Real Water Matrices Research Articles

Paired electro-oxidation of insecticide imidacloprid and electrodenitrification in simulated and real water matrices

Groundwater is one of the main freshwater resources on the Earth, but its contamination by NO3− and pesticides jeopardizes its suitability for consumption. In this work, the simultaneous electro-oxidation of insecticide imidacloprid (IMC) and electroreduction of NO3− in softened groundwater containing a large amount of Cl− has been addressed. The assays were carried out in a stirred undivided tank reactor containing either a boron-doped diamond (BDD) or IrO2 anode, and Fe cathode, which showed greater electrocatalytic activity than stainless steel to reduce NO3−. Comparative assays in simulated water mimicking the anionic composition of groundwater were made to assess the influence of natural organic matter (NOM) on the decontamination process. The BDD/Fe cell had much greater performance than the IrO2/Fe one, although the former produced larger amounts of ClO3− and ClO4−. In all cases, the NO3−, Cl− and IMC decays agreed with a (pseudo)-first-order kinetics. In the BDD/Fe cell, total NO3− removal was reached at j ≥ 10 mA cm−2 in softened groundwater, at similar rate in the presence and absence of IMC, but it was decelerated using the simulated matrix. The N-products formed upon NO3− electroreduction contributed to IMC degradation, but its decay was inhibited by NOM because of the partial consumption of oxidants like hydroxyl radical and active chlorine. Operating at 5 mA cm−2 for 240 min, total removal of the insecticide and 61.5% total organic carbon (TOC) decay were achieved, also attaining a low NO3− content that was suitable for humans. Eight heteroaromatic products were identified, allowing the proposal of a reaction sequence for IMC degradation in groundwater.

Photodegradation behaviour of multiclass ultraviolet filters in the aquatic environment: Removal strategies and photoproduct identification by liquid chromatography–high resolution mass spectrometry

Different photodegradation strategies were assessed to remove 21 multiclass organic ultraviolet (UV) filters including benzophenone-, camphor-, and p-aminobenzoic acid- derivatives, methoxycinnamates, and salicylates, among others, from the aquatic environment. Direct photolysis under UVA (λ = 365 nm) and UVC (λ = 254 nm) radiations and advanced oxidation processes (AOPs) based on heterogeneous UVA/TiO2 photocatalysis and the UVC/H2O2 system were applied for the degradation tests. LC–MS/MS and SPME-GC–MS/MS were employed for the monitoring of the target compound degradations. UVC photolysis provided the highest removal efficiency for most of the studied UV filters with degradation yields higher than 90% after 60 min of light exposure in ultrapure water. This radiation was also applied to different real water matrices (river, sea, and swimming-pool water), showing that the degradation yield was dependent on the water matrix, being more difficult the removal of the target compounds in waters with high organic matter content. In an attempt to accelerate the degradation of the studied compounds in this kind of water matrices, the use of a powerful UVC/H2O2 system improvement the reaction kinetics, showing degradation > 90% for most of the studied UV filters. Besides, up to 19 photoproducts could be identified by HRMS.

Effects of water matrices on the degradation of naproxen by reactive radicals in the UV/peracetic acid process

The UV/peracetic acid (UV/PAA) process as a novel advanced oxidation process has been reported to produce carbon-centered radicals (RC•) for Naproxen (NAP) degradation, which is a representative of naphthyl structure substances. Real water matrices, such as carbonate and bicarbonate ions (CO32−/HCO3−), humic acid (HA), and chloride ion (Cl−), may react with these reactive radicals and change their contributions to NAP degradation. The results showed that RC• contributed 60.8% and •OH contributed 39.2% to NAP degradation in pure water by a competition method. CO32−/HCO3− (0–20 mM) showed minimal effect on NAP degradation in the UV/PAA process, meanwhile, it has observable inhibition effect on NAP degradation in the UV/H2O2 process (mainly of •OH) and minimal effect in the UV/PAA process with tert-butanol (TBA) (mainly of RC•). Results suggested that CO32−/HCO3− could react with •OH yielding CO3•- with low reactivity to NAP, CO3•- could further react with PAA to produce RC•. This speculation was confirmed by the increased contribution of RC• to NAP degradation with the increase of CO32−/HCO3− concentration through the competition method. HA (0–5 mg/L) had a higher scavenging capacity for RC• than •OH because HA with naphthyl structure was likely to be attacked by RC•. Cl− (0–200 mM) had little effect on NAP degradation in the UV/PAA and UV/H2O2 processes, while exerted an observable inhibition on NAP degradation in the UV/PAA process with TBA. This finding suggested that Cl− could react with RC• to produce Cl•, which could further convert into HOCl•-, and then excess •OH was formed. The new knowledge on the conversion of reactive radicals obtained in this study provides an important basis for facilitating further research on the UV/PAA advanced oxidation.

