Kinetic study of colored species formation during paracetamol removal from water in a semicontinuous ozonation contactor

Redox-directed identification of toxic transformation products during ozonation of aromatics

The toxicity assessment of transformation products (TPs) formed in oxidative water treatment is crucial but challenging because of their low concentration, structural diversity, and mixture complexity. Here, this study developed a novel redox-directed approach for identification of toxic TPs without the individual toxicity and concentration information. This approach based on sodium borohydride reduction comprised an integrated process of toxicological evaluation, fluorescence excitation-emission matrix characterization, high-resolution mass spectrometry detection, followed by ecological toxicity assessment of identified TPs. The redox-directed identification of primary causative toxicants was experimentally tested for the increased nonspecific toxicity observations in the ozonated effluents of model aromatics. Reduction reaction caused a remarkable decrease in toxicity and increase in fluorescence intensity, obtaining a good linear relation between them. More than ten monomeric or dimeric p-benzoquinone (p-BQ) TPs were identified in the ozonated effluents. The occurrence of the p-BQ TPs was further verified through parallel sodium sulfite reduction and actual wastewater ozonation experiments. In vitro bioassays of luminescent bacteria, as well as in silico genotoxicity and cytotoxicity predictions, indicate that the toxicity of p-BQ TPs is significantly higher than that of their precursors and other TPs. These together demonstrated that the identified p-BQ TPs are primary toxicity contributors. The redox-directed approach facilitated the revelation of primary toxicity contribution, illustrating emerging p-BQs are a concern for aquatic ecosystem safety in the oxidative treatment of aromatics-contaminated wastewater.

Enzymatic post-treatment of ozonation: laccase-mediated removal of the by-products of acetaminophen ozonation

Ozonation is a powerful technique to remove micropollutants from wastewater. As chemical oxidation of wastewater comes with the formation of varying, possibly persistent and toxic by-products, post-treatment of the ozonated effluent is routinely suggested. This study explored an enzymatic treatment of ozonation products using the laccase from Trametes versicolor. A high-performance liquid chromatography coupled with high-resolution mass spectrometry (HPLC-HRMS) analysis revealed that the major by-products were effectively degraded by the enzymatic post-treatment. The enzymatic removal of the by-products reduced the ecotoxicity of the ozonation effluent, as monitored by the inhibition of Aliivibrio fischeri. The ecotoxicity was more effectively reduced by enzymatic post-oxidation at pH 7 than at the activity maximum of the laccase at pH 5. A mechanistic HPLC-HRMS and UV/Vis spectroscopic analysis revealed that acidic conditions favored rapid conversion of the phenolic by-products to dead-end products in the absence of nucleophiles. In contrast, the polymerization to harmless insoluble polymers was favored at neutral conditions. Hence, coupling ozonation with laccase-catalyzed post-oxidation at neutral conditions, which are present in wastewater effluents, is suggested as a new resource-efficient method to remove persistent micropollutants while excluding the emission of potentially harmful by-products.

A critical review over the removal of paracetamol (acetaminophen) from synthetic waters and real wastewaters by direct, hybrid catalytic, and sequential ozonation processes

Paracetamol (PCT) or acetaminophen is a widely prescribed drug to treat fever and mild to moderate pain. The PCT uptake by animals and humans is not complete, being excreted through their urine to contaminate the aquatic/natural environments. Trace amounts of this drug have been found in sewage sludge, hospital wastewaters, wastewater plant treatments, surface waters, and even drinking water. PCT denatures proteins and oxidize lipids in cells with damage of their genetic code. Its toxicity over macrophytes, protozoan, algae, bacteria, and fishes has been reported. Ozonation methods have been proposed as efficient treatments to solve this pollution. This comprehensive and critical review is focused on the application of ozonation processes to remove PCT polluted water from different sources, like natural waters, synthetic waters, and real wastewaters. The fundamentals, operating variables, and best results by direct ozonation and hybrid catalytic ozonation are described, with attention to produced reactive oxygen species and their oxidative action. Single ozonation, catalytic modification of materials, and hybrid non-catalytic processes are detailed as direct ozonation methods. Ozonation with metal-based catalysts and photolytic and photocatalytic ozonation as hybrid catalytic methods are analyzed. Sequential non-biological and biological treatments with ozone and ozonation for wastewater remediation in treatment plants are described. Reaction sequences proposed for PCT mineralization are finally discussed, showing the initial formation of hydroquinone and 2-hydroxy-4-(N-acetyl)-aminophenol and their consecutive evolution to ultimate carboxylic acids like oxalic and oxamic. The ability of the methods to destroy these acids and their iron- and/or copper-complexes explains their mineralization performance.

