Ozonation of carbamazepine and its main transformation products: product determination and reaction mechanisms

Limitations of wastewater treatment plants in removing trace anthropogenic biomarkers and future directions: A review

This review highlights the limitations faced by conventional wastewater treatment plants (WWTPs) in effectively removing contaminants of emerging concern (CECs), heavy metals (HMs), and Escherichia coli (E. coli). This emphasises the limitations of current treatment methods and advocates for innovative approaches to enhance the removal efficiency. By following the PRISMA guidelines, the study systematically reviewed relevant literature on detecting and remedying these pollutants in wastewater treatment facilities. Conventional wastewater treatment plants struggle to eliminate CECs, HMs, and E. coli owing to their small size, persistence, and complex nature. The review suggests upgrading WWTPs with advanced tertiary processes to significantly improve contaminant removal. This calls for cost-effective treatment parameters and standardised assessment techniques to enhance the fate of MPs in WWTPs and WRRFs. It recommends integrating insights from mass-balance model studies on MPs in WWTP to overcome modelling challenges and ensure model reliability. In conclusion, this review underscores the urgent need for advancements in wastewater treatment processes to mitigate the environmental impact of trace anthropogenic biomarkers. Future efforts should focus on conducting comprehensive studies, implementing advanced treatment methods, and optimising management practices in WWTPs and WRRFs.

A critical review on the pathways of carbamazepine transformation products in oxidative wastewater treatment processes

Carbamazepine (CBZ) is an anticonvulsant drug, released in domestic and hospital wastewater, and one of the drugs most commonly detected in surface water. Conventional secondary processes do a very poor job of removing it (<25 %), but its concentrations are significantly reduced by polishing oxidation processes. However, there are still many unknowns regarding the transformation products generated and their fate. This review first presents the journey of CBZ and its transformation products (TPs) in wastewater, from human consumption to discharge in water bodies. It then goes on to detail the diversity of mechanisms responsible for CBZ degradation and the generation of multiple TPs, laying the emphasis on the different types of advanced oxidation processes (AOP). 135 TPs were reported and a map describing their formation/degradation pathways was drawn up. This work highlights the wide range of physicochemical properties and toxicity effects of TPs on aquatic organisms and provides information about TPs of interest for future research. Finally, this review concludes on the importance of quantifying TPs and of determining kinetic characteristics to produce more accurate reaction schemes and computer-based fate predictions.

Guidance document on the impact of water treatment processes on residues of active substances or their metabolites in water abstracted for the production of drinking water

This guidance document provides a tiered framework for risk assessors and facilitates risk managers in making decisions concerning the approval of active substances (AS) that are chemicals in plant protection products (PPPs) and biocidal products, and authorisation of the products. Based on the approaches presented in this document, a conclusion can be drawn on the impact of water treatment processes on residues of the AS or its metabolites in surface water and/or groundwater abstracted for the production of drinking water, i.e. the formation of transformation products (TPs). This guidance enables the identification of actual public health concerns from exposure to harmful compounds generated during the processing of water for the production of drinking water, and it focuses on water treatment methods commonly used in the European Union (EU). The tiered framework determines whether residues from PPP use or residues from biocidal product use can be present in water at water abstraction locations. Approaches, including experimental methods, are described that can be used to assess whether harmful TPs may form during water treatment and, if so, how to assess the impact of exposure to these water treatment TPs (tTPs) and other residues including environmental TPs (eTPs) on human and domesticated animal health through the consumption of TPs via drinking water. The types of studies or information that would be required are described while avoiding vertebrate testing as much as possible. The framework integrates the use of weight-of-evidence and, when possible alternative (new approach) methods to avoid as far as possible the need for additional testing.

Environmental concerns and bioaccumulation of psychiatric drugs in water bodies - Conventional versus biocatalytic systems of mitigation

The COVID-19 pandemic has brought increments in market sales and prescription of medicines commonly used to treat mental health disorders, such as depression, anxiety, stress, and related problems. The increasing use of these drugs, named psychiatric drugs, has led to their persistence in aquatic systems (bioaccumulation), since they are recalcitrant to conventional physical and chemical treatments typically used in wastewater treatment plants. An emerging environmental concern caused by the bioaccumulation of psychiatric drugs has been attributed to the potential ecological and toxicological risk that these medicines might have over human health, animals, and plants. Thus, by the application of biocatalysis-assisted techniques, it is possible to efficiently remove psychiatric drugs from water. Biocatalysis, is a widely employed and highly efficient process implemented in the biotransformation of a wide range of contaminants, since it has important differences in terms of catalytic behavior, compared to common treatment techniques, including photodegradation, Fenton, and thermal treatments, among others. Moreover, it is noticed the importance to monitor transformation products of degradation and biodegradation, since according to the applied removal technique, different toxic transformation products have been reported to appear after the application of physical and chemical procedures. In addition, this work deals with the discussion of differences existing between high- and low-income countries, according to their environmental regulations regarding waste management policies, especially waste of the drug industry.

