•The removal of 5 neonicotinoids by UV irradiation, UV/H2O2 and UV/PS was investigated.•The quantum yields for the UV photolysis of neonicotinoids at 254 nm were determined.•The degradation rate of ...neonicotinoids followed pseudo-first order kinetics.•Indirect photolysis was important only for neonicotinoids with low quantum yield.•Natural organic matter and radical scavengers inhibited the removal of neonicotinoids.
Neonicotinoids are a new class of insecticides whose potential side-effects on the human health and the environment have not yet been well investigated. Recently, the EU approved the Decision 2015/495 establishing a watch list of substances for Union-wide monitoring in the field of water policy, which includes five neonicotinoids: thiamethoxam (TMX), imidacloprid (ICP), clothianidin (CTD), thiacloprid (TCP) and acetamiprid (AMP). The photodegradation of neonicotinoids by monochromatic UV irradiation (254 nm) has been investigated. The photolysis rate followed pseudo-first order kinetics, with rate constant values depending on the nature of the specific compound, pH, and the presence or absence of radical scavengers. A method based on atrazine actinometry provided the following quantum yields at pH = 7: (77 ± 3) × 10−3, (43 ± 2) × 10−3, (48 ± 1) × 10−3, (17 ± 2) × 10−3 and (5 ± 2) × 10−3 mol E−1 for TMX, CTD, ICP, TCP and AMP, respectively. The effects of the presence of bicarbonate, nitrate, nitrite and chloride ions on the simultaneous photodegradation of nicotinoids were not very significant, and only the removal of AMP, the least photosensitive neonicotinoid, was negatively affected. However, the photodegradation of neonicotinoids was clearly inhibited by the addition of humic acids. The results obtained in experiments performed in the presence of hydrogen peroxide or persulfate indicated that while direct UV photolysis was the main degradation pathway for TMX and even for CTD, ICP and TCP, the contribution of indirect photolysis (radical pathway) was important in the case of pollutants with low values of quantum yield such as AMP. Although the presence of natural organic and inorganic matter in real water matrices decreased the degradation rate of the selected neonicotinoids, UV photolysis and the AOPs UV/H2O2 and UV/PS processes constitute efficient technologies for the removal of these pollutants from contaminated waters.
•The removal of 5 emerging contaminants (ECs) by UV/PS was investigated.•Rate constants of ECs with sulfate radicals were determined by competition kinetics.•The degradation rate of ECs followed ...pseudo-first order kinetics.•The maximum degradation rate was achieved at near neutral pH.•Natural organic matter and radical scavengers inhibited the removal of ECs.
The degradation of five selected emerging contaminants (ECs) including 1H-benzotriazole (BZ), N,N-diethyl-m-toluamide or DEET (DT), chlorophene (CP), 3-methylindole (ML), and nortriptyline hydrochloride (NH) in aqueous solutions by UV-activated persulfate (UV/PS) has been investigated. Selected ECs were not effectively degraded by direct UV photolysis or dark PS. However, their photodegradation efficiency significantly increased with addition of PS due to the generation of SO4− and HO. Second order rate constants for the reaction between SO4− and each EC were determined by competition kinetics, being the values at pH 7 2.0 × 1010, 1.2 × 1010, 1.8 × 109, 1.1 × 109 and 9.5 × 108 M−1 s−1 for NH, ML, CP, BZ and DT, respectively. While the dose of PS exerted a positive influence on the degradation of ECs, the highest degradation rate was observed at near neutral pH. With respect to the influence of background water matrix constituents, bicarbonate showed an inhibition effect on the removal of DT, BZ and NH and promoted the degradation of CP and especially of ML, which can be explained by their high reaction rate with carbonate radicals. The presence of humic acids inhibited the degradation of selected ECs, probably due to light screening and radical scavenging. Both radical species SO4− and HO exert an important role on the oxidation of the ECs investigated by the UV/PS system, being the contribution of SO4− predominant for those compounds that present high reactivity with this radical. Although the presence of inorganic and organic matter in real water matrices decreased the degradation rate of selected ECs, UV/PS process is an efficient option for their removal from contaminated waters.