Enhanced removal of arsenite and arsenate by a multifunctional Fe-Ti-Mn composite oxide: Photooxidation, oxidation and adsorption

In order to attain a high-efficiency and low-cost adsorbent for both arsenate (As(V)) and arsenite (As(III)) removal from As-contaminated water, a novel nanostructured Fe-Ti-Mn composite oxide (FTMO) was fabricated through a one-step simultaneous oxidation and co-precipitation method. Batch control experiments and series of spectroscopy detection technologies were carried out to investigate the surface change of the FTMO adsorbent and the respective role of Fe, Ti and Mn content in the arsenic adsorption process. The results showed that the FTMO adsorbent had a high adsorption capacity for both As(V) and As(III) (especially for the latter one) via the formation of inner-sphere complexes at the water/oxide interface under both darkness and light conditions. The material could effectively oxidize As(III) to As(V) and light illumination could further apparently enhance the As(III) oxidation, thus achieving high adsorption efficiency of As(III). Combined with the characterizations from FTIR, ESR and XPS, it was assumed that the predominant As(III) removal mechanism could be attributed to the coupling of various processes including photooxidation, oxidation and adsorption. The Ti and Mn contents were dominant for the As(III) oxidation, while the Fe content mainly played an important role for the adsorption of newly formed As(V). However, the involvement of surface hydroxyl groups and the formation of inner-sphere surface complexes were primarily responsible for the As(V) adsorption mechanism. Moreover, the successful removal of arsenic from real water matrices made the FTMO a potentially attractive adsorbent for both As(V) and As(III) removal.

Degradation of neonicotinoids by UV irradiation: Kinetics and effect of real water constituents

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.

Accelerated Oxidation of Organic Contaminants by Ferrate(VI): The Overlooked Role of Reducing Additives.

This paper presents an accelerated ferrate(VI) (FeVIO42-, FeVI) oxidation of contaminants in 30 s by adding one-electron and two-electron transfer reductants (R(1) and R(2)). An addition of R(2) (e.g., NH2OH, AsIII, SeIV, PIII, and NO2-, and S2O32-) results in FeIV initially, while FeV is generated with the addition of R(1) (e.g., SO32-). R(2) additives, except S2O32-, show the enhanced oxidation of 20-40% of target contaminant, trimethoprim (TMP). Comparatively, enhanced oxidation of TMP was up to 100% with the addition of R(1) to FeVI. Interestingly, addition of S2O32- (i.e., R(2)) also achieves the enhanced oxidation to 100%. Removal efficiency of TMP depends on the molar ratio ([R(1)]:[FeVI] or [R(2)]:[FeVI]). Most of the reductants have the highest removal at molar ratio of ∼0.125. A FeVI-S2O32- system also oxidizes rapidly a wide range of organic contaminants (pharmaceuticals, pesticides, artificial sweetener, and X-ray contrast media) in water and real water matrices. FeV and FeIV as the oxidative species in the FeVI-S2O32--contaminant system are elucidated by determining removal of contaminants in oxygenated and deoxygenated water, applying probing agent, and identifying oxidized products of TMP and sulfadimethoxine (SDM) by FeVI-S2O32- systems. Significantly, elimination of SO2 from sulfonamide (i.e., SDM) is observed for the first time.