Ozonation of carbamazepine in the presence of sulfur-dopped graphene: Effect of process parameters and formation of main transformation products

The stability of graphene structure in sulfur-doped graphene catalyst is demonstrated to be a key aspect during the ozonation process. Enhancing the stability of the sulfur-doped graphene structure is therefore important to improve its catalytic activity during the ozonation process. However, this has remained a challenge so far. Therefore, we adopted a low-energy microwave plasma technique to synthesize a high purity sulfur-doped graphene (S ⎯ Gr) catalyst for the ozonation process. The effect of S ⎯ Gr in the ozonation process was tested using carbamazepine (CBZ; 0.05 mM) as a probe compound. A complete CBZ removal was obtained at an ozone concentration of 0.08 mM while in comparison with single O₃, ∼1.5 and 2.5 times decrease in the formation of the two important intermediate transformation products i.e., BQM (1-(2-benzaldehyde) - 4-hydroxy (1H, 3H)-quinazoline-2-one) and BQD (1-(2-benzaldehyde) - (1H, 3H)-quinazoline-2, 4-dione) was observed. Radical scavenging experiments confirmed the formation of HO. The XPS results showed that the activity of S ⎯ Gr towards the formation of HO was positively related to S-bearing carbon atoms at the edge of the graphene structure. Therefore, the addition of S ⎯ Gr is directly linked with the formation of HO, which further contributed to the improved elimination of intermediate transformation products. With a low sulfur loss of 1 %, the microwave plasma synthesized S ⎯ Gr catalyst remained stable during ozonation, implying its feasibility in practical application.

Ozone Diffusion through a Hollow Fiber Membrane Contactor for Pharmaceuticals Removal and Bromate Minimization

Recently, ozonation has been advocated as a solution to tackle emerging contaminants. Hollow fiber membrane contactors (HFMC) have a lower residual ozone concentration than bubble reactors that could limit the formation of potential ozonation by-products, especially bromates that are regulated in drinking water. The aim of this study was to evaluate ozonation with HFMC for pharmaceutical abatement and bromate minimization compared to bubble columns in wastewater. A HFMC, composed of 65 polytetrafluoroethylene hollow fibers with a 0.45 mm/0.87 mm inner/external diameter and a 0.107 m² exchange surface, was used for the ozonation of real-treated wastewater spiked with 2 µM of p-chlorobenzoic acid (p-CBA) and 3 mg.L^-1 of bromide. p-CBA was tracked to monitor the production of strongly-oxidant hydroxyl radicals from the decomposition of the molecular ozone. At 100% p-CBA abatement, 1600 µg.L^-1 of bromate was formed with the HFMC, whereas 3486 µg.L^-1 was formed with the bubble column. These results demonstrate that HFMC can produce a significant amount of hydroxyl radicals while limiting bromate formation in real-treated wastewater. The test water was also spiked with carbamazepine and sulfamethoxazole to evaluate the abatement efficiency of the process. Short contact times (approximately 2s) achieved high rates of pharmaceuticals removal without bromate formation.

Full-Scale O3/Micro-Nano Bubbles System Based Advanced Oxidation as Alternative Tertiary Treatment in WWTP Effluents

Wastewater treatment plant effluents can be an important source of contamination in agricultural reuse practices, as pharmaceuticals are poorly degraded by conventional treatments and can enter crops, thereby becoming a toxicological risk. Therefore, advanced tertiary treatments are required. Ozone (O3) is a promising alternative due to its capacity to degrade pharmaceutical compounds, together with its disinfecting power. However, mass transfer from the gas to the liquid phase can be a limiting step. A novel alternative for increased ozone efficiency is the combination of micro-nano bubbles (MNBs). However, this is still a fairly unknown method, and there are also many uncertainties regarding their implementation in large-scale systems. In this work, a combined O3/MNBs full-scale system was installed in a WWTP to evaluate the removal efficiency of 12 pharmaceuticals, including COVID-19-related compounds. The results clearly showed that the use of MNBs had a significantly positive contribution to the effects of ozone, reducing energy costs with respect to conventional O3 processes. Workflow and ozone production were key factors for optimizing the system, with the highest efficiencies achieved at 2000 L/h and 15.9 gO3/h, resulting in high agronomic water quality effluents. A first estimation of the transformation products generated was described, jointly with the energy costs required.

