-aquae (filamentous morphology) were chosen as representative species. CCOMBs were generated by modifying the bubble surface and the gas core with coagulant and ozone, respectively. The removal of spherical cells and filaments was 99.5% and ≤ 34.6%, individually, and the latter was ascribed to chain breakage. CCOMBs collected Microcystis panniformis via complexing with the fluorescent and non-fluorescent functional groups of cell colonies but captured Anabaena flos-aquae through the fluorescent ones. More Microcystis aeruginosa got membrane-damaged than Microcystis panniformis; nevertheless, the microcystin-LR (MC-LR) removal was guaranteed through efficiently oxidizing the released MC-LR. Although the outer peptidoglycan sheet of Anabaena flos-aquae was destroyed, the inner cyte membrane remained intact, preventing intracellular MC-LR from releasing. The HCBs dominated by single species with spherical cells were more readily treated than those with co-occurred species. The toxicological tests imply that, as a robust tool for HCB treatment, the CCOMB technology could be eco-environmentally friendly to the aquatic environment.

Significant iron release from cast iron pipes in water distribution systems (WDSs), which usually occurs during the source water switch period, is a great concern of water utilities because of the potential occurrence of “red water” and customer complaints. This study developed a new method which combined in-situ water stagnation experiments with mathematical models and numerical simulations to predict the iron release caused by source water switch. In-situ water stagnation experiments were conducted to determine the total iron accumulation in nine cast iron pipes in-service in Beijing when switching the local water to treated Danjiangkou Reservior water. Results showed that the difference in the concentration increment of total iron in 24 hr (ΔCITI,24), i.e. short-term iron release, caused by source water switch was mainly dependent on the difference in the key quality parameters (pH, hardness, nitrate, Larson Ratio and dissolved oxygen (DO)) between the two source waters. The iron release rate (RFe) after switch, i.e. long-term iron release, was closely related to the pipe properties as well as the DO and total residual chlorine (TRC) concentrations. Mathematical models of ΔCITI,24 and RFe were developed to quantitatively reveal the relationship between iron release and the key quality parameters. The RFe model could successfully combine with EPANET-MSX, a numerical simulator of water quality for WDSs to extend the iron release modeling from pipe level to network level. The new method is applicable to predicting iron release during source water switch, thus facilitating water utilities to take preventive actions to avoid “red water”.

Cupric oxide (CuO) is able to catalyze the reactions among disinfectant, extracellular polymeric substances (EPS) and bromide (Br

In recent years, ultraviolet (UV) based advanced oxidation processes have been extensively studied for degradation of refractory organic pollutants in water and wastewater, and selection of an appropriate UV light source is an important issue. In this study, bench-scale tests were conducted on a mini-fluidic photoreaction system (MFPS) to determine the degradation kinetics of methylene blue (MB) by UV/peroxydisulfate (UV/PDS) process equipped with a low-pressure UV (LPUV), vacuum UV (VUV)/LPUV, or medium-pressure UV (MPUV) mercury vapor lamp. Results indicate that MB degradation by UV/PDS with various light sources all followed the pseudo-first order kinetics, and the photon fluence-based rate constant (k

The spread of antibiotic resistance in the aquatic environment severely threatens the public health and ecological security. This study investigated simultaneously capturing and inactivating/oxidizing the antibiotic resistant bacteria (ARB) and cell-free antibiotic resistance genes (ARGs) in waters by flexibly-functionalized microbubbles. The microbubbles were obtained by surface-modifying the bubbles with coagulant (named as coagulative colloidal gas aphrons, CCGAs) and further encapsulating ozone in the gas core (named as coagulative colloidal ozone aphrons, CCOAs). CCGAs removed 92.4-97.5% of the sulfamethoxazole-resistant bacteria in the presence of dissolved organic matter (DOM), and the log reduction of cell-free ARGs (particularly, those encoded in plasmid) reached 1.86-3.30. The ozone release from CCOAs led to efficient in-situ oxidation: 91.2% of ARB were membrane-damaged and inactivated. In the municipal wastewater matrix, the removal of ARB increased whilst that of cell-free ARGs decreased by CCGAs with the DOM content increasing. The ozone encapsulation into CCGAs reinforced the bubble performance. The predominant capture mechanism should be electrostatic attraction between bubbles and ARB (or cell-free ARGs), and DOM enhanced the sweeping and bridging effect. The functionalized microbubble technology can be a promising and effective barrier for ARB and cell-free ARGs with shortened retention time, lessened chemical doses and simplified treatment unit.