Modeling emerging contaminants breakthrough in packed bed adsorption columns by UV absorbance and fluorescing components of dissolved organic matter

This study investigated, using rapid small-scale column testing, the breakthrough of dissolved organic matter (DOM) and eleven emerging organic contaminants (EOCs) during granular activated carbon (GAC) filtration of different water qualities, including wastewater, surface water and synthetic water (riverine organic matter dissolved in deionized water). Fluorescing organic matter was better adsorbed than UV absorbance at 254 nm (UV254) and dissolved organic carbon (DOC) in all tested water. Furthermore, highest adsorption of DOM (in terms of DOC, UV254 and fluorescence) was observed during wastewater filtration. UV absorbing DOM had fast and similar breakthrough in surface water and synthetic water, whereas fluorescence breakthrough was very rapid only in synthetic water. PARAFAC modeling showed that different fluorescing components were differently adsorbed during GAC process. Particularly, fluorescing components with maxima intensity at higher excitation wavelengths, which are corresponding to humic-like fluorescence substances, were better removed than other components in all waters. As opposed to DOM, EOCs were better adsorbed during synthetic water filtration, whereas the fastest EOCs breakthrough was observed during filtration of wastewater, which was the water that determined the highest carbon fouling. Exception was represented by long-chained perfluoroalkylated substances (i.e., PFOA, PFDA and PFOS). Indeed, adsorption of these compounds resulted independent of water quality. In this study was also investigated the applicability of UV254 and fluorescing PARAFAC components to act as surrogates in predicting EOCs removal by GAC in different water matrices. Empirical linear correlation for the investigated EOCs were determined with UV254 and fluorescing components in all water qualities. However, fluorescence measurements resulted more sensitive than UV254 to predict EOC breakthrough during GAC adsorption. When the data from all water qualities was combined, good correlations between the microbial humic-like PARAFAC component and EOC removals were still observed and they resulted independent of water quality if considering only real water matrices (wastewater and surface water). On the contrary, correlations between EOC removals and UV254 removals were independent of water quality when combining data of surface waters and synthetic water, but a different correlation model was needed to predict EOCs breakthrough in wastewater.

Efficient cephalexin degradation using active chlorine produced on ruthenium and iridium oxide anodes: Role of bath composition, analysis of degradation pathways and degradation extent

The elimination of cephalexin (CPX) using electro-generated Cl2-active on Ti/RuO2-IrO2 anode was assessed in different effluents: deionized water (DW), municipal wastewater (MWW) and urine. Single Ti/RuO2 and Ti/IrO2 catalysts were prepared to compare their morphologies and electrochemical behavior against the binary DSA. XRD and profile refinement suggest that Ti/RuO2-IrO2 forms a solid solution, where RuO2 and IrO2 growths are oriented by the TiO2 substrate through substitution of Ir by Ru atoms within its rutile-type structure. SEM reveals mud-cracked structures with flat areas for all catalysts, while EDS analysis indicates atomic ratios in the range of the oxide stoichiometries in the nominal concentrations used during synthesis. A considerably higher CPX degradation is achieved in the presence of NaCl than in Na2SO4 or Na3PO4 media due to the active chlorine generation. A faster CPX degradation is reached when the current density is increased or the pH value is lowered. This last behavior may be ascribed to an acid-catalyzed reaction between HClO and CPX. Degradation rates of 22.5, 3.96, and 0.576 μmol L−1 min−1 were observed for DW, MWW and urine, respectively. The lower efficiency measured in these last two effluents was related to the presence of organic matter and urea in the matrix. A degradation pathway is proposed based on HPLC-DAD and HPLC-MS analysis, indicating the fast formation (5 min) of CPX-(S)-sulfoxide and CPX-(R)-sulfoxide, generated due the Cl2-active attack at the CPX thioether. Furthermore, antimicrobial activity elimination of the treated solution is reached once CPX, and the initial by-products are considerably eliminated. Finally, even if only 16% of initial TOC is removed, BOD5 tests prove the ability of electro-generated Cl2-active to transform the antibiotic into biodegradable compounds. A similar strategy can be used for the abatement of other recalcitrant compounds contained in real water matrices such as urine and municipal wastewaters.

