Search Results (147)

This study investigates the formation and toxicity of disinfection by-products (DBPs) arising from the reactions between individual reactive chlorine species (RCS) and dissolved organic matter (DOM) during water treatment. Individual chlorine radicals (Cl^•) and dichloride radicals (Cl₂^•−) were selectively generated with a laser flash photolysis technique, and their interactions with Suwannee River natural organic matter (SRNOM) were analyzed. Results demonstrated a biphasic pattern of DBP formation, where initial increases in RCS exposure enhanced DBP concentrations and toxicities, followed by subsequent decreases at higher RCS exposure. Variations among DBP classes, including trichloromethanes, chloroacetic acids, and chloroacetaldehydes, highlighted the complexity of RCS-DOM interactions. Toxicity assessments further indicated chloroacetonitriles and chloroacetic acids as major toxicity contributors at varying RCS exposures. This study highlights the impact of RCS exposure levels to DBP formation and toxicities, providing mechanistic insights for optimizing parameters in RCS-mediated advanced oxidation processes (AOPs) for safer water treatment. Full article

Steroid hormones are micropollutants that contaminate water worldwide and have significant impacts on human health and the environment, even at very low concentrations. The aim of this article is to provide an overview of technologies for the removal of endocrine-disrupting compounds with a focus on oestrogens (estrone E1, 17β-oestradiol E2, estriol E3), the synthetic oestrogen (17α-ethinylestradiol EE2 and bisphenol A BPA), and pharmaceuticals found in wastewater. Hormonal and pharmaceutical contaminants are mostly persistent organic compounds that cannot be easily removed using conventional wastewater treatment processes. For this reason, researchers have tried to develop more efficient tertiary wastewater treatment technologies to reduce micropollutant concentrations in wastewater. This review covers the following processes: Advanced oxidation, nanofiltration, ultrasound, electro-Fenton processes, electrolysis, adsorption, ozonation, photolysis, photocatalysis, ultrafiltration, and electrocoagulation. Attention was paid to the effectiveness of the processes in terms of eliminating hormones and pharmaceuticals from wastewater, as well as on economic and environmental aspects. The combination of different processes can be a promising treatment scheme for retaining and degrading hormonal and pharmaceutical compounds from wastewater. With hybrid technologies, the advantages of the methods are combined to maximise the removal of pollutants. However, optimal methods of wastewater treatment depend on the quality and quantity of the wastewater, as well as the residual hormonal and pharmaceutical compounds and their hazardous effects. Full article

Industrial growth led to the expansion of existing environmental problems, where different kinds of pollutants can enter the environment by many known routes, particularly through wastewater. Among other contaminants, pharmaceuticals, such as diazepam, once released, pose a significant challenge related to their removal from complex environmental matrices due to their persistence and potential toxicity. For this reason, it is a great challenge to find suitable methods for the treatment of wastewater. The aim of this paper was to investigate the stability of diazepam, subjecting it to various degradation processes (hydrolysis and photolysis), focusing on photocatalysis, an advanced oxidation process commonly used for the purification of industrial wastewater. The photocatalytic system consisted of UV-A and simulated solar irradiation with titanium dioxide (TiO₂) immobilized on a glass mesh as a photocatalyst, with an additional reaction performed in the presence of an oxidizing agent, i.e., hydrogen peroxide, to improve diazepam removal from water matrices. The kinetic rate of diazepam degradation was monitored with a high-performance liquid chromatograph coupled with a photodiode array detector (HPLC-PDA). The target compound was characterized as a hydrolytically and photolytically stable compound with t_1/2 = 25 h. The presence of an immobilized TiO₂ catalyst contributed significantly to the degradation of diazepam under the influence of UV-A and simulated solar radiation, with t_1/2 in the range of 1.61–2.56 h. Five degradation products of diazepam were identified at the laboratory scale by MS analysis (m/z = 267, m/z = 273, m/z = 301, m/z = 271, and m/z = 303), while the toxicity assessment revealed that diazepam exhibited developmental toxicity and a low bioaccumulation factor. The pilot-scale process resulted in significant improvements in diazepam degradation with the fastest degradation kinetics (0.6888 h⁻¹). These results obtained at the pilot scale highlight the potential for industrial-scale implementation, offering a promising and innovative solution for pharmaceutical removal from wastewater. Full article