The persistence in the environment and possible harmful effects of neonicotinoid insecticides have raised some concerns, which have led to the proposal of various measures for their remediation. The ...aim of this work was to study the elimination of five neonicotinoids (thiamethoxam (THM), imidacloprid (IMI), clothianidin (CLO), thiacloprid (THC), and acetamiprid (ACE)) using ferrate (Fe(VI)) as the oxidizing agent. Firstly, second-order rate constants for the reactions of neonicotinoids with Fe(VI) were determined at different pHs. The most reactive compound was THC, with a rate constant of 400 ± 43 M
−1
s
−1
at pH 8 (the optimum pH considering the predominance of the most reactive species (HFeO
4
−
) and the decreasing self-decomposition of Fe(VI) with pH), followed by CLO (10.7 ± 1.7 M
−1
s
−1
), THM (9.7 ± 0.7 M
−1
s
−1
), and IMI (2.5 ± 0.6 M
−1
s
−1
). ACE did not significantly react with Fe(VI). The oxidation of the selected pollutants in secondary effluents by Fe(VI) was rather slow, and only THC could be efficiently removed. The presence of natural organic matter (NOM) exerted a negative influence on the removal of the neonicotinoids of moderate reactivity with Fe(VI) (CLO, THM, and IMI). The additional presence of peroxymonosulfate (Fe(VI)/PMS system) slightly increased the removal of neonicotinoids due to the formation of hydroxyl and sulfate radicals. Finally, the application of the Fe(VI)/sulfite system considerably increased the oxidation rate of the selected pollutants, with enhanced formation of hydroxyl and, especially, sulfate radicals. Overall, these results suggest that the Fe(VI)/sulfite system has significant potential to address environmental and health concerns associated with neonicotinoids in water sources with low NOM content.
Graphical abstract
•Ozone exhibited better pollutants and UV254 removal than chlorine and permanganate.•0.5mgO3mgDOC−1 led to an important elimination of fast ozone-reacting compounds.•Iron coagulation was more ...efficient than alum and removed high MW compounds.•PAC could effectively eliminate hydrophobic and aromatic contaminants.•Coupling coagulation with ozone significantly improved contaminants and EfOM removal.
One important disadvantage of using ultrafiltration (UF) and nanofiltration (NF) for reclamation of secondary effluents from municipal wastewater treatment plants (WWTPs) is the necessity to dispose of the UF and NF retentates. Different advanced treatments including coagulation (iron and alum), oxidation (chlorine, permanganate and ozone) and powdered activated carbon (PAC) adsorption were compared for their efficiencies in removing 11 selected micropollutants and effluent organic matter (EfOM) from UF and NF retentates generated in the filtration of secondary effluents. Ozone exhibited better micropollutants and UV254 removal efficiencies than chlorine and permanganate. Similar abatement of organics was observed when the same specific oxidant dose was applied to UF and NF retentates. Coagulation preferentially removed high molecular weight compounds, being ineffective for the elimination of most micropollutants. In general terms, iron coagulation was more efficient than alum, since iron achieved higher DOC and UV254 removal at lower molar doses. In addition, PAC was an effective method for removing micropollutants, especially hydrophobic and aromatic compounds. The hybrid coagulation/ozonation process improved micropollutants and EfOM (DOC and UV254) removal. A specific ozone dose of 1mgO3mgDOC−1 was able to almost completely remove selected micropollutants from the UF retentate. The final effluent, which is likely more biodegradable and less toxic, could be recirculated to biological treatment processes in the WWTP, avoiding the continuous discharge of non-biodegradable micropollutants through the WWTP effluents.
The photolysis of five frequent emerging contaminants (Benzotriazole, Chlorophene, N,N-diethyl-m-toluamide or DEET, Methylindole, and Nortriptyline HCl) was investigated in ultrapure water under ...monochromatic ultraviolet radiation at 254 nm and by a combination of UV and hydrogen peroxide. The results revealed that the photolysis rates followed first-order kinetics, with rate constant values depending on the nature of the specific compound, the pH, and the presence or absence of the scavenger tert-butanol. Quantum yields were also determined and values in the range of 53.8 × 10−3 − 9.4 × 10−3 mol E−1 for Benzotriazole, 525 × 10−3 − 469 × 10−3 mol E−1 for Chlorophene, 2.8 × 10−3 − 0.9 × 10−3 mol E−1 for DEET, 108 × 10−3 − 165 × 10−3 mol E−1 for Methylindole, and 13.8 × 10−3 − 15.0 × 10−3 mol E−1 for Nortriptyline were obtained. The study also found that the UV/H2O2 process enhanced the oxidation rate in comparison to direct photolysis. High-performance liquid chromatography coupled to electrospray ionization quadrupole time-of-flight mass spectrometry (HPLC-ESI-QTOF-MS) technique was applied to the concentrations evaluation and further identification of the parent compounds and their by-products, which allowed the proposal of the degradation pathways for each compound. Finally, in order to assess the aquatic toxicity in the photodegradation of these compounds, the Vibrio fischeri acute toxicity test was used, and the results indicated an initial increase of this parameter in all cases, followed by a decrease in the specific case of Benzotriazole, DEET, Methylindole, and Chlorophene.