Characterization of seven psychoactive pharmaceuticals as N‐nitrosodimethylamine precursors during free chlorine and chlorine dioxide chlorination processes

AbstractBACKGROUNDPsychoactive pharmaceuticals used to treat neurological disorders are of great concern because of their frequent detection in the aquatic environment and drinking water. The possibility for concurrent formation of N‐nitrosodimethylamine (NDMA) from psychoactive pharmaceuticals during disinfection is still not well‐studied. In the present study, seven widely used psychoactive drugs were selected due to their possession of a DMA functional group. The NDMA formation potentials of the selected drugs were assessed during free chlorine (NaOCl) and chlorine dioxide (ClO2) disinfection processes. The influence of several parameters (i.e. disinfectant dose, pH and water matrix) was investigated to better understand the reaction between the drugs and disinfectants that cause the formation of NDMA.RESULTSThe NDMA molar yields of seven pharmaceuticals were higher than 2%. NDMA formation was independent of the pH value, and more NDMA formation was observed during free chlorine chlorination. NDMA generation was enhanced when the selected pharmaceuticals were present in real water matrices, especially in secondary effluent.CONCLUSIONThis study demonstrated that the seven selected psychoactive pharmaceuticals containing dimethylamine groups can serve as NDMA precursors during free chlorine and chlorine dioxide chlorination processes. ClO2 was a proper disinfectant for controlling NDMA formation during chlorination. © 2018 Society of Chemical Industry

The role of operating parameters and irradiation on the electrochemical degradation of tetracycline on boron doped diamond anode in environmentally relevant matrices

AbstractBACKGROUNDNowadays, due to the inappropriate use of antibiotics, significant quantities have been detected in environmental samples. Therefore there is a need for a technology to eliminate the accumulation of pharmaceuticals in receiving water bodies. In recent years electrochemical oxidation showed superior efficiency for the purification of water from pharmaceuticals.RESULTSboron doped diamond (BDD) showed better efficiency than platinum electrode and stainless steel for the degradation of 500 µg L−1 tetracycline (TC) with 0.1 mol L−1·Na2SO4. The presence of 200 mg L−1 bicarbonates decreased the apparent kinetic constant from 0.328 to 0212 min−1. Instead, the addition of 200 mg L−1 NaCl increased the kinetic constant by almost four times, while the presence of 10 mg L−1 of humic acid decreased the kinetic constant by 18%. The process was favored in real environmental matrices like bottled water and wastewater in comparison with ultrapure water. The use of BDD as both anode and cathode enhanced the efficiency by almost 20%. The presence of UVA or solar radiation increased the decomposition of tetracycline by 14%. Changes in toxicity to Vibrio fisheri bacteria during treatment of TC in the secondary effluent are mainly attributed to the formation of intermediates of the water matrix itself and does not follow the TC removal.CONCLUSIONSElectrochemical oxidation was favored for removal of TC in real water matrices due to the presence of chlorides. The use of BDD as both anode and cathode with simultaneous solar irradiation is a promising technology for water remediation from TC. © 2018 Society of Chemical Industry

Persulfate-based photodegradation of a beta-lactam antibiotic amoxicillin in various water matrices

ABSTRACTAmoxicillin (AMX), a widely used beta-lactam antibiotic, belongs to the World Health Organization’s list of essential medicines. This subsequently causes its long-term presence in the environment and therefore, affects different environmental compartments. In this research, the degradation and mineralisation of AMX by UVC-activated persulfate-based treatment in various aqueous media was assessed. The degradation of the target compound was in accordance with the pseudo-first-order reaction kinetics in all the UVC-induced systems. The results indicated that AMX degradation in any real water matrices is notably inhibited by the matrix properties. The trials with radical scavengers in ultrapure water proved the existence of and HO., but mainly contributed to the degradation of AMX in the UVC/ and UVC//Fe2+ systems. It was shown that the parent compound disappeared during the treatment, but the mineralisation extent referred to the formation of transformation products the main of which were identified. The findings of this study could provide valuable information about the elimination of beta-lactam antibiotics from various environmental and processed waters.