Quinone group is an important fraction of humic acid. The pseudo-first-order rate constant (kobs) of levofloxacin (LF) degradation by permanganate (MnO4−) significantly increased from 0.010 (without benzoquinone, BQ) to 0.042–0.443 min−1 at [BQ]o:[MnO4−]o (molar ratio) = 0.03–0.25 at pH 7.5, and an acidic pH facilitated LF degradation. In the presence of BQ, MnO4− was first reduced to Mn(II). Then, Mn(II) reacted with BQ to produce Mn(III) and semiquinone radical, which was promoted under acidic conditions. With dissolved oxygen available, Mn(III) further oxidized semiquinone radical to produce singlet oxygen (1O2) and superoxide radical (O2 −) as well as regenerate BQ. In addition, MnO4− could also react with Mn(II) to produce Mn(III), whose complexation with semiquinone radical in turn promoted this reaction. Due to the predominant scavenging of O2 − by BQ, 1O2 and Mn(III) mainly contributed to the accelerated LF degradation, with a notable formation of hydroxyl, ketone and endoperoxide groups in the degradation byproducts. This study helps better understand the role of natural organic matter in the degradation of organic micropollutants by MnO4− in water treatment.

Ozonation is a promising means for the reduction of excess sludge in wastewater treatment plants. However, little information is available on the removal of antibiotics during sludge ozonation. Therefore, this study investigated first the behavior of four commonly-used hydrophobic antibiotics, including three tetracyclines (tetracycline, oxytetracycline, and doxycycline) and one macrolide (azithromycin) in activated sludge process and then their removal during sludge reduction by ozone. Results indicate that the studied antibiotics were primarily transferred into the solid phase of activated sludge via sorption, which was a reversible, spontaneous, and exothermic process governed by surface reactions. Sludge ozonation could effectively remove 86.4–93.6% of the antibiotics present in the sludge at an ozone dose of 102 mg per gram of mixed liquor suspended solids and pH 7.2. The removal of studied antibiotics mainly proceeded through desorption and subsequent oxidation. Increasing the initial pH from 5.0 to 9.5 obviously enhanced the antibiotic removal during sludge ozonation. This study demonstrated that the activated sludge process coupled with sludge ozonation can simultaneously reduce excess sludge and eliminate antibiotics.

The employment of ultraviolet (UV) disinfection in secondary water supply (SWS) systems has been a prevalent practice in recent years in China. However, highly fluctuating flow rates make the regular running of such UV disinfection reactors (i.e., lighting all the lamps all the time) a considerable waste of energy. In this study, an economical-running strategy, which consisted of various lamp operation modes for different time periods, was developed for a 6-lamp UV disinfection reactor in a SWS system. Reactor performances with lamp modes of different lamp output powers (LOPs) were simulated with computational fluid dynamics. Results show that the flow rate in the SWS system varied significantly in a day but shared similar daily variation patterns in the long term. This provided the basis for the economical running of the reactor by reducing the LOP periodically. The optimal lamp mode for a constant LOP was determined by comparing the corresponding reduction equivalent fluences (REFs), which was always found with the on–off switching solution (i.e., switching on/off the lamps according to the flow rates). The mixing efficiency factors (MEFs) of the reactor with various lamp modes were also discussed. The developed economical-running strategy for the reactor could save 32% of energy. This study established a methodology for the economical-running strategy development for UV disinfection reactors in SWS systems and provided an insight into the reactor performance at reduced LOPs.

Removal of sulfonamides (SAs) by an integrated ozonation and biological activated carbon filtration (O3-BAC) process, as an advanced drinking water treatment process, was evaluated in a pilot-scale study. Furthermore, the effects of the O3-BAC process on sulfonamide-resistant bacteria (SRB) and on the removal of total organic carbon, UV254, and turbidity were investigated. Results indicate that ozonation could effectively remove SAs from water at an appropriate ozone dose with an improvement of water quality; however, BAC filtration would lead to an increase of SRB. In addition, the performance of the integrated process in eliminating disinfection byproducts formation potential (DBPsFP) in chlorination was evaluated. The results show ozonation would result in an increase of DBPsFP, while subsequent BAC filtration could effectively reduce DBPsFP to the safety-standard level of water quality. Overall, effective removal was achieved by the O3-BAC process in terms of the reduction of SAs but not of SRB. Subsequent disinfection is significant and biological safety should be evaluated further to ensure the effectiveness of the integrated process and the security of water quality.