An aqueous mixture of three compounds (atrazine, carbamazepine, and p-chlorobenzoic acid) has been treated by photochemical processes including photolysis and photocatalysis with 10.7% TiO₂ supported on ceramic foams of mullite. Experiments were conducted in both ultrapure water and in a secondary effluent from a municipal wastewater treatment plant. Radiation at 365 nm was totally inefficient in the photolytic process carried out in ultrapure water; however, some sensitization phenomena were observed when municipal wastewater was used as a bulk matrix. In the latter case, conversion values in the range of 20–30% were obtained after 2 h. The photocatalytic process was much more effective experiencing conversions above 80% after just 80 min of reaction. The nature of the matrix used exerted a significant influence. Use of municipal wastewater slowed down the process due to the scavenging character of the natural organic matter content. Test runs in the presence of carbonates and t-butyl alcohol suggested that radical carbonates play some role in contaminant abatement, and secondary radicals generated after the t-BuOH attack by HO^● radicals should also be considered in the reaction mechanism. A pseudo-empirical mechanism of reactions sustains the experimental result obtained, acceptably modeling the effects of a water matrix, scavenger addition, and radiation volumetric photon flux. Full article

Nitro-functionalized heterocycles, such as nitroimidazoles, are significant environmental contaminants and have been identified as components of secondary organic aerosols (SOA) and biomass-burning organic aerosols (BBOA). Their strong absorption in the near-UV (300–400 nm) makes photochemistry a critical aspect of their atmospheric processing. This study investigates both the direct near-UV photochemistry and hydroxyl radical (OH) oxidation of 4-nitroimidazole (4-NI). The atmospheric photolysis rate of 4-NI in the near-UV (300–400 nm) was found to be J_4-NI = 4.3 × 10⁻⁵ (±0.8) s⁻¹, corresponding to an atmospheric lifetime of 391 (±77) min under bulk aqueous conditions simulating aqueous aerosols and cloud water. Electrospray ionization mass spectrometry (ESI-MS) analysis following irradiation indicated loss of the nitro group, while NO elimination was observed as a more minor channel in direct photolysis. In addition, the rate constant for the reaction of 4-NI with OH radicals, k_NI+OH, was determined to be 2.9 × 10⁹ (±0.6) M⁻¹s⁻¹. Following OH oxidation, ESI-MS results show the emergence of a dominant peak at m/z = 130 amu, consistent with hydroxylation of 4-NI. Computational results indicate that OH radical addition occurs with the lowest barrier at the C2 and C5 positions of 4-NI. The combined results from direct photolysis and OH oxidation experiments suggest that OH-mediated degradation is likely to dominate under aerosol-phase conditions, where OH radical concentrations are elevated, while direct photolysis is expected to be the primary loss mechanism in high-humidity environments and bulk cloud water. Full article

Antimicrobial fragrances, commonly found in household and personal care products, are frequently detected in water bodies, yet their environmental fate and transformation mechanisms remain inadequately explored. This study investigates the photochemical transformation of cinnamaldehyde (CA), a representative antimicrobial fragrance, and its consequence for toxicological effects. The results showed that under UV irradiation, 94.6% CA was eliminated within 60 min, with a degradation rate of 0.059 min⁻¹. Laser flash photolysis, quenching experiments, and electron paramagnetic resonance spectra identified O₂^•− and ³CA^* as the important species, contributing 29.4% and 33.6%, respectively, to the transformation process. Additionally, singlet oxygen (¹O₂), hydroxyl radicals (^•OH), and solvated electrons (e_aq⁻) were involved in mediating the oxidation reactions. These species facilitated photoionization and oxidation, resulting in the formation of five major transformation products, including cis-cinnamyl aldehyde, cinnamic acid, styrene, 1aH-indeno [1,2-b]oxirene), and 1-Oxo-1H-indene. Most of these products were persistent, and exhibited considerable ecotoxicological risks. Specifically, the cinnamic acid and 1-Oxo-1H-indene caused severe skin irritation, while cinnamic acid induced significant eye irritation. Notably, the transformation products demonstrated sensitizing effects on human skin. This study underscores the overlooked ecotoxicological risks associated with the photochemical transformation of antimicrobial fragrances, revealing their potential to generate potent allergens and other harmful byproducts. Full article