Changes in solution turbidity and color during paracetamol removal in laboratory and pilot-scale semicontinuous ozonation reactors

Injecting ozone by means of a venturi device causes an increase in the mass transfer coefficient with respect to gas dissolution through a microdiffuser. Moreover, it was observed that significant turbidity levels are not formed (<1 NTU) when using a microdiffuser, probably due to the relatively high stirring which avoids formation of intermolecular hydrogen bonds. On the contrary, employing a venturi injector led to the production of high turbidity levels in water (up to 20 NTU). This indicates that formation of supramolecular structures causing this turbidity requires the presence of certain facilitating species which are formed through ozone decomposition mechanisms. The maximum ozone transfer takes place when operating at pH0 9.0, that is, when this value is close to the pKa and employing a dose of R = 115 mol O3/mol Pa0. Under these conditions, the degradation of paracetamol generates color, which is attributed to the presence of condensation products from pyrogallol, catechol, resorcinol, acetamide, oxalic acid and 4-aminophenol. Once paracetamol is fully degraded and solution turns colorless, turbidity grows (>20 NTU). This is attributed to formation of high molecular weight structures from 4-aminophenol and oxamide. Operating with large ozone excess (R = 500 mol O3/mol Pa0), the maximum ozone transfer rate is achieved at pH0 = 12.0. Under these conditions, the pollutant is fully removed together with water aromaticity and oxalic acid (able to form linear structures through hydrogen bonding) is detected during color development. Then, turbidity is formed due to cyclic dimer formation from acetic acid.

Sustainable Mitigation of Paracetamol with a Novel Dual-Functionalized Pullulan/Kaolin Hydrogel Nanocomposite from Simulated Wastewater

In the present investigation, a novel, green, and economical dual-functionalized pullulan/kaolin hydrogel nanocomposite (f-PKHN) was fabricated and subsequently applied for the liquid-phase decontamination of paracetamol (PCT), a pharmaceutical pollutant. Pullulan and kaolin were functionalized with l-asparagine and gallic acid, respectively. The physicochemical facets of the functionalized pullulan/kaolin hydrogel nanocomposite and its interactive behavior with PCT were elucidated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX), and elemental mapping. The process parameters along with the isotherm, kinetics, and thermodynamics were methodically appraised via a batch technique to unveil the adsorption performance of the as-fabricated hydrogel nanocomposite. The adsorption isotherm and kinetics of PCT uptake by f-PKHN conform well to Freundlich and pseudo-second-order models, respectively. Relying on hydrogen bonding, n-π, and van der Waals interactions, the maximum adsorption capacity was 332.54 mg g^-1, higher than for most of the previous adsorbents reported in the literature for PCT removal. Thermodynamic calculations corroborated endothermic, spontaneous, and feasible adsorption phenomena. The maintenance of a high uptake percentage (69.11%) in the fifth consecutive adsorption-desorption cycle implied the significant reusable potential of f-PKHN. Swelling studies exhibited 90% swelling within 200 min, indicating the successful fabrication of a cross-linked hydrogel network. The real water (distilled water, tap water, and river water) samples spiked with PCT specified a significant uptake of PCT (>85%), and the minor influence of ionic strength on the adsorptive potential of f-PKHN validated its potentiality for the decontamination of real effluents. In conclusion, f-PKHN with substantial adsorption capacity, green characteristics, and excellent reusability can be reckoned with as a promising adsorbent for the de-escalation of PCT from aquatic sources as well as at the industrial level.