As an advanced oxidation process, vacuum ultraviolet/ultraviolet (VUV/UV) process has recently gained increasing attention in water treatment, but assessment of its technical and economic feasibility for pesticide removal has rarely been conducted. This study investigated the degradation of five typical pesticides, including aldicarb (ALD), alachlor (ALA), chloroneb (CHL), methiocarb (MET) and atrazine (ATR), by VUV/UV under simulated water treatment conditions at both bench- and pilot-scales. Bench-scale tests showed that pesticide degradation followed pseudo-first-order kinetics and all pesticides were degraded by >90% at a VUV fluence of 12 mJ cm−2. The second-order reaction rate constants of ALD, ALA, CHL, MET and ATR with HO were 7.57 × 109, 4.89 × 109, 2.57 × 109, 3.81 × 109 and 2.38 × 109 M−1 s−1, respectively. Solution pH had varying influences on the degradation of different pesticides by VUV/UV. Inorganic anions (Cl−, NO3−, HCO3−) and natural organic matter (NOM) inhibited pesticide degradation by scavenging HO , but SO42− slightly promoted pesticide degradation. The toxicity of pesticide solutions was reduced by 33.7% to 74.8% after the VUV/UV treatment. In a long-term (80 d) operation of the pilot reaction system using a sand-filtered water, the stable performance with acceptable energy consumption (0.27–1.52 kWh m−3 Order−1) suggested a good application potential of the VUV/UV process for pesticide removal in small-scale water treatment.

The vacuum-ultraviolet/ultraviolet/chlorine (VUV/UV/chlorine) process, with a VUV/UV mercury lamp used as the light source, was found to be a highly efficient advanced oxidation process (AOP) in a previous study. Hence, its application feasibility for trace organic pollutant removal from drinking water becomes attractive. In this work, a bench-scale mini-fluidic VUV/UV photoreaction system was used to determine the degradation kinetics of sulfamethazine (SMN), a model sulfonamide antibiotic frequently detected with trace levels in aquatic environments. Results indicated that SMN (0.1 mg L–1) could be degraded rapidly by VUV/UV/chlorine, and a synergism was observed between the VUV/UV and UV/chlorine processes. Photon-fluence based rate constants of SMN degradation were determined to be 6.76 × 103 and 8.51 × 103 m2 einstein–1 at chlorine doses of 0.05 and 0.5 mg L–1, respectively. The presence of natural organic matter in real waters significantly inhibited SMN degradation. In addition, pilot tests were co...

Effects of bromide (Br − ) and iodide (I − ) on chlorination kinetics of diclofenac (DCF) and potential disinfection by-products (DBPs) formation were investigated in this study. The presence of either Br − or I − accelerated the chlorination of DCF with different extents. Then species-specific apparent second-order rate constants ( k app ) of DCF with free chlorine (FC), free bromine (FB), free iodine (FI) were determined. It was found that the reactivity rate of FB with DCF was higher than those of FC and FI. The k app,FB-DCF at pH 7.0 was determined to be 9320 M −1 s −1 , which was 3680 and 3.2 folds of those of FC and FI, respectively. The k app,FC-DCF were highly pH-dependent, while the k app values of DCF with FB and FI were less influenced by pH than FC. The presence of Br − and I − enhanced the formation amounts and altered the speciation of DBPs. The DBPs formation amounts were enhanced from 67.2 to 292.0 μg L −1 and 87.3 μg L −1 , respectively, when 50 μM Br − or I − was spiked. Meanwhile, the dominant species of formed DBPs shifted from chlorinated DBPs to brominated and iodinated DBPs. At last, the transformation by-products and pathways of DCF under chlorination, chlorination with Br − and chlorination with I − were proposed and compared. The DCF transformation pathways mainly proceeded through hydroxylation, decarboxylation and substitution reactions. Although the presence of Br − and I − accelerated the chlorination of DCF, the enhanced formation of brominated and iodinated DBPs highlights the necessity to remove Br − and I − from source water prior to chlorination for mitigating the formation of toxic DBPs.