The electro-peroxone process for the abatement of emerging contaminants: Mechanisms, recent advances, and prospects

The electro-peroxone (E-peroxone) process is an emerging electrochemical advanced oxidation process (EAOP) that combines ozonation with in situ cathodic hydrogen peroxide (H2O2) production to drive the peroxone reaction for water and wastewater treatment. Over the past several years, the E-peroxone process has quickly emerged as a promising EAOP for the abatement of emerging contaminants (ECs) in water. Because of the enhanced ozone (O3) transformation to hydroxyl radicals (OH) by electro-generated H2O2, the E-peroxone process can considerably increase the efficiency and decrease the energy demand for the abatement of ozone-resistant ECs compared with conventional ozonation. Meanwhile, the E-peroxone process can substantially mitigate the formation of bromate during the treatment of bromide-containing water, which has been a major concern of conventional ozonation for water treatment. Hence, by simply installing electrodes in ozone contactors, the E-peroxone process can remarkably enhance the performance of water and wastewater treatment in various aspects. Compared with other ozone-based AOPs such as the conventional peroxone (O3/H2O2) and UV/O3 processes, the E-peroxone process also represents a more convenient, cost-effective, energy-efficient, and safer option for EC abatements. This paper reviews recent research of the E-peroxone process, with focus on the abatement of ECs in real water matrices. The fundamental reaction mechanisms that are essential to the understanding, design, and operation of the E-peroxone process are described. The abatement of various ECs in natural water and wastewater by the E-peroxone process are critically reviewed. The challenges in scaling-up the E-peroxone process and integrating it in water and wastewater treatment trains for practical applications are discussed.

Transformation of methylparaben during water chlorination: Effects of bromide and dissolved organic matter on reaction kinetics and transformation pathways

The reaction kinetics, products, and pathways of methylparaben (MeP) during water chlorination with and without bromide (Br−) were investigated to better understand the fate of parabens in chlorinated waters. During the chlorination of MeP-spiked waters without Br−, MeP was transformed into mono-Cl-MeP and di-Cl-MeP with apparent second-order rate constants (kapp) of 64M−1s−1 and 243M−1s−1 at pH7, respectively, while further chlorination of di-Cl-MeP was relatively slower (kapp=1.3M−1s−1 at pH7). With increasing Br− concentration, brominated MePs, such as mono-Br-MeP, Br-Cl-MeP, and di-Br-MeP, became major transformation products. The di-halogenated MePs (di-Cl-MeP, Br,Cl-MeP, and di-Br-MeP) showed relatively low reactivity to chlorine at pH7 (kapp=1.3–4.6M−1s−1) and bromine (kapp=32–71M−1s−1), which explains the observed high stability of di-halogenated MePs in chlorinated waters. With increasing pH from 7 to 8.5, the transformation of di-halogenated MePs was further slowed due to the decreasing reactivity of di-MePs to chlorine. The formation of the di-halogenated MePs and their further transformation become considerably faster at Br− concentrations higher than 0.5μM (40μg/L). Nonetheless, the accelerating effect of Br− diminishes in the presence of dissolved organic matter (DOM) extract (Suwannee River humic acid (SRHA)) due to a more rapid consumption of bromine by DOM than chlorine. The effect of Br− on the fate of MeP was less in the tested real water matrices, possibly due to a more rapid bromine consumption by the real water DOM compared to SRHA. A kinetic model was developed based on the determined species-specific second-order rate constants for chlorination/bromination of MeP and its chlorinated and brominated MePs and the transformation pathway information, which could reasonably simulate the transformation of MePs during the chlorination of water in the presence of Br− and selected DOM.

Simultaneous determination of trace levels of multiclass fungicides in natural waters by solid - phase microextraction - gas chromatography-tandem mass spectrometry

A solvent-free method based on solid-phase microextraction (SPME) followed by gas chromatography-tandem mass spectrometry (GC-MS/MS) has been developed for the simultaneous determination of eleven fungicides at trace levels in different types of waters. Several experimental SPME parameters such as temperature, fibre coating, and SPME mode, were optimized in order to obtain the highest extraction efficiency. Under the optimal conditions, 100 °C, polyacrilate fibre (PA) and direct-immersion mode, the method was validated showing good linearity, repeatability and reproducibility. Recovery studies were carried out in four different real water matrices and at three concentration levels (20, 200 and 2000 ng L−1), with overall recovery values between 92 and 104% and relative standard deviations (RSD) about 10%. Limits of detection (LODs) at the low ng L−1 were obtained. The method demonstrated its suitability for the determination of fungicides in real water samples using external calibration for quantification purposes as well as for photodegradation studies at low concentration levels.

