Contaminants of emerging concern: a review of new approach in AOP technologies

CeO2 for Water Remediation: Comparison of Various Advanced Oxidation Processes

Three different Advanced Oxidation Processes (AOPs) have been investigated for the degradation of the imidacloprid pesticide in water: photocatalysis, Fenton and photo-Fenton reactions. For these tests, we have compared the performance of two types of CeO2, employed as a non-conventional photocatalyst/Fenton-like material. The first one has been prepared by chemical precipitation with KOH, while the second one has been obtained by exposing the as-synthetized CeO2 to solar irradiation in H2 stream. This latter treatment led to obtain a more defective CeO2 (coded as “grey CeO2”) with the formation of Ce3+ sites on the surface of CeO2, as determined by Raman and X-ray Photoelectron Spectroscopy (XPS) characterizations. This peculiar feature has been demonstrated as beneficial for the solar photo–Fenton reaction, with the best performance exhibited by the grey CeO2. On the contrary, the bare CeO2 showed a photocatalytic activity higher with respect to the grey CeO2, due to the higher exposed surface area and the lower band-gap. The easy synthetic procedures of CeO2 reported here, allows to tune and modify the physico-chemical properties of CeO2, allowing a choice of different CeO2 samples on the basis of the specific AOPs for water remediation. Furthermore, neither of the samples have shown any critical toxicity.

Tracing Urban Wastewater Contaminants into the Atlantic Ocean by Nontarget Screening

Oceans are the ultimate sink for many of the over 100 million man-made substances. Until now, monitoring was limited to a reduced number of targeted persistent organic pollutants, reaching open waters mainly via atmospheric deposition. However, the composition and fate of the thousands of pollutants reaching the marine environment though wastewater discharges from coastal sources remain largely unexplored. By combining a newly developed nontarget screening (NTS) workflow and high-resolution mass spectrometry (HRMS), we have identified over 500 sewage-derived contaminants occurring in the ocean. Samples from the NE Atlantic contained this anthropogenic imprint at distances over 50 km from the coastline and >500 m depth, beyond the continental margin. The range of identified compounds spans from pharmaceuticals and personal care products to food additives and industrial chemicals, including several that have never been reported in the environment, as they escaped conventional targeted analytical methods. Predicting the effects of the continuous input of this chemical "cocktail" on marine ecosystems is a formidable challenge, since 40% of the detected compounds lack information regarding their use and ecotoxicity.

Pig manure-derived nitrogen-doped mesoporous carbon for adsorption and catalytic oxidation of tetracycline

Ordered nitrogen-doped mesoporous carbon (NMC) was successfully synthesized with pig manure as the precursor. The resulting NMC materials exhibited excellent capacity of adsorption and potassium persulfate (PS) activation when used as catalysts for the oxidative degradation of tetracycline antibiotics (tetracycline hydrochloride (TH) as the target). For an initial TH concentration of 35 mg/L, the maximum adsorption capacity of NMC material prepared at 700 °C (NMC700) was 122.0 mg/g, and the degradation efficiency in the PS reaction system was 94.8% within 120 min. Investigation of the mechanism indicated that the NMC700 material with specific surface area (SSA) of 275.5 m²/g and 0.7% graphitic N content, provided a large amount of active sites for adsorption and catalytic oxidation of TH. Based on the results of selective degradation and electron paramagnetic resonance (EPR) experiments, a non-radical pathway for the degradation of pollutants was proposed. Chronoamperometry evaluation also supported the conclusion that the NMC material enhanced electron transfer to activate persulfate, accelerating the removal of TH.

Targeted profiling of chlorinated transformation products and the parent micropollutants in the aquatic environment: A comparison between two coastal cities