The degradation of sulfamethazine (SMN) by VUV/UV photo-Fenton (VPF) process was investigated with a mini-fluidic VUV/UV photoreaction system. Compared with the conventional UV photo-Fenton process, the VPF process significantly enhanced the degradation and mineralization of SMN, because the VUV irradiation photolyzed H2O and accelerated the redox cycle of Fe3+/Fe2+ to generate more reactive oxygen species (ROS). Initial pH and concentrations of SMN, H2O2, Fe3+, inorganic anions (NO3−, HCO3−, and Cl−), and humic acid all considerably impacted SMN degradation in the VPF process. In particular, the initial SMN concentration significantly affected the absorption distributions of UV and VUV photons in the reaction solution, thus inducing a different reaction mechanism. At a lower SMN concentration (1.8 μM), most of UV and VUV photons were absorbed by Fe3+ and H2O, respectively, so indirect oxidation by ROS mainly accounted for SMN degradation. However, at a higher SMN concentration (90 μM), 89.2% of UV photons and 59.0% of VUV photons were absorbed by SMN, so direct photolysis also played an important role. In addition, HO and HO2 were identified as the main ROS in the VPF process. This study demonstrates that the VPF process can effectively remove organic micropollutants from water.

Pipe failure often occurs in water distribution networks (WDNs) and results in high levels of water loss and socio-economic damage. Physical-based, statistical and data-driven models have been developed to estimate pipe failure rates (failures per km of pipe per year) to efficiently manage water losses from WDNs and to ensure safe operations. Due to the complexities of pipe failure patterns, we develop a superposed statistical model to depict the relationship between pipe failure rate and pipe age. The model’s level of uncertainty was then quantified by simulating pipe failures as Poisson numbers. Part of Beijing’s WDN is taken as a study case, and pipe failure data for a 4-year period, as well as pipe properties, are collected to develop the pipe failure model. The case study results show that the pipe failure rates vary with time in a non-monotonic manner and that the proposed model captures pipe failure behaviour with an R2 value of 0.95. A 95% confidence interval of modelled pipe failures for each pipe age group is used to describe the uncertainty level of the model. We find that 88% of the observations fall under the 95% confidence interval. The established model could be applied to prioritize pipes with higher failure rates to optimize pipe replacement/rehabilitation strategies. Our uncertainty analysis of this model can help utility managers understand the model’s reliability and formulate reasonable WDN management plans.

Quinclorac, a widely used herbicide in agriculture, has been recognized as an emerging environmental pollutant owing to its long persistence and potential risk to humans. However, no related information is available on the degradation of quinclorac by employing oxidants. Herein, the reactivity of quinclorac with permanganate was systematically investigated in water by combining experimental and computational approaches. The reaction followed overall second-order kinetics pointing to a bimolecular rate-limiting step. The second-order rate constant was found to be 3.47 × 10-3 M-1 s-1 at 25 °C, which was independent of pH over the range from 5 to 9 and was dependent on temperature over the range from 19 to 35 °C. The initial product was identified by UPLC-Q-TOF-MS to be mono-hydroxylated quinclorac, which was more susceptible to further oxidation. The result could be supported by the complete simulation of the reaction process in DFT calculations, indicating the [3 + 2] cycloaddition oxidation of the benzene ring in the rate-limiting step. The plausible mechanism was then proposed, accompanied by the analysis of the HOMO indicating the hydroxylation position and of the ESP suggesting a more electron-rich moiety. Considering the high effectiveness and low toxicity, permanganate oxidation was considered to be a very promising technique for removing quinclorac from aquatic environments.