Effect of preconditioning on silver leaching and bromide removal properties of silver-impregnated activated carbon (SIAC)

Silver impregnated activated carbon (SIAC) has been found to be effective in mitigating the formation of brominated-disinfection by products during drinking water treatment. However, there are still uncertainties regarding its silver leaching properties, and strategies for the prevention of silver leaching have remained elusive. This study focused on the evaluation of one type of commercially available SIAC for its ability to remove bromide while minimising silver leaching from the material. Both synthetic and real water matrices were tested. Depending on solution pH, it was found that changing the surface charge properties of SIAC, as measured by the point of zero charge pH, can result in additional bromide removal while minimising the extent of silver leaching. To better understand the mechanism of silver leaching from the SIAC, eight preconditioning environments, i.e. variable pH and ionic strength were tested for a fixed amount of SIAC and two preconditioning environments were selected for a more detailed investigation. Experiments carried out in synthetic water showed that preconditioning at pH 10.4 did not deteriorate the capacity of SIAC to remove bromide, but significantly decreased the release of silver in the form of ionic silver (Ag+), silver bromide (AgBr) and silver chloride (AgCl) from 40% for the pristine to 3% for the treated SIAC. This was confirmed using a groundwater sample. These results suggest that preconditioned SIAC has the potential to be an effective method for bromide removal with minimised silver leaching in a long-term field application for drinking water production.

Degradation of selected emerging contaminants by UV-activated persulfate: Kinetics and influence of matrix constituents

Abstract 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.

Specific and total N-nitrosamines formation potentials of nitrogenous micropollutants during chloramination

N-nitrosamines are a group of potent human carcinogens that can be formed during oxidative treatment of drinking water and wastewater. Many tertiary and quaternary amines present in consumer products (e.g., pharmaceuticals, personal care and household products) are known to be N-nitrosodimethylamine (NDMA) precursors during chloramination, but the formation of other N-nitrosamines has been rarely studied. This study investigates the specific and total N-nitrosamine (TONO) formation potential (FP) of various precursors from nitrogen-containing micropollutants (chlorhexidine, metformin, benzalkonium chloride and cetyltrimethylammonium chloride) and tertiary and quaternary model amines (trimethyl amine, N,N-dimethylbutyl amine, N,N-dimethylbenzyl amine and tetramethyl ammonium). All the studied nitrogenous micropollutants displayed quantifiable TONO FP, with molar yields in the range 0.04–11.92%. However, the observed TONO pools constituted mostly of uncharacterized species, not included in US-EPA 8270 N-nitrosamines standard mix. Only the quaternary ammonium compound benzalkonium chloride showed quantifiable NDMA FP (0.56% molar yield), however, explaining only a minor fraction of the observed TONO FP. The studied model amines showed molar NDMA yields from 0.10% (trimethyl amine) to 5.05% (N,N-dimethylbenzyl amine), very similar to the molar TONO yields. The comparison of the FPs of micropollutants and model compounds showed that the presence of electron donating functional groups (such as a benzyl group) in tertiary and quaternary amine precursors leads to a higher formation of NDMA and uncharacterized N-nitrosamines, respectively. LC-qTOF screening of a list of proposed N-nitrosamine structures has enabled to identify a novel N-nitrosamine (N-nitroso-N-methyldodecylamine) from the chloramination of benzalkonium chloride. This finding supports the hypothesis that different functional groups in quaternary amines can act as leaving groups during chloramination and form differing N-nitrosamine structures at significant yield. Molar TONO yields determined for micropollutants were finally validated under experimental conditions closer to real water matrices, confirming their representativeness also for lower concentration ranges.

Removal of PhACs and their impacts on membrane fouling in NF/RO membrane filtration of various matrices