This study investigated chlorinated transformation products (TPs) and their parent micropollutants, aromatic pharmaceuticals and personal care products (PPCPs) in the urban water bodies of two metropolitan cities. Nine PPCPs and 16 TPs were quantitatively or semi-quantitatively determined using isotope dilution techniques and liquid chromatography-tandem mass spectrometry. TPs and most PPCPs were effectively removed by conventional wastewater treatments in a wastewater treatment plant (WWTP). Chlorinated parabens and all PPCPs (at concentrations below 1000 ng/L) were present in the waters receiving treated wastewater. By contrast, the waters receiving untreated wastewater contained higher levels of PPCPs (up to 9400 ng/L) and more species of chlorinated TPs including chlorinated parabens, triclosan, diclofenac, and bisphenol A. The very different chemical profiles between the water bodies of the two cities of similar geographical and climatic properties may be attributed to their respective uses of chemicals and policies of wastewater management. No apparent increase in the number of species or abundances of TPs was observed in either the chlorinated wastewater or the seawater rich in halogens. This is the first study to elucidate and compare the profiles of multiple TPs and their parent PPCPs in the water bodies of coastal cities from tropical islands. Our findings suggest that chlorinated derivatives of bisphenol A, diclofenac, triclosan, and parabens in the surface water originate from sources other than wastewater disinfection or marine chlorination. Although further studies are needed to identify the origins, conventional wastewater treatments may protect natural water bodies against contamination by those chlorinated substances.

Cellulose Acetate/P4VP-b-PEO Membranes for the Adsorption of Electron-Deficient Pharmaceutical Compounds

The prevalence of pharmaceutical compounds in surface and groundwater presents a rising threat to human health. As such, the search for novel materials that serve to avoid their release into the environment or for the remediation once in the water effluent is of utmost importance. The present work describes the fabrication of a cellulose acetate membrane modified with the block copolymer poly(4-vinylpyridine-b-ethylene oxide) (P4VP-b-PEO) crafted for the specific targeting and adsorption of electron-deficient pharmaceuticals (EDPs). The EDPs under study were sulfamethoxazole, sulfadiazine, and omeprazole. The results as part of this work present a thorough characterization of the prepared membranes by FTIR, contact angle measurement, and SEM images. Moreover, results show that the adsorptive character of the membrane correlates with the relative electron deficiency and spatial orientation of the contaminant. Interestingly, the addition of nominal 1% P4VP-b-PEO to the cellulose matrix helps to increase the adsorption efficiency of the membranes by at least 2-fold in most cases. For the compounds studied, the prepared membrane has a higher efficiency toward omeprazole followed by sulfamethoxazole and sulfadiazine. This work may serve to inspire the design and fabrication of selective soft materials for the adsorption and remediation of contaminants of emerging concern.

Improved Ozonation Efficiency for Polymerization Mother Liquid from Polyvinyl Chloride Production Using Tandem Reactors

Polymerization mother liquid (PML) is one of the main sources of wastewater in the chlor-alkali industry. The effective degradation of the PML produced in PVC polymerization using three or five ozone reactors in tandem was designed with a focus on improving the ozonation efficiency. The ozonation efficiency of the tandem reactors for the degradation of PML, along with the effect of ozone concentration, the number of reactors utilized in series, and the reaction time on the chemical oxygen demand (COD) removal were investigated in detail. The results showed that the COD removal increased as the ozone concentration was increased from 10.6 to 60 mg·L-1, achieving 66.4% COD removal at ozone concentration of 80.6 mg·L-1. However, when the ozone concentration was increased from 60 mg·L-1 to 80 mg·L-1, the COD removal only increased very little. The COD decreased with increasing ozone concentration. During the initial degradation period, the degradation rate was the highest at both low and high ozone concentrations. The degradation rate decreased with reaction time. The rate at a low ozone concentration decreased more significantly than at high ozone concentration. Although high ozone concentration is desirable for COD removal and degradation rate, the utilization efficiency of ozone decreased with increasing ozone concentration. The ozone utilization efficiency of the five-reactor device was three times higher than that of three tandem reactors, demonstrating that ozonation utilization efficiency can be improved by increasing the number of tandem reactors. Ozonation in tandem reactors is a promising approach for PML treatment.

Biological treatment of slaughterhouse wastewater: kinetic modeling and prediction of effluent

In this study three modeling approaches consisting Modified Stover-Kincannon, multilayer perceptron neural network (MLPANN) and B-Spline quasi interpolation were applied in order to predict effluent of up-flow anaerobic sludge blanket (UASB) reactor and also to find the reaction kinetics. At first run, the average total chemical oxygen demand (TCOD) removal efficiency was 48.3% with hydraulic retention time (HRT) of 26 h and 63.8% with HRT of 37 h, at OLR of 0.77-1.66 kg TCOD/m³ d. At the second run, UASB reactor operated with OLR of 1.94-3.1 kg TCOD/m³ d and achieved the average TCOD removal efficiency of 64.74 and 72.48% with HRT of 26 and 37 h, respectively. The Modified Stover-Kincannon performed well in terms of kinetic determination with a high value of regression coefficient over 0.98. The B-Spline quasi interpolation and MLPANN indicated a great fit for effluent prediction with average R of 0.9984 and 0.9986, and MSE of 157.6050 and 129.7796, respectively; however, they gave no information about reactions occurred in the system.