Pharmaceutical residues are emerging contaminants of growing concern due to their persistence and poor removal efficiency in conventional wastewater treatment plants. This study evaluates UVC photolysis with type C ultraviolet radiation (UVC) and UVC/TiO₂ photocatalysis of a mixture of four pharmaceuticals—atenolol (ATL), acetaminophen (ACM), clofibric acid (CLA), and antipyrine (ANT)—commonly found in treated urban wastewater. A comprehensive kinetic model was developed to describe their degradation, taking into account the generation of reactive oxygen species (ROS): hydroxyl (HO^●), superoxide ion (O₂^●−) radicals, and singlet oxygen (¹O₂), along with their reactions with both the pharmaceuticals and dissolved organic matter. Direct quantum yields were determined as 8.05 × 10⁻³ mol·Einstein⁻¹ for ATL, 1.93 × 10⁻³ for ACM, 3.12 × 10⁻¹ for CLA, and 5.12 × 10⁻² for ANT. In addition, rate constants of the reactions between singlet oxygen and pharmaceuticals were 9.93, 1.3 × 10⁶, 1.18 × 10², and 1.14 × 10⁴ M⁻¹s⁻¹ for ATL, ACM, CLA, and ANT, respectively. Scavenger experiments confirmed the key role of the ROS involved. The model reproduces the inhibitory effect of natural organic matter in secondary effluent and, in most cases, treated, accurately predicts the concentration profiles of the pharmaceuticals. Under photocatalytic conditions (0.10 g·L⁻¹ TiO₂), all compounds were completely degraded in less than 15 min. This validated model provides a useful tool for understanding the degradation mechanisms of pharmaceutical mixtures and for supporting the design of effective water strategies based on photochemical processes. Full article

The extensive use of antibiotics as essential medications in contemporary healthcare has resulted in significant amounts of these drugs entering the environment, both in original and metabolic forms, which presents serious ecological and health hazards. This paper examines the natural processes that break down antibiotics in water, including photolysis, hydrolysis, and biodegradation. It also discusses advancements in artificial degradation technologies, such as advanced oxidation processes (AOPs), physicochemical methods, ionizing radiation degradation, artificial wetland technology, microalgae technology, microbial electrochemical systems, and innovative catalysts. While current technologies demonstrate promising potential for use, they encounter challenges related to the catalyst stability, cost, and ecological safety. Future research should focus on optimizing degradation methods and creating efficient, sustainable multi-technology systems, such as the photocatalysis–membrane filtration coupling system; the ultrasound–Fenton–artificial wetland synergistic system; the electrochemical–biodegradation combined system; and the microbial fuel cell (MFC)–photocatalysis synergistic system, to tackle the complexities of antibiotic pollution in the environment. Full article

This experiment investigated the degradation of amoxicillin in water using hydrogen peroxide (H₂O₂) and UV Irradiation. The parameters analyzed included the initial concentration of amoxicillin, the pH of the solution, and the quantity of H₂O₂ used. These factors were examined to assess the effectiveness of the photodegradation process. No degradation of amoxicillin was observed in the dark during stirring for 20 min. The investigation demonstrated successful photodegradation of amoxicillin using H₂O₂ as an oxidant in the presence of UV Irradiation. The pH of the irradiated solution significantly influenced the degradation of amoxicillin, with minimal degradation at acidic pH and a gradual increase as the pH shifted towards more basic conditions. Degradation was more pronounced with higher concentrations of H₂O₂, while it decreased as the concentration of amoxicillin in the reacting solution increased. Complete degradation was achieved using 3 mL of H₂O₂. The experimental data were well-fitted to zero-order reaction kinetics. The findings of this investigation show significant improvements compared to previously reported results in the field of photocatalysis using nanomaterials and photolysis techniques involving UV and H₂O₂. The novelty of our research is in the different experimental parameters used for the UV/H₂O₂ photolysis process, which distinguishes it from other previous investigations. The UV/H₂O₂ system proved highly effective in the photodegradation of amoxicillin, making it a viable option for degrading other organic pollutants commonly found in industrial wastewater. Full article