Ozone Kinetic Studies Assessment for the PPCPs Abatement: Mixtures Relevance

The increasing consumption of pharmaceutical and personal care products (PPCPs) by humankind has been causing an accumulation of contaminants (commonly referred to as contaminants of emerging concern), in effluents and water resources. Ozonation can be used to improve the removal of these contaminants during water treatment to alleviate this burden. In this work, the degradation of methyl (MP), propylparaben (PP), paracetamol (PCT), sulfamethoxazole (SMX), and carbamazepine (CBZ) by ozonation was assessed both for individual compounds and for mixtures with increasing complexity (two to five compounds). Ozonation was performed at pH3 to gain an insight on the exclusive action of molecular ozone as oxidizing agent. The degradation of contaminants was described as a function of time and transferred ozone dose, and the corresponding pseudo-first order kinetic rate constants (k’) were determined. PPCPs were degraded individually within 1.5 to 10 min. CBZ was the most quickly degraded (k’ = 1.25 min−1) and MP the most resistant to ozone (k’ = 0.25 min−1). When in the mixture, the degradation rate of the contaminants was slower. For parabens, the increase of the number of compounds in the mixture led to an exponential decrease of the k’ values. Moreover, the presence of more PPCPs within the mixture increased energy consumption associated with the treatment, thereby reflecting higher economic costs.

Minute Cu2+ coupling with HCO3- for efficient degradation of acetaminophen via H2O2 activation

Homogeneous Cu²⁺-mediated activation of H₂O₂ has been widely applied for the removal of organic contaminants, but fairly high dosage of Cu²⁺ is generally required and may cause secondary pollution. In the present study, minute Cu²⁺ (2.5 μM) catalyzed H₂O₂ exhibited excellent efficiency in degradation of organic pollutants with the assistant of naturally occurring level HCO₃^- (1 mM). In a typical case, acetaminophen (ACE) was completely eliminated within 10 min which followed the pseudo-first-order kinetics. Singlet oxygen and superoxide radical rather than traditionally identified hydroxyl radical were the predominant reactive oxygen species (ROS) responsible for ACE degradation. Meanwhile, Cu³⁺ was deduced through Cu⁺ and p-hydroxybenzoic acid formation analysis. CuCO₃(aq) was the main complex with high reactivity for the activation of H₂O₂ to form ROS and Cu³⁺. The removal efficiency of ACE depended on the operating parameters, such as Cu²⁺, HCO₃^- and H₂O₂ dosage, solution initial pH. The presence of Cl^-, HPO₄^2-, humic acid were found to retard ACE removal while other anions such as SO₄^2- and NO₃^- had no obvious effect. ACE exhibited lower degradation efficiency in real water matrices than that in ultra-pure water. Nevertheless, 58-100% of ACE was removed from domestic wastewater, lake water and tap water within 60 min. Moreover, eight intermediate products were identified and the possible degradation pathways of ACE were proposed. Additionally, other typical organic pollutants including bisphenol A, norfloxacin, lomefloxacin hydrochloride and sulfadiazine, exhibited great removal efficiency in the Cu²⁺/H₂O₂/HCO₃^- system.

Turbidity Changes during Carbamazepine Oxidation by Photo-Fenton

The objective of this study is to evaluate the turbidity generated during the Fenton photo-reaction applied to the oxidation of waters containing carbamazepine as a function of factors such as pH, H2O2 concentration and catalyst dosage. The results let establish the degradation pathways and the main decomposition byproducts. It is found that the pH affects the turbidity of the water. Working between pH = 2.0 and 2.5, the turbidity is under 1 NTU due to the fact that iron, added as a catalyst, is in the form of a ferrous ion. Operating at pH values above 3.0, the iron species in their oxidized state (mainly ferric hydroxide in suspension) would cause turbidity. The contribution of these ferric species is a function of the concentration of iron added to the process, verifying that the turbidity increases linearly according to a ratio of 0.616 NTU L/mg Fe. Performing with oxidant concentrations at (H2O2) = 2.0 mM, the turbidity undergoes a strong increase until reaching values around 98 NTU in the steady state. High turbidity levels can be originated by the formation of coordination complexes, consisting of the union of three molecules containing substituted carboxylic groups (BaQD), which act as ligands towards an iron atom with Fe3+ oxidation state.