Electrochemical degradation of the antibiotic ciprofloxacin in a flow reactor using distinct BDD anodes: Reaction kinetics, identification and toxicity of the degradation products

The performances of distinct BDD anodes (boron doping of 100, 500 and 2500 ppm, with sp³/sp² carbon ratios of 215, 325, and 284, respectively) in the electrochemical degradation of ciprofloxacin - CIP (0.5 L of 50 mg L^-1 in 0.10 M Na₂SO₄, at 25 °C) were comparatively assessed using a recirculating flow system with a filter-press reactor. Performance was assessed by monitoring the CIP and total organic carbon (TOC) concentrations, oxidation intermediates, and antimicrobial activity against Escherichia coli as a function of electrolysis time. CIP removal was strongly affected by the solution pH (kept fixed), flow conditions, and current density; similar trends were obtained independently of the BDD anode used, but the BDD₁₀₀ anode yielded the best results. Enhanced mass transport was achieved at a low flow rate by promoting the solution turbulence within the reactor. The fastest complete CIP removal (within 20 min) was attained at j = 30 mA cm^-2, pH = 10.0, and q_V = 2.5 L min^-1 + bypass turbulence promotion. TOC removal was practically accomplished only after 10 h of electrolysis, with quite similar performances by the distinct BDD anodes. Five initial oxidation intermediates were identified (263 ≤ m/z ≤ 348), whereas only two terminal oxidation intermediates were detected (oxamic and formic acids). The antimicrobial activity of the electrolyzed CIP solution was almost completely removed within 10 h of electrolysis. The characteristics of the BDD anodes only had a marked effect on the CIP removal rate (best performance by the least-doped anode), contrasting with other data in the literature.

Heterotrophic Kinetic Study and Nitrogen Removal of a Membrane Bioreactor System Treating Real Urban Wastewater under a Pharmaceutical Compounds Shock: Effect of the Operative Variables

Numerous studies have analyzed the viability of the biodegradation and removal of different compounds of emerging concern in biological systems for wastewater treatment. However, the effect on the heterotrophic biomass of organic matter removal is sometimes missed. The aim of the present research was to study the effect of the addition of a mix of three pharmaceuticals (carbamazepine, ciprofloxacin, and ibuprofen) on the behavior of the biomass in two different membrane-based biological systems treating urban wastewater. The present research studied a membrane bioreactor (MBR) pilot plant operating at a similar mixed liquor suspended solids (MLSS) concentration (about 5.5 g/L). This system works as an MBR and is combined with a moving bed biofilm reactor (MBBR-MBR) to treat real urban wastewater at 6 and 10 h of hydraulic retention time (HRT) under three different shocks of pharmaceuticals with increasing concentrations. In all cases, the organic matter removal was, in average terms, higher than about 92% of biochemical oxygen demand on the fifth day (BOD5), 79% of chemical oxygen demand (COD), and 85% of total organic carbon (TOC). Nevertheless, the removal is higher in the MBBR-MBR technology under the same HRT and the MLSS is similar. Moreover, the removal increased during the shock of pharmaceutical compounds, especially in the MBR technology. From a kinetic perspective, MBBR-MBR is more suitable for low HRT (6 h) and MBR is more effective for high HRT (10 h). This could be due to the fact that biofilm systems are less sensitive to hostile environments than the MBR systems. The removal of N-NH4+ decreased considerably when the pharmaceutical compounds mix was introduced into the system until no removal was detected in cycle 1, even when biofilm was present.