Sulfonamides, including sulfadoxine (SDX), are widely used antibiotics, particularly for malaria treatment. However, their extensive use has led to environmental pollution, microbial resistance, and public health risks. Advanced Oxidation Processes (AOPs) offer promising methods to degrade such pollutants in water, though they may generate more toxic by-products. This study evaluates three AOPs with different hydroxyl radical generation principles: the Fenton reagent (H₂O₂/Fe²⁺), hydrogen peroxide photolysis (UV-C/H₂O₂), and heterogeneous photocatalysis (UV-A/TiO₂). Heterogeneous photocatalysis showed superior performance, achieving 100% degradation and 77% mineralization under optimized conditions. Further analysis explored the effects of UV dose, catalyst concentration, and pH on process efficiency. The influence of water matrices, including Ultrapure Water (UW), Tap Water (TW), and Surface Water (SW) from the Aliakmonas River, was also examined. High-Resolution Mass Spectrometry identified 11 SDX transformation products formed during photocatalysis, with their formation mechanisms reported for the first time. An ecotoxicity assessment using ECOSAR software revealed insights into the potential environmental impact of these by-products. Full article

The photolysis kinetics of propaquizafop in water under ultraviolet light was investigated in this study, and the effects of different influencing factors (pH, ${\mathrm{N}\mathrm{O}}_3^{-}$, metal ions) on the photolysis of propaquizafop were clarified. Propaquizafop residues in water were determined by a HPLC-UV detector. The results showed that the pH of the aqueous solution had no significant effect on the photolysis of propaquizafop (p < 0.05). The low ${\mathrm{N}\mathrm{O}}_3^{-}$, concentration (0.5~2 mmol/L) had a weak inhibitory effect on the photolysis of the propaquizafop; when the concentration of ${\mathrm{N}\mathrm{O}}_3^{-}$ was 4 mmol/L, the degradation half-life of the propaquizafop was significantly higher than with other treatments (p < 0.05); Different concentrations of Fe³⁺ had varying degrees of inhibitory effects on the photolysis of propaquizafop. The inhibitory effect was stronger at low concentrations (0.5 mmol/L and 1 mmol/L) and weaker at high concentrations (2 mmol/L and 4 mmol/L). As the concentrations of Cu²⁺, Cd²⁺, Mn²⁺, Zn²⁺, and Ni²⁺ increased, their inhibitory effect on the photolysis of propaquizafop in an aqueous solution became stronger. In addition, LC–QTOF-MS was used to identify the photoproducts of propaquizafop in aqueous solution in this study. Five types of photoproducts were identified, and several propaquizafop degradation pathways and mechanisms were proposed, mainly including rearrangement, cracking reactions, dechlorination reactions, and light-induced redox reactions. The results of this study will help us to better understand the photodegradation law of propaquizafop in aqueous solution and provide data support for its safety evaluation in water. Full article

Suspended particulate matter (SPM) is an important component of natural water bodies and can significantly influence the photolytic behavior of water pollutants. A comprehensive understanding of the photochemical behavior of water pollutants in natural waters requires consideration of the presence of SPM. In this study, montmorillonite–humic acid (MMT-HA) composite particles were synthesized to simulate SPM in natural waters and their effects on the photolysis of tetracycline (TC) were investigated. The results demonstrated that the presence of MMT-HA composite particles in water significantly enhanced the photolysis of TC, with the photolytic kinetics following a pseudo-first-order model. Electron spin resonance spectra and free radical quenching experiments indicated that the photoactive components (MMT and humic acids) in the composite particles induced the generation of reactive oxygen species under light exposure, further contributing to the enhanced photolysis of TC. Comparative analysis of the free radical signals and adsorption experiments revealed that the accelerated photolysis of TC was also related to the interfacial interaction between the MMT in the composite particles and the TC molecules. The formation of surface complexes between TC molecules and the negatively charged sites on the MMT surface facilitated light absorption and electron transfer, thereby accelerating the photolysis of TC. Photoproduct analysis indicated that the primary degradation pathways of TC in the composite particle systems included the addition of hydroxyl radicals to the aromatic ring, as well as demethylation, deamination and dehydration in the side chains. This study shows that SPM in water bodies can affect the photochemical behavior of pollutants and should be taken into account when assessing the phototransformation of pollutants in natural waters. Full article