The removal of pharmaceutically active compounds (PhACs) by fouled nanofiltration (NF) and reverse osmosis (RO) membranes has been extensively studied. Investigations on the effects of PhACs on organic fouling or biofouling in the NF/RO membrane application are still lacking. In this study, NF/RO membranes were fed with both synthetic (SRNOM solution and synthetic wastewater containing pure culture inoculum) and real (secondary effluent) water matrices spiked with three PhACs to elucidate the impact of PhACs on membrane fouling in comparison with control experiments in the absence of PhACs. Results showed that the PhACs mitigated flux decline during NF/RO filtration of SRNOM solution. The total organic foulants on both membrane surfaces decreased in the presence of PhACs due to the increased negative charges of the membranes and the enhanced size and charge effects of PhAC–macromolecule complexes in SRNOM solution. PhACs appeared to inhibit cell growth in the early stages of biofouling, causing a decline in total biomass, and then induced cell lysis, releasing EPS to protect from chemical stress in the later stages of biofouling, especially protein-like materials, causing more severe biofouling. The alleviation of declines in flux and salt rejection during the filtration of secondary effluent were found in the presence of PhACs. Therefore, we hypothesized that organic fouling or early-stage biofouling occurred during 100h of filtration of secondary effluent. The decrease in PhAC retention was more obvious due to the higher ionic strength in the secondary effluent. This study may aid understanding of PhAC removal from various matrices and the effects of PhAC mixtures on membrane fouling by in practical NF/RO membranes applications.

Enhanced photocatalytic reduction of chromium (VI) by Cu-doped TiO 2 under UV-A irradiation

Abstract This paper describes the photocatalytic reduction of aqueous hexavalent chromium (Cr(VI)), a potential human carcinogen and genotoxin, by copper doped TiO2 (Cu-TiO2) prepared by the simple-evaporation and calcination of CuCl2 and TiO2, under UV-A irradiation in the absence of hole scavengers. The Cu-TiO2 prepared at a Cu to TiO2 mass ratio of 1.5:100 and a calcination temperature of 300 °C showed the fastest photocatalytic reduction of Cr(VI). The reduction by the Cu-TiO2 followed pseudo-first order reaction kinetics, and its rate was twice as fast as that of unmodified TiO2 at pH 3. The Cu-TiO2 reached its maximum Cr(VI) reduction rate at pH 5, producing steady state hydrated electron concentrations ([e−]ss) 3.3 times higher than those by unmodified TiO2. The optimum working pH of the Cu-TiO2 is higher than that of many other photocatalysts. The XPS, XRD, TEM and SEM spectra all confirmed the incorporation of Cu into TiO2, and the BET analysis showed the similar surface areas of the Cu-TiO2 and unmodified TiO2. The enhanced reduction rate by the Cu-TiO2 was thus attributed to the reduced electron-hole recombination rate. More importantly, the Cr(VI) reduction rate by the Cu-TiO2 was only reduced by 20% with increasing alkalinity from 0 to 200 mg/L at pH 7, and it was not affected by the presence of NOM at concentrations up to 1 ppm. Lastly, the Cr(VI) reduction rate by the Cu-TiO2 was faster in tap water than in double deionized water. The wider working pH (optimum at pH 5), without addition of hole scavengers, and the faster reduction in tap water suggest the superior performance of the Cu-TiO2 photocatalyst in real water matrices.

Degradation pathways and organic matter transformation of acesulfame potassium electro-oxidation in real water matrices

Abstract This paper presents the pathways of acesulfame potassium (ACE-K) electro-degradation on a boron-doped diamond (BDD) electrode and the removal/mineralization of ACE-K in different environmental water matrices (biologically treated (hospital) wastewater (BTW), river water (RW), and ground water (GW)). The ACE-K was initially electrochemically transformed to an unknown compound ( m / z = 196) and then organic acids and inorganic compounds before mineralization. In the water matrices, ACE-K was completely degraded (pseudo-first-order apparent rate constants = (1.22‒2.25) × 10 −3 s −1 ). Before electrolysis, all ACE-K spiked solutions showed aromaticity (SUVA 254 ), while during electrolysis the variation of aromaticity was consistent with that of total organic carbon removal. The spike of ACE-K covered or lowered the intensities of fluorescence excitation-emission peaks in humic acid-like, aromatic protein I, and fulvic acid-like regions for BTW and those in soluble microbial by-product-like and tyrosine regions for RW and GW. After 120 min electrolysis, the ACE-K-associated fluorescence peaks disappeared but the original dissolved organic matter (DOM)-related ones slightly remained, so the removal/mineralization was harder for the DOM than for the ACE-K in the tested matrices. Electrolysis or spiking ACE-K increased the Microtox acute toxicity response in BTW.