► Photolysis of five emerging contaminants (EC) was investigated. ► First-order rate constants and quantum yields were determined for each EC. ► The combined UV/H2O2 process provided a significant increase in the reaction rates. ► Intermediates were identified and the degradation pathways were proposed. ► Toxicity measurements showed an initial increase, followed by a decrease.
As the World Health Organization (WHO) progresses with provisional Drinking Water Guidelines of 1
μg/L for microcystin-LR and a proposed Guideline of 1
μg/L for cylindrospermopsin, efficient ...treatment strategies are needed to prevent cyanotoxins such as these from reaching consumers. A kinetic database has been compiled for the oxidative treatment of three cyanotoxins: microcystin-LR (MC-LR), cylindrospermopsin (CYN), and anatoxin-a (ANTX) with ozone, chlorine, chlorine dioxide and permanganate. This kinetic database contains rate constants not previously reported and determined in the present work (e.g. for permanganate oxidation of ANTX and chlorine dioxide oxidation of CYN and ANTX), together with previously published rate constants for the remaining oxidation processes. Second-order rate constants measured in pure aqueous solutions of these toxins could be used in a kinetic model to predict the toxin oxidation efficiency of ozone, chlorine, chlorine dioxide and permanganate when applied to natural waters. Oxidants were applied to water from a eutrophic Swiss lake (Lake Greifensee) in static-dose testing and dynamic time-resolved experiments to confirm predictions from the kinetic database, and to investigate the effects of a natural matrix on toxin oxidation and by-product formation. Overall, permanganate can effectively oxidize ANTX and MC-LR, while chlorine will oxidize CYN and MC-LR and ozone is capable of oxidizing all three toxins with the highest rate. The formation of trihalomethanes (THMs) in the treated water may be a restriction to the application of sufficiently high-chlorine doses.
•The removal of 11 emerging contaminants (ECs) by MEUF was investigated.•Cationic surfactants improved the removal of hydrophobic and anionic ECs.•CPC provided the highest contaminants removal and ...permeate flux.•Dissolved organic matter exerted a slight influence on ECs removal.•MEUF can be optimized for the selective removal of ECs from different effluents.
The removal of 11 selected emerging contaminants (ECs, acetaminophen, metoprolol, caffeine, antipyrine, sulfamethoxazole, flumequine, ketorolac, atrazine, isoproturon, 2-hydroxybiphenyl and diclofenac) by micellar-enhanced ultrafiltration (MEUF) has been investigated. Anionic sodium dodecylsulfate (SDS), non-ionic surfactants Triton X-100 (TX-100) and Tween 20 (TW-20), and cationic surfactants cetylpyridinium chloride (CPC) and cetyl trimethyl ammonium bromide (CTAB) were used. The retention coefficients of the selected compounds were determined in order to evaluate the separation efficiency of ECs from surfactant micelles. It was found that cationic surfactants were more appropriated for the removal of negatively charged and hydrophobic ECs. However, the presence of surfactant decreased the permeate flux due to the concentration polarization and membrane fouling. Among surfactants, the best results in terms of lower membrane fouling and higher retention of ECs were obtained with CPC. In addition, the effects of the MWCO of UF membranes and the water matrix on ECs and CPC removal and on membrane fouling were also evaluated. The increase of the feed CPC concentration improved the removal of ECs, although the permeate flux decreased. The removal of ECs and CPC was not affected by trans-membrane pressure. According to these results, solubilisation of ECs in the micelles and retention of the micelles by the membrane govern the overall retention process.