Sonocatalytic degradation of butylparaben in aqueous phase over Pd/C nanoparticles

In the present work, the sonocatalytic degradation of butylparaben was investigated using Pd immobilized on carbon black as the sonocatalyst. The presence of 25 mg/L 10Pd/C significantly increased the removal rate of butylparaben and the observed kinetic constant increased from 0.0126 to 0.071 min^-1, while the synergy index between sonolysis and adsorption was 70.7%. The BP degradation followed pseudo-first-order kinetics with the apparent kinetic constant decreased from 0.071 to 0.030 min^-1 when the initial concentration of butylparaben increased from 0.5 to 2 mg/L. The process was being favored slightly under alkaline conditions. The presence of organic matter (20 mg/L humic acid) reduced the apparent kinetic constant more than two times. The addition of chlorides up to 250 mg/L did not significantly reduce the rate of reaction, while the presence of 250 mg/L bicarbonates reduced the observed kinetic constant from 0.071 to 0.0472 min^-1. The prepared catalyst retains the efficiency after five subsequent experiments since the apparent kinetic constant was only slightly decreased from 0.071 to 0.059 min^-1.

Development of hybrid processes for the removal of volatile organic compounds, plasticizer, and pharmaceutically active compound using sewage sludge, waste scrap tires, and wood chips as sorbents and microbial immobilization matrices

This study evaluated the reutilization of waste materials (scrap tires, sewage sludge, and wood chips) to remove volatile organic compounds (VOCs) benzene/toluene/ethylbenzene/xylenes/trichloroethylene/cis-1,2-dichloroethylene (BTEX/TCE/cis-DCE), plasticizer di(2-ethylhexyl) phthalate (DEHP), and pharmaceutically active compound carbamazepine from artificially contaminated water. Different hybrid removal processes were developed: (1) 300 mg/L BTEX + 20 mg/L TCE + 10 mg/L cis-DCE + tires + Pseudomonas sp.; (2) 250 mg/L toluene + sewage sludge biochar + Pseudomonas sp.; (3) 100 mg/L DEHP + tires + Acinetobacter sp.; and (4) 20 mg/L carbamazepine + wood chips + Phanerochaete chrysosporium. For the hybrid process (1), the removal of xylenes, TCE, and cis-DCE was enhanced, resulted from the contribution of both physical adsorption and biological immobilization removal. The hybrid process (2) was also superior for the removal of DEHP and required a shorter time (2 days) for the bioremoval. For the process (3), the biochar promoted the microbial immobilization on its surface and substantially enhanced/speed up the bioremoval of toluene. The fungal immobilization on wood chips in the hybrid process (4) also improved the carbamazepine removal considerably (removal efficiencies of 61.3 ± 0.6%) compared to the suspended system without wood chips (removal efficiencies of 34.4 ± 1.8%). These hybrid processes would not only be promising for the bioremediation of environmentally concerned contaminants but also reutilize waste materials as sorbents without any further treatment.

Cyclodextrin-enhanced 1,4-dioxane treatment kinetics with TCE and 1,1,1-TCA using aqueous ozone

Enhanced reactivity of aqueous ozone (O₃) with hydroxypropyl-β-cyclodextrin (HPβCD) and its impact on relative reactivity of O₃ with contaminants were evaluated herein. Oxidation kinetics of 1,4-dioxane, trichloroethylene (TCE), and 1,1,1-trichloroethane (TCA) using O₃ in single and multiple contaminant systems, with and without HPβCD, were quantified. 1,4-Dioxane decay rate constants for O₃ in the presence of HPβCD increased compared to those without HPβCD. Density functional theory molecular modeling confirmed that formation of ternary complexes with HPβCD, O₃, and contaminant increased reactivity by increasing reactant proximity and through additional reactivity within the HPβCD cavity. In the presence of chlorinated co-contaminants, the oxidation rate constant of 1,4-dioxane was enhanced. Use of HPβCD enabled O₃ reactivity within the HPβCD cavity and enhanced 1,4-dioxane treatment rates without inhibition in the presence of TCE, TCA, and radical scavengers including NaCl and bicarbonate. Micro-environmental chemistry within HPβCD inclusion cavities mediated contaminant oxidation reactions with increased reaction specificity.