As an emerging environmental contaminant, the herbicide quinclorac has attracted much attention in recent years. However, a very fundamental issue, the acid dissociation of quinclorac has not yet to be studied in detail. Herein, the pKa value and the corresponding structures of quinclorac were systematically investigated using combined experimental and theoretical approaches. The experimental pKa of quinclorac was determined by the spectrophotometric method to be 2.65 at 25 °C with ionic strength of 0.05 M, and was corrected to be 2.56 at ionic strength of zero. The molecular structures of quinclorac were then located by employing the DFT calculation. The anionic quinclorac was directly located with the carboxylic group perpendicular to the aromatic ring, while neutral quinclorac was found to be the equivalent twin structures. The result was further confirmed by analyzing the UV/Vis and MS-MS2 spectra from both experimental and theoretical viewpoints. By employing the QSPR approach, the theoretical pKa of QCR was determined to be 2.50, which is excellent agreement with the experimental result obtained herein. The protonation of QCR at the carboxylic group instead of the quinoline structure was attributed to the weak electronegative property of nitrogen atom induced by the electron-withdrawing groups. It is anticipated that this work could not only help in gaining a deep insight into the acid dissociation of quinclorac but also offering the key information on its reaction and interaction with others.

Turbidity is a common parameter used to assess particle concentration in water using visible light. However, the fact that particles play multiple roles (e.g., scattering, refraction, and reflection) in influencing the optical properties of aqueous suspensions complicates examinations of their effects on ultraviolet (UV) photoreactor performance. To address this issue, UV fluence rate (FR) distributions in a photoreactor containing various particle suspensions (SiO2, MgO, and TiO2) were measured using a microfluorescent silica detector (MFSD). Reflectance of solid particles, as well as transmittance and scattering properties of the suspensions were characterized at UV, visible, and infrared (IR) wavelengths. The results of these measurements indicated that the optical properties of all three particle types were similar at visible and IR wavelengths, but obvious differences were evident in the UV range. The FR results indicated that for turbidity associated with SiO2 and MgO suspensions, the weighted avera...

Sulfonamides (SAs), commonly used as human and veterinary antibiotics, are of great concerns because of their frequent detections in aquatic environment. This study investigated the oxidation of six SAs (i.e., sulfamethoxazole (SMX), sulfamethizole, sulfamethazine, sulfadimethoxine, sulfamerazine, and sulfathiazole) by chlorine dioxide (ClO2). The results indicate that the reactions followed the second-order kinetic model, with rate constants ranging from 3.85 × 103 to 2.59 × 104 M−1 s−1 at pH 7.0 and 20 °C. For each SA, the rate constant increased by 1.6–2.2 orders of magnitude as the solution pH increased from 4.0 to 9.5. The activation energies of the selected SAs ranged from 31.6 to 39.8 kJ mol−1. In addition, SMX was selected as a model compound to explore the degradation pathways during ClO2 oxidation. The reactivity of SMX toward ClO2 was strongly related to the ionization equilibrium of the amido-nitrogen in SMX molecule. The cleavage of S N and C S bonds and the hydroxylation of aniline moiety in the SMX molecule constituted the major degradation pathways. ClO2 oxidation was likely to decrease the antibacterial activity of SMX solution because of the destruction of p-aminobenzenesulfonamide moiety. The obtained rate constants could well predict the fate of SAs during ClO2 oxidation in a surface water, where an effective removal of SAs by ClO2 can be expected under practical water treatment conditions.

Natural estrogens (NEs) discharged from wastewater treatment plants (WWTPs) have drawn great attention because of their potential risks to aquatic ecosystems. However, neglect of the conjugated natural estrogens (C-NEs) has caused large discrepancies among different studies on the removal of NEs in WWTPs. The present work investigated the transformation and fate of three NEs and six corresponding C-NEs along wastewater treatment processes. The removal efficiencies of the target estrogens (i.e., NEs and C-NEs) and their correlations with the operational parameters were determined over a twelve-month monitoring period at a typical WWTP adopting a combined bio-treatment process (i.e., anaerobic/anoxic/oxic process followed by a moving-bed biofilm reactor). The concentration variations of the target estrogens along the treatment processes were examined to differentiate the transformation and fate of NEs and C-NEs. Moreover, lab-scale experiments were conducted to clarify the removal pathways of C-NEs in the bio-treatment process. Results indicate that both NEs and C-NEs could pass through the treatment processes, thus being frequently detected in the effluent and excess sludge. The aqueous removal efficiencies of NEs and C-NEs were significantly correlated with the sludge retention time and temperature, respectively. C-NEs were more persistent than NEs, so considerably high conjugated ratios (13.5-100.0%) were detected in the effluent. Sulfate conjugates presented a lower adsorption affinity to sludge and a slower hydrolysis rate than glucuronide conjugates, which makes the former more recalcitrant to biodegradation. This study highlights the challenge on the elimination of NEs, particularly their conjugates, by wastewater treatment processes.