Organic micropollutants (OMPs) present in water and wastewater are in the spotlight because of their potentially harmful effects even at low concentrations and the difficulties of their elimination ...in urban wastewater treatment plants (UWWTPs). This study explores the impact of some membrane filtration processes on the removal of a group of 11 OMPs with an eye on the effects of two pretreatments (i.e., coagulation and adsorption onto powdered activated carbon (PAC)) and the adsorption of OMPs onto the membranes on the overall removal. For this purpose, ultrafiltration (UF) and nanofiltration (NF) experiments were conducted with selected OMPs spiked in ultrapure water and secondary effluents from UWWTPs. It was observed that the adsorption of OMPs onto the membranes was influenced by the characteristics of the membranes, as well as the presence of effluent organic matter (EfOM). Since adsorption was the dominant mechanism for the rejection of OMPs by UF membranes, a study of the adsorption equilibrium of the micropollutants using UF membrane pieces as the adsorbent was conducted. The adsorption isotherms for the most hydrophobic OMPs fitted the Langmuir model. The efficiency of coagulation and powdered activated carbon (PAC) adsorption coupled with UF were also investigated. Both pretreatments alleviated membrane fouling and improved the rejection of organic and inorganic matter. The PAC pretreatment significantly improved the removal of OMPs in the combined PAC/UF process. The best options for achieving reclaimed water with satisfactory physicochemical quality, nearly devoid of OMPs and microorganisms, and suitable for diverse reuse purposes are either the NF treatment or the combination of PAC/UF.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Halophenols are often reported as off-flavor causing compounds responsible for medicinal taste and odor episodes in drinking water. To better understand and minimize the formation of 2-bromophenol ...and 2,6-dibromophenol which have low odor threshold concentrations (OTCs, 30 and 0.5
ng/L, respectively) a kinetic data base for the chlorination and bromination of phenols was established by combination of kinetic measurements and data from literature.
Second-order rate constants for the reactions of chloro- and bromophenols with chlorine and bromine were determined over a wide pH range. The second-order rate constants for bromination of phenols are about three orders of magnitude higher than for chlorination. A quantitative structure activity relationship (QSAR) showed a good comparability of second-order rate constants from this study with those published previously for different phenol derivatives. The quantification of product distribution of the formed halophenols demonstrated that chlorine or bromine attack in ortho position is favored with respect to the para position. A kinetic model was formulated allowing us to investigate the influence of chlorine dose and some water quality parameters such as the concentration of phenol, ammonia, bromide and the pH on the product distribution of halophenols.
The kinetic model can be applied to optimize drinking water chlorination with respect to phenol-born taste and odor problems. In general, high chlorine doses lead to low concentrations of intermediate odorous chlorophenols and bromophenols. An increase in the ammonia or phenol concentration leads to a higher consumption of HOCl and therefore greater final concentration of intermediate bromophenols. The presence of higher bromide than phenol concentration also facilitates the rapid bromination pathway which leads to further bromination of 2,6-dibromophenol to higher brominated phenols. Laboratory-scale experiments on taste and odor formation due to the chlorination of phenol- and bromide-containing waters have confirmed the trend of the model calculations.
► The removal of eleven emerging contaminants by combined treatments was investigated. ► PAC pre-treatment decreased membrane fouling and improved the quality of the permeate. ► Pre-coagulation with ...Fe(III) was slightly more favorable than with Al(III). ► The combinations PAC/UF and UF/GAC led to a significant removal of contaminants.
The removal of eleven emerging contaminants (acetaminophen, metoprolol, caffeine, antipyrine, sulfamethoxazole, flumequine, ketorolac, atrazine, isoproturon, 2-hydroxybiphenyl and diclofenac) present in a WWTP effluent by applying several combined treatments has been investigated. These combinations were constituted by PAC adsorption and/or coagulation pre-treatments followed by UF, as well as by an UF treatment followed by GAC adsorption post-treatment. PAC pre-treatment decreased membrane fouling, with the advantage that PAC was separated from the final effluent in the UF step. Low PAC dose in the range 10–50mgL−1 in the adsorption pre-treatment was enough in order to remove most of the emerging contaminants and to partially improve water quality parameters. However, if the goal is to reach a high improvement of water quality parameters in the pre-treatment step, a PAC dose above 500mgL−1 was required. Although coagulation pre-treatment did not increase appreciably the permeate flux in the UF step, the final quality of the permeate was improved, especially when the combination Fe(III)/UF was applied. Finally, a significant positive effect of the GAC post-treatment after the UF treatment was appreciated, which led to an increase in the removal of the water quality parameters and a significant elimination of emerging contaminants.