Key structural features promoting radical driven degradation of emerging contaminants in water

Diverse contaminants of emerging concern (CECs) can be found in nowadays aquatic environment, possessing high potential to cause adverse ecological and human health effects. Due to their recalcitrance, conventional water treatment methods are shown to be inadequately effective. Thus, their upgrade by advanced oxidation processes, involving the generation of highly reactive species (HO and SO₄^-), is highly demanded. In order to assess the susceptibility of CECs by HO and SO₄^-, as well as to determine the corresponding reaction rate constants k_HO and k_SO4^-, the complex experimental studies has to be maintained. The alternative is the application of modeling approaches which correlate structural characteristics with activities/properties of interest, i.e. quantitative structure activity/property relationship (QSAR/QSPR). In this study k_HO and k_SO4^- of fifteen selected CECs were determined by competitive kinetics, and afterward used to elucidate key structural features promoting their degradation. In that purpose, QSPR models were constructed using multiple linear regression (MLR) combined with genetic algorithm (GA) approach. The models were submitted to the internal and external validation (using additional set of 17 CECs). Selected 3-variable models predicting k_HO and k_SO4^- were characterized with high accuracy and predictivity (R² = 0.876 and Q² = 0.847 and R² = 0.832 and Q² = 0.778, respectively). Although selected models at the first sight include descriptors derived through complicated calculation procedures, their weighting schemes indicate on their relevance and transparency toward established reaction theories and differences regarding radical type.

Solar reclamation of wastewater effluent polluted with bisphenols, phthalates and parabens by photocatalytic treatment with TiO2/Na2S2O8 at pilot plant scale

Investigations of anthropogenic contaminants in fresh- and wastewater have shown a wide variety of undesirable organic compounds such as Endocrine Disruptors (EDs). As a result, wastewater treatments using innovative technologies to remove those organic compounds are required. In this paper, the photodegradation of six EDs in wastewater at pilot plant scale is reported. The EDs were bisphenol A, bisphenol B, diamyl phthalate, butyl benzylphthalate, methylparaben and ethylparaben. Commercial TiO₂ nanopowders (P25, Alfa Aesar and Kronos vlp 7000) were used as photocatalysts. The operating variables (type and loading catalyst, effect of electron acceptor and pH) were previously optimized under laboratory conditions. The results show that the use of TiO₂ alongside an electron acceptor like Na₂S₂O₈ strongly enhances the degradation rate of the studied compounds compared with photolytic tests, especially P25. The oxidation rates of the EDs at pilot plant scale were calculated following the disappearance of the target compound as a function of fluence (H). The ED degradation followed a pseudo-first order kinetics in all cases. In our experimental conditions, the half-fluence (H₅₀) varied from 79 to 173 J cm^-2 (photolytic test), 10-117 J cm^-2 (TiO₂ vlp 7000) and 3-58 J cm^-2 (TiO₂ P25), for bisphenol B and butyl benzylphthalate, respectively. It is concluded that solar photocatalysis using the tandem TiO₂/Na₂S₂O₈ can be considered as an environmental-friendly tool for water detoxification and a sustainable technology for environmental remediation, especially in the Mediterranean Basin, where many places receive more than 3000 h of sunshine per year. Although the cost depends on the nature of the pollutant, the treatment cost was estimate to be about 150 € m^-3 for photocatalytic treatment with TiO₂ P25.

TiO2 Assisted Photodegradation for Low Substrate Concentrations and Transition Metal Electron Scavengers

Some contaminants of emerging concern (CECs) are known to survive conventional wastewater treatment, which introduces them back to the environment, allowing them to potentially cycle into drinking water. This is especially concerning because of the inherent ability of some CECs to induce physiological effects in humans at very low doses. Advanced oxidation processes (AOPs) such as TiO2-based photocatalysis are of great interest for addressing CECs in aqueous environments. Natural water resources often contain dissolved metal cation concentrations in excess of targeted CEC concentrations. These cations may significantly adversely impact the degradation of CECs by scavenging TiO2 surface generated electrons. Consequently, simple pseudo-first-order or Langmuir-Hinshelwood kinetics are not sufficient for reactor design and process analysis in some scenarios. Rhodamine Basic Violet 10 (Rhodamine B) dye and dissolved [Cu2+] cations were studied as reaction surrogates to demonstrate that TiO2-catalyzed degradation for very dilute solutions is almost entirely due to the homogeneous reaction with hydroxyl radicals, and that in this scenario, the hole trapping pathway has a negligible impact. Chemical reaction kinetic studies were then carried out to develop a robust model for RB-[Cu2+] reactions that is exact in the electron pathways for hydroxyl radical production and electron scavenging.