Changes of dissolved oxygen in aqueous solutions of caffeine oxidized by photo-Fenton reagent

ABSTRACT Formation of oxygen in the caffeine aqueous solutions occurs through self-decomposition reactions of the hydrogen peroxide, used as an oxidant in the photo-Fenton treatment. The total concentration of hydrogen peroxide used in the treatment would be the contribution of the stoichiometric concentration that reacts with the organic matter ([H₂O₂]₀= 2.0 mM) and the excess of oxidant that decomposes to oxygen, through radical mechanisms, according to a ratio of 0.8164 mmol H₂O₂ mg^-1 O₂. When operating at concentrations lower than [H₂O₂]₀= 2.0 mM, oxygen is not released because there is no excess of oxidant. Moreover, it is verified that the ferrous ion catalyst is oxidized to ferric ion and its subsequent regeneration to ferrous ion. Working at concentrations higher than [H₂O₂]₀= 2.0 mM, oxygen is released in the water, verifying that the catalyst remains as ferric species, which does not regenerate. The reaction time in which oxygen evolution happpens depends on the concentration of catalyst used in the oxidation, verifying that the highest oxygen generation rates are obtained when applying [Fe]₀= 10.0 mg L^-1. Once generated in the water, the maximum concentration of oxygen begins to decrease as the hydrogen peroxide is consumed, until reaching a constant value. The stages of formation and decrease of oxygen are adjusted to zero-order kinetics, estimating the kinetics constants as a function of the catalyst concentration: k _f= 29.48 [Fe]₀ ^-1.25 (mg O₂ L^-1 min^-1) and k _d= -0.006 [Fe]₀ ^2.0 + 0.244 [Fe]₀-3.69 (mg O₂ L^-1 min^-1).

Heterogeneous Catalytic Ozonation of Aniline-Contaminated Waters: A Three-Phase Modelling Approach Using TiO2/GAC

This work aims to study the sustainable catalytic ozonation of aniline promoted by granular active carbon (GAC) doped with TiO2. Aniline was selected as a model compound for the accelerator manufacturing industries used in the manufacture of rubber due to its environmental impact, low biodegradability, and harmful genotoxic effects on human health. Based on the evolution of total organic carbon (TOC), aniline concentration measured using high performance liquid chromatography (HPLC), pH and ozone concentration in liquid and gas phase, and catalyst loading, a three-phase reaction system has been modelled. The proposed three-phase model related the ozone transfer parameters and the pseudo-first order kinetic constants through three coefficients that involve the adsorption process, oxidation in the liquid, and the solid catalyst. The interpretation of the kinetic constants of the process allowed the predominance of the mechanism of Langmuir–Hinshelwood or modified Eley–Rideal to be elucidated. Seven intermediate aromatic reaction products, representative of the direct action of ozone and the radical pathway, were identified and quantified, as well as precursors of the appearance of turbidity, with which two possible routes of degradation of aniline being proposed.