Levofloxacin (LF) is a frequently detected fluoroquinolone in surface water, and permanganate (MnO4-) is a commonly used oxidant in drinking water treatment. This study investigated the impact of humic acid (HA) on LF degradation by aqueous MnO4- from both kinetic and mechanistic aspects. In the absence of HA, the second-order rate constant (k) of LF degradation by MnO4- was determined to be 3.9 M-1 s-1 at pH 7.5, which increased with decreasing pH. In the presence of HA, the pseudo-first-order rate constant (kobs) of LF degradation at pH 7.5 was significantly increased by 3.8- and 2.8-fold at [HA]o:[KMnO4]o (mass ratio) = 0.5 and 1, respectively. Secondary oxidant scavenging and electron paramagnetic resonance tests indicated that HA could form a complex with Mn(III), a strongly oxidative intermediate produced in the reaction of MnO4- with HA, to induce the successive formation of superoxide radicals (O2-) and hydroxyl radicals (OH). The resulting OH primarily contributed to the accelerated LF degradation, and the complex [HA-Mn(III)] could account for the rest of acceleration. The degradation of LF and its byproducts during MnO4- oxidation was mainly through hydroxylation, dehydrogenation and carboxylation, and the presence of HA led to a stronger destruction of LF. This study helps better understand the degradation of organic micropollutants by MnO4- in drinking water treatment.

This study investigated the degradation kinetics and halonitromethanes formation potential (HNMsFP) of two nitro-based pharmaceuticals (i.e., ranitidine (RNTD) and nizatidine (NZTD)) during ultraviolet (UV) photolysis. It was found that the degradation kinetics of RNTD and NZTD exhibited pH-dependent trends, in accordance with their deprotonation equilibria. The neutral species of RNTD and NZTD were more photo-reactive than their corresponding deprotonated species, with their specific fluence-based first-order rate constants varying in the range of 5.64–31.90 m 2 E −1 . Both the RNTD and NZTD were prone precursors of HNMs (with molar yields of 5.6± 0.3% and 4.7± 0.4%, respectively at pH 7.0). Acidic and neutral circumstances facilitated the HNMs formation. The UV photolysis of RNTD and NZTD could reduce their HNMsFP simultaneously. Positive linear relationships between residual RNTD or NZTD concentration and HNMsFP were observed and the denitration during the UV photolysis accounted for the HNMsFP reduction. With the mandatory UV disinfection fluences in China (i.e. 20–80 mJ cm −2 ), the effective abatement of RNTD and NZTD and their HNMsFP could not be fully achieved, highlighting the necessity of increasing UV fluence or developing UV-based advanced oxidation process in future.

Reaction of Fe(VI) with 2,2'-azino-bis-(3-ethylbenzothiazoline -6-sulfonate) (ABTS) is widely adopted to determine aqueous ferrate (Fe(VI)) concentration based on ABTS+ formation. Interestingly, this study found that the addition of ABTS could accelerate the oxidation of diclofenac (DCF) by Fe(VI) significantly. Observed first-order rate constant of DCF in the presence of 30μM ABTS was found to be 36.2 folds of that without ABTS, with values of 3.08 and 0.085min-1, respectively. It was partly attributed to the formation of ABTS+. The apparent second-order rate constant (kapp) for the oxidation of ABTS by Fe(VI) at pH7.0 was determined to be 1.1×106M-1s-1, which was 3-5 orders of magnitude higher than those for the reactions of ABTS+ with DCF (kapp,ABTS+-DCF=2.8×103M-1s-1) and Fe(VI) with DCF (kapp,Fe(VI)-DCF=17.7M-1s-1). Both the kapp,Fe(VI)-ABTS and kapp,Fe(VI)-DCF decreased obviously with increasing pH, while the kapp,ABTS+-DCF exhibited little pH dependency. By acting as the electron shuttle, ABTS could enhance the removal efficiency of DCF over wide pH and natural organic matter concentration ranges. This study provides new insights to reconsider the role of organic matter during Fe(VI) oxidation and highlights the potential for increasing the reactivity of Fe(VI).