New Insights on the Photodegradation of Caffeine in the Presence of Bio-Based Substances-Magnetic Iron Oxide Hybrid Nanomaterials

The exploitation of organic waste as a source of bio-based substances to be used in environmental applications is gaining increasing interest. In the present research, compost-derived bio-based substances (BBS-Cs) were used to prepare hybrid magnetic nanoparticles (HMNPs) to be tested as an auxiliary in advanced oxidation processes. Hybrid magnetic nanoparticles can be indeed recovered at the end of the treatment and re-used in further water purification cycles. The research aimed to give new insights on the photodegradation of caffeine, chosen as marker of anthropogenic pollution in natural waters, and representative of the contaminants of emerging concern (CECs). Hybrid magnetic nanoparticles were synthetized starting from Fe(II) and Fe(III) salts and BBS-C aqueous solution, in alkali medium, via co-precipitation. Hybrid magnetic nanoparticles were characterized via X-ray diffraction (XRD), thermo-gravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy. The effect of pH, added hydrogen peroxide, and dissolved oxygen on caffeine photodegradation in the presence of HMNPs was assessed. The results allow for the hypothesis that caffeine abatement can be obtained in the presence of HMNPs and hydrogen peroxide through a heterogeneous photo-Fenton mechanism. The role of hydroxyl radicals in the process was assessed examining the effect of a selective hydroxyl radical scavenger on the caffeine degradation kinetic.

Optimization of process conditions for preparation of activated carbon from waste Salix psammophila and its adsorption behavior on fluoroquinolone antibiotics

Salix psammophila (SP), a solid waste abundantly available, was applied as a precursor to prepare the activated carbon by chemical activation method using phosphoric acid (H₃PO₄). Response surface methodology based on Box-Behnken design was used to optimize the prepared conditions of activated carbon. The effects of concentration of H₃PO₄, activation temperature and activation time on the adsorption performance (expressed by the adsorption capacity of ciprofloxacin hydrochloride (CIP) and norfloxacin (NOR)) were investigated. The optimum conditions were obtained using H₃PO₄ concentration of 67.83%, activation temperature of 567.44 °C and activation time of 86.61 min. The optimum activated carbon (SPAC) was characterized with scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), Brunauer-Emmett-Teller (BET) and Fourier transform infrared spectroscopy (FTIR). The adsorption behavior of CIP and NOR on SPAC was carried out and the mechanisms for the adsorption process were proposed. The equilibrium data were fitted by the Freundlich and Langmuir isotherm models, which resulted in 251.9 mg/g and 366.9 mg/g of the maximum monolayer adsorption for CIP and NOR at 25 °C, respectively. The best fitted kinetic model was pseudo-second-order, implying that chemisorption dominated in the adsorption process. This study indicated that activated carbon based on Salix psammophila (SPAC) was an excellent adsorbent for removing fluoroquinolone antibiotics from aqueous solutions.

Pharmaceutical products as emerging contaminant in water: relevance for developing nations and identification of critical compounds for Indian environment

Pharmaceuticals and personal care products (PPCPs) are contaminants of emerging concern and have been detected worldwide in water bodies in trace concentrations. Most of these emerging contaminants are not regulated in water quality standards except a few in the developed countries. In the case of developing countries, research in this direction is at a nascent stage. For the effective management of Pharmaceutical contaminants (PC) in developing countries, the relevance of PCs as an emerging contaminant has to be analyzed followed by regular monitoring of the environment. Considering the resource constraints, this could be accomplished by identifying the priority compounds which is again region specific and dependent on consumption behavior and pattern. In this work, relevance of pharmaceutical compound as emerging contaminant in water for a developing country like India is examined by considering the data pertaining to pharmaceutical consumption data. To identify the critical Pharmaceutical Contaminants to be monitored in the Indian environment, priority compounds from selected prioritization methods were screened with the compounds listed in National List of Essential Medicine (NLEM), India. Further, information on the number of publications on the compound as an emerging contaminant, data on monitoring studies in India and the number of brands marketing the compound in India were also analyzed. It is found that out of 195 compounds from different prioritization techniques, only 77 compounds were found relevant to India based on NLEM sorting.