Amoxicillin (AMX) is utilized in the treatment of several infectious diseases, and its concentration in wastewater has increased quite significantly over the years, posing high health hazards for humans and other living organisms. Investigations are in progress globally to eliminate AMX and other related pollutants using several methods that include adsorption, photolysis, photocatalytic degradation, photoelectrocatalytic degradation, and electrochemical conversion. AMX can be eliminated efficiently from the environment using photodegradation, either by photolysis or a photocatalytic process. Several types of semiconductor NMs have been used to eliminate AMX and other related drugs present in wastewater. This review spans the photodegradation studies conducted during the years 2018–2024 to degrade and eliminate AMX in aquatic systems. Several studies have been reported to eliminate AMX from different water streams. These studies are categorized into TiO₂-containing and non-TiO₂-based catalysts for better comparison. A section on photolysis is also included, showing the use of UV alone or with H₂O₂ or PS without using any nanomaterial. A tabulated summary of both types of catalysts showing the catalysts, reaction conditions, and degradation efficiency is presented. Researchers have used a variety of reaction conditions that include radiation types (UV, solar, and visible), pH of the solution, concentration of AMX, number of nanomaterials, presence of other additives and activators such as H₂O₂ as oxidant, and the influence of different salts like NaCl and CaCl₂ on the photodegradation efficiency. TiO₂ was the best nanomaterial found that achieved the highest degradation of AMX in ultraviolet irradiation. TiO₂ doped with other nanomaterials showed very good performance under visible light. WO₃ was also used by several investigators and found quite effective for AMX degradation. Other metal oxides used for AMX elimination were derived from molybdenum, zinc, manganese, copper, cerium, silver, etc. Some researchers have used UV and/or visible irradiation or sunlight, without using solid catalysts, in the presence of oxidants such as H₂O₂. A summarized description of earlier published reviews is also presented. Full article

Clear and sanitarily adequate water scarcity is one of the greatest problems of modern society. Continuous population growth, rising organics concentrations, and common non-efficient wastewater treatment technologies add to the seriousness of this issue. The employment of various advanced oxidation processes (AOPs) in water treatment is becoming more widespread. In this review, the state-of-the-art application of three AOPs is discussed in detail: photocatalysis, sonophotolysis, and sonophotocatalysis. Photocatalysis utilizes semiconductor photocatalysts to degrade organic pollutants under light irradiation. Sonophotolysis combines ultrasound and photolysis to generate reactive radicals, enhancing the degradation of organic pollutants. Sonophotocatalysis synergistically combines ultrasound with photocatalysis, resulting in improved degradation efficiency compared to individual processes. By studying this paper, readers will get an insight into the latest published data regarding the above-mentioned processes from the last 10 years. Different factors are compared and discussed, such as degradation efficiency, reaction kinetics, catalyst type, ultrasound frequency, or water matrix effects on process performance. In addition, the economic aspects of sonophotolysis, photocatalysis, and sonophotocatalysis will be also analyzed and compared to other processes. Also, the future research directions and potential applications of these AOPs in wastewater treatment will be highlighted. This review offers invaluable insights into the selection and optimization of AOPs. Full article

The photodegradation of azithromycin present was carried out in water using H₂O₂ under UV irradiation. The reaction variables considered in this study were the amount of H₂O₂ solution and the initial concentration of azithromycin to evaluate the performance of the photodegradation process. The azithromycin degradation was not observed in the dark during stirring for 20 min. The study showed an efficient photodegradation of azithromycin using H₂O₂ as an oxidant in the presence of UV irradiation. The azithromycin degradation was altered significantly by the pH of the irradiated solution. The degradation was low at an acidic pH and showed an increasing trend as the pH changed to basic. The azithromycin degradation increased with a higher amount (higher concentration) of H₂O₂. The degradation of azithromycin decreased with a higher concentration of azithromycin in the reacting solution. The highest degradation of AZT was achieved in 1 h using a 1.0 ppm AZT solution containing 3 mL of H₂O₂. The experimental data obtained were well-fitted to zero-order reaction kinetics. The results of this study were found quite excellent. They showed 100% degradation in 1 h when compared with those reported in the literature, both with photocatalysis using nanomaterials and photolysis using light irradiation and/or H₂O₂. The UV/H₂O₂ system was found to be quite efficient for the photodegradation of azithromycin, and this system can be applied to degrade other organic pollutants present in industrial wastewater. Full article