Innovative spherical biochar for pharmaceutical removal from water: Insight into adsorption mechanism

In this study, we developed an innovative spherical biochar with high porosity and excellent paracetamol (PRC) adsorption capacity. The optimal pyrolysis temperatures for the preparation of spherical biochar (derived from pure glucose) and non-spherical biochar (from pomelo peel wastes) were obtained at 900 °C and 700 °C, respectively. Various advanced techniques were applied to characterize the prepared biochars. Spherical and non-spherical biochars exhibited large specific surface area (1292 and 1033 m²/g) and high total pore volume (0.704 and 1.074 cm³/g), respectively. The adsorption behavior of PRC onto two biochars was conducted utilizing batch experiments. Results demonstrated that the adsorption process was slightly affected by the change of solution pH (2-11) and addition of NaCl (0.05-1.0 M) and was able to achieve fast equilibrium (∼120 min). The maximum adsorption capacity of spherical biochar (286 mg/g) for PRC was approximately double that of non-spherical biochar (147 mg/g). The signal of thermodynamic parameters was negative ΔG° and ΔH° values, but positive ΔS° value. The adsorption mechanism consisted of pore-filling, hydrogen bonding formations, n-π and π-π interactions, and van der Waals force. The adsorption capacities of two biochars were insignificantly dependent on different real water samples containing PRC. Consequently, the biochars can serve as a green and promising material for efficiently removing PRC from water.

Electrochemical oxidation of acetaminophen and its transformation products in surface water: effect of pH and current density

Several studies have been conducted worldwide to develop effective and affordable methods to degrade pharmaceuticals and their metabolites/intermediates/oxidation products found in surface water, wastewater and drinking water. In this work, acetaminophen and its transformation products were successfully degraded in surface water by electrochemical oxidation using stainless steel electrodes. The effect of pH and current density on the oxidation process was assessed and the oxidation kinetics and mechanisms involved were described. Additionally, the results were compared with those obtained in acetaminophen synthetic solutions. It was found that conducting the electrochemical oxidation at 16.3 mA/cm² and pH 5, good performance of the process was achieved and not only acetaminophen, but also its transformation products were totally degraded in only 7.5 min; furthermore, small number of transformation products were generated. On the other hand, degradation rates of acetaminophen and its transformation products in surface water were much faster (more than 2.5 times) and the reaction times much shorter (more than 4.0 times) than in synthetic solutions at all current densities and pH values evaluated. At pH 3 and pH 5, greater soluble chlorine formation due to the higher HCl amount used to acidify the surface water solutions could enhance the degradation rates of acetaminophen and its transformation products. However, constituents of surface water (ions and solids) could also have an important role on the oxidation process because at pH 9 (non-acidified solutions) the degradation rates were also much greater and the reaction times were much shorter in surface water than in acetaminophen synthetic solutions.

Integration of catalytic ozonation and adsorption processes for increased efficiency of textile wastewater treatment

Advanced and optimized textile wastewater treatment by catalytic ozonation and activated carbon (AC) adsorption was investigated. Scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy indicated that Mn and Ce oxides were successfully loaded on the γ-Al₂ O₃ support, and MnO₂ , Mn₂ O₃ , CeO₂ , and Ce₂ O₃ were the main components of the catalyst. Actual textile wastewater from biochemical effluent was used as experiment wastewater. The removal efficiencies of chemical oxygen demand (COD) and chromaticity were approximately 30.6% (414-287 mg/L on average) and 99.3% (4,033 times to 27 times on average), respectively during the 30-day on-site continuous-flow test with an ozone dosage, contact time, and gas-liquid ratio of 100 mg/L, 15.7 min, and 2.9, respectively. Following 1 g/L AC adsorption, the effluent COD concentration was reduced to 40 mg/L. By contrast, AC adsorption without catalytic ozonation as pretreatment required 10 g/L AC dosage to achieve similar treatment results. Gas chromatography-mass spectrometry analyses indicated that volatile phenols, sulfides, and aniline in wastewater were completely removed after treatment. Inductively coupled plasma results further showed that the active components of MnO_x -CeO_x in the catalyst were stable after continuous use for 60 days. PRACTITIONER POINTS: Mesoporous catalyst synthesized by impregnating MnO_x -CeO_x on γ-Al₂ O₃ support. Catalytic ozonation and AC adsorption were combined to degrade organics. Maximum degradation of COD and chromaticity by optimizing process variables. The efficiency of the method was compared to that of single AC adsorption.