Ozonation of 14C-labeled micropollutants - mineralization of labeled moieties and adsorption of transformation products to activated carbon

Ozonation transformation products (OTPs) are largely unknown compounds that are formed during the ozonation of micropollutants, and it is uncertain to which extent these compounds can be removed by subsequent adsorption to activated carbon. Thus, ¹⁴C-labeled micropollutants were ozonated to generate ¹⁴C-labeled OTPs, for which the adsorption of the sum of all ¹⁴C-labeled OTPs to activated carbon could be determined, based on the adsorption of the labeled carbon. Further, ¹⁴CO₂ traps were used to examine the mineralization of ¹⁴C-labeled moieties during ozonation. ¹⁴CO₂-formation revealed a partial mineralization of the ¹⁴C-labeled moieties in all compounds except for propyl-labeled bisphenol A and O-methyl-labeled naproxen. A similar degree of mineralization was noted for different compounds labeled at the same moiety, including the carboxylic carbon in diclofenac and ibuprofen (∼40% at 1 g O₃/g DOC) and the aniline ring in sulfamethoxazole and sulfadiazine (∼30% at 1 g O₃/g DOC). Aromatic ring cleavage was also confirmed for bisphenol A, sulfamethoxazole, and sulfadiazine through the formation of ¹⁴CO₂. The adsorption experiments demonstrated increased adsorption of micropollutants to powdered activated carbon after ozonation, which was connected to a decreased adsorption of dissolved organic matter (DOM). Conversely, the OTPs showed a substantial and successive decline in adsorption at increased ozone doses for all compounds, likely due to decreased hydrophobicity and aromaticity of the OTPs. These findings indicate that adsorption to activated carbon alone is not a viable removal method for a wide range of ozonation transformation products.

Ecotoxicological Consequences of the Abatement of Contaminants of Emerging Concern by Ozonation—Does Mixture Complexity Matter?

Ozonation has been used to degrade persistent water contaminants, namely, pharmaceuticals and personal care products (PPCPs). However, ozonation can lead to by-products that can be more toxic than the parent compounds. This work aims to assess whether the ecotoxicological effects of ozonation are modified as the initial matrix being treated increases in complexity, considering mixtures of 2, 3, 4 and 5 PPCPs. The following PPCPs were used: two parabens (metylparaben (MP) and propylparaben (PP)), paracetamol (PCT), sulfamethoxazole (SMX) and carbamazepine (CBZ). The following model species were used to assess toxicity: the crustacean Daphnia magna, the microalgae Raphidocelis subcapitata, the macrophyte Lemna minor and the watercress Lepidium sativum. There was a trend of increased toxicity with increasing mixture complexity of the untreated samples, except for D. magna. The same was observed after ozonation with the exception of the mixture MP+PP, which showed high toxicity to all the tested species, namely 100% immobilization of D. magna. The toxicity of SMX to the primary producers decreased pronouncedly after ozonation, except for L. minor. This study highlights the importance of considering the complexity of the matrix being treated and of using an ecotoxicological test battery with a wide diversity of species for assessing ozonation efficiency.

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.

Oxidation of 51 micropollutants during drinking water ozonation: Formation of transformation products and their fate during biological post-filtration

Micropollutants (MP) with varying ozone-reactive moieties were spiked to lake water in the influent of a drinking water pilot plant consisting of an ozonation followed by a biological sand filtration. During ozonation, 227 transformation products (OTPs) from 39 of the spiked 51 MPs were detected after solid phase extraction by liquid chromatography high-resolution mass spectrometry (LC-HRMS/MS). Based on the MS/MS data, tentative molecular structures are proposed. Reaction mechanisms for the formation of a large number of OTPs are suggested by combination of the kinetics of formation and abatement and state-of-the-art knowledge on ozone and hydroxyl radical chemistry. OTPs forming as primary or higher generation products from the oxidation of MPs could be differentiated. However, some expected products from the reactions of ozone with activated aromatic compounds and olefins were not detected with the applied analytical procedure. 187 OTPs were present in the sand filtration in sufficiently high concentrations to elucidate their fate in this treatment step. 35 of these OTPs (19%) were abated in the sand filtration step, most likely due to biodegradation. Only 24 (13%) of the OTPs were abated more efficiently than the parent compounds, with a dependency on the functional group of the parent MPs and OTPs. Overall, this study provides evidence, that the common assumption that OTPs are easily abated in biological post-treatment is not generally valid. Nevertheless, it is unknown how the OTPs, which escaped detection, would have behaved in the biological post-treatment.

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.