The detailed sorption steps and biodegradation characteristics of fluoroquinolones (FQs) including ciprofloxacin, enrofloxacin, lomefloxacin, norfloxacin, and ofloxacin were investigated through batch experiments. The results indicate that FQs at a total concentration of 500μg/L caused little inhibition of sludge bioactivity. Sorption was the primary removal pathway of FQs in the activated sludge process, followed by biodegradation, while hydrolysis and volatilization were negligible. FQ sorption on activated sludge was a reversible process governed by surface reaction. Henry and Freundlich models could describe the FQ sorption isotherms well in the concentration range of 100-300μg/L. Thermodynamic parameters revealed that FQ sorption on activated sludge is spontaneous, exothermic, and enthalpy-driven. Hydrophobicity-independent mechanisms determined the FQ sorption affinity with activated sludge. The zwitterion of FQs had the strongest sorption affinity, followed by cation and anion, and aerobic condition facilitated FQ sorption. FQs were slowly biodegradable, with long half-lives (>100hr). FQ biodegradation was enhanced with increasing temperature and under aerobic condition, and thus was possibly achieved through co-metabolism during nitrification. This study provides an insight into the removal kinetics and mechanism of FQs in the activated sludge process, but also helps assess the environmental risks of FQs resulting from sludge disposal.

As an environment-friendly activator, iron ions (Fe(II) and Fe(III)) have been extensively studied in homogeneous activation of persulfate (PS) to remove organic pollutants from water. However, the slow reduction of Fe(III) to Fe(II) and the subsequent low activation efficiency limit the wide applications of PS/Fe(II) or PS/Fe(III). In this study, the roles of four complexing agents, including gallic acid (GA), ethylene diamine tetraacetic acid, ( S,S )-ethylenediamine- N,N ′-disuccinic acid trisodium salt and citric acid in the activation of PS/Fe(III) were comparatively investigated with iopamidol (IPM) used as a model organic pollutant. Results indicate that GA was the most effective with an increase in the observed pseudo-first-order rate constant ( k obs ) by 9.2 folds for IPM degradation by PS/Fe(III). Through radical scavenger (ethanol and tert -butanol) tests and electron paramagnetic resonance analysis, HO and SO 4 − were identified to be responsible for the accelerated degradation of IPM, and HO played a more important role. Intrinsically, the promoted Fe(III) reduction and PS decomposition accelerated the degradation of IPM. The transformation by-products of IPM in the PS/Fe(III)/GA system were identified and potential degradation pathways were proposed. Besides, the accelerated degradation of other three organic pollutants (methyl orange, congo red, and diclofenac) further demonstrated the applicability of the PS/Fe(III)/GA system to water treatment.

The reaction between tetracycline and alkaline permanganate was investigated by combining experimental and computational methods. The kinetics was initially studied using a stopped-flow technique and was found to be first-order in tetracycline and permanganate. The second-order rate constant was positive linearly dependent on the concentration of hydroxyl ion (0.01–0.10 M), indicating the presence of base catalysis. By construction of the Eyring plots in the range of 293–308 K, a lower activation barrier ((14.89 ± 0.44) kcal mol–1) was obtained at 298 K for the base-catalyzed pathway compared with that ((17.72 ± 1.84) kcal mol–1) for the uncatalyzed pathway. The effect of ionic strength further suggested the existence of a complex with higher charge and reactivity. It is confirmed by the theoretical analysis that the hydroxyl ion could attract the proton of tetracycline toward itself to form a complex-like structure with a highly reactive phenolate-type moiety. The highest occupied molecular orbital of te...

Peroxymonosulfate (PMS) is a promising alternative for drinking water disinfection; also many organic micropollutants may be present in drinking water sources nowadays. However, pipe corrosion products (PCPs) may impact the reactions between a disinfectant and organic micropollutants in water distribution systems. This study investigated iopamidol (IPM) degradation by PMS under catalysis of two PCPs (i.e., CuO and δ-MnO 2 ). The pseudo-first-order rate constant of IPM degradation in the CuO/PMS system (CuPS) was 3.7 times of that in the δ-MnO 2 /PMS system (MnPS), with values of 0.218 and 0.059 min −1 , respectively. Sulfate radical (SO 4 − ) was the major contributor to IPM degradation in the CuPS, while hydroxyl radical (HO ) also played an important role in the MnPS. The radical yield ratio was 0.89 and 0.69 mol/mol in the CuPS and MnPS, respectively. The IPM degradation rate increased with increasing PMS dose, and reached a maximum with a PCP dose of 1.0 and 1.5 g L −1 in the CuPS and MnPS, respectively. The highest degradation efficiency was achieved at pH 7.0 in the two systems. The water matrix (i.e., natural organic matter, alkalinity and chloride) had detrimental effects on IPM degradation to different degrees. The majority of the iodine released from IPM was oxidized to iodate (IO 3 − ) and a small fraction of the initial total organic iodine was transformed to iodoform (CHI 3 ). The IPM degradation by PMS mainly proceeded through two pathways: (1) amide hydrolysis of side chain A, amino oxidation, and amide hydrolysis of side chains B and B′ in sequence; and (2) deiodination reactions.

The performance of a medium-pressure (MP) mercury lamp photoreactor is strongly influenced by the spatial photon fluence rate (PFR) distributions which are wavelength-dependent. To address this issue, PFR distributions in an MP lamp photoreactor were measured using a 360-degree response microfluorescent silica detector (MFSD). To accurately express the optical behavior in an MP photoreactor, PFR, MFSD response PFR (PFRMFSD), and effective germicidal PFR (PFRGER) were defined and compared. The measured axial and radial PFRMFSD values agreed well with the corresponding results from a simulation model (UVCalc). The PFR and PFRGER were obtained from the measured PFRMFSD by using correction factors calculated by the UVCalc. Under identical UV transmittance (254 nm) conditions (75% and 85%), the weighted average PFRGER values were 13.3–18.7% lower than the corresponding PFR values, indicating that PFRGER, rather than PFR should be used in MP photoreactor design to meet disinfection standards. Based on measured ...

The occurrence of antibiotics in the environment has recently raised serious concern regarding their potential threat to aquatic ecosystem and human health. In this study, the magnetic ion exchange (MIEX) resin was applied for removing three commonly-used antibiotics, sulfamethoxazole (SMX), tetracycline (TCN) and amoxicillin (AMX) from water. The results of batch experiments show that the maximum adsorption capacities on the MIEX resin for SMX, TCN and AMX were 789.32, 443.18 and 155.15μg/mL at 25°C, respectively, which were 2-7 times that for the powdered activated carbon. The adsorption kinetics of antibiotics on the MIEX resin could be simulated by the pseudo-second-order model (R2=0.99), and the adsorption isotherm data were well described by the Langmuir model (R2=0.97). Solution pH exhibited a remarkable impact on the adsorption process and the absorbed concentrations of the tested antibiotics were obtained around the neutral pH. The MIEX resin could be easily regenerated by 2mol/L NaCl solution and maintained high adsorption removal for the tested antibiotics after regeneration. Anion exchange mechanism mainly controlled the adsorption of antibiotic and the formation of hydrogen binding between the antibiotic and resin can also result in the increase of adsorption capacity. The high adsorption capacity, fast adsorption rate and prominent reusability make the MIEX resin a potential adsorbent in the application for removing antibiotics from water.

ConspectusFormation of iodinated disinfection byproducts (I-DBPs) in drinking water has become an emerging concern. Compared to chlorine- and bromine-containing DBPs, I-DBPs are more toxic, have different precursors and formation mechanisms, and are unregulated. In this Account, we focus on recent research in the formation of known and unknown I-DBPs in drinking water. We present the state-of-the-art understanding of known I-DBPs for the six groups reported to date, including iodinated methanes, acids, acetamides, acetonitriles, acetaldehyde, and phenols. I-DBP concentrations in drinking water generally range from ng L–1 to low-μg L–1. The toxicological effects of I-DBPs are summarized and compared with those of chlorinated and brominated DBPs. I-DBPs are almost always more cytotoxic and genotoxic than their chlorinated and brominated analogues. Iodoacetic acid is the most genotoxic of all DBPs studied to date, and diiodoacetamide and iodoacetamide are the most cytotoxic. We discuss I-DBP formation mechan...