Transformation of diazepam in water during UV/chlorine and simulated sunlight/chlorine advanced oxidation processes

Process analysis of microplastic aging during the photochemical oxidation process and its effect on the adsorption behavior of dissolved organic matter

Information on microplastics (MPs) interactions with dissolved organic matter (DOM) is essential for understanding their environmental impacts. However, research is scarce regarding the adsorption behavior of DOM with different characteristics onto pristine and aged MPs. This research thus investigates MPs aging behavior accelerated by UV/Persulfate and UV/chlorine oxidation processes and the adsorption behavior of organic matter with low-specific ultraviolet absorbance (L-SUVA) and high-SUVA (H-SUVA) characteristics. MPs were degraded by UV/Cl and UV/Persulfate for 30 days. Changes in thermal properties, surface morphology, and chemistry were studied using different analytical techniques. The adsorption behavior was assessed by adsorption kinetic and isotherm study. After oxidation, the surface of the MPs showed a significant increase in the oxygen-containing functional groups, contact angle, surface roughness, and surface energy, and a decrease in crystallinity. The oxidation effect follows the order of UV/Cl > UV/Persulfate. The kinetic and equilibrium data of H-SUVA adsorption on pristine and aged MPs well-fitted the pseudo-second-order and Langmuir model. In contrast, L-SUVA well-fitted the pseudo-first-order and Freundlich model. The adsorption capacity (qm) increased in the following orders: 8.11 > 5.87>4.29 mg g-1 for H-SUVA and 19.81 > 6.662>5.315 mg g-1 for L-SUVA by MPs aged with UV/Cl, UV/Persulfate and pristine MPs, respectively. The larger the surface damage of MPs, the greater the adsorption affinity of DOM. The result was attributed to the physical adsorption process, hydrophobic interactions, electrostatic, hydrogen, and halogen bonding. These findings are beneficial to provide new insights involving the adsorption behavior and interaction mechanisms of DOM onto MPs for the environmental risk assessment.

Effects of dissolved organic matter removal and molecular transformation in different water treatment processes on formation of disinfection byproducts

Alterations in molecular composition of dissolved organic matter (DOM) during water treatments can influence the composition and toxicity of disinfection by-products (DBPs) in subsequent chlorination disinfection process. In this study, the impacts of DOM composition after various water treatment techniques (coagulation, adsorption, nanofiltration, biological aerated filter (BAF), and their integrated processes) on the generation mechanisms of DBPs were comprehensively explored by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) in combination with GC-MS and LC-MS analysis. The results indicated that coagulation preferentially removed unsaturated (low H/C) and oxidized (high O/C) compounds, whereas adsorption was prone to remove the reduced (low O/C) component that was more reactive with chlorine, leading to lower yields (μg DBP/mg DOC) of trihalomethanes (THMs) and haloacetic acids (HAAs) during subsequent chlorination. The coagulation-adsorption technique exhibited a relatively high removal of both known and unknown DBPs, demonstrating that coagulation and adsorption were complementary for DOM removal at the molecular level. Nanofiltration selectively removed molecules with relatively high O/C, however, those with very low O/C that were more reactive with chlorine could pass through the nanofiltration membrane, resulting in the highest yields of THMs and HAAs. Although BAF was inefficient in removing DBPs precursors, it could convert molecules with low degree of oxidation and unsaturation into highly oxidized and unsaturated ones, thereby significantly enhancing the removal of DBPs precursors in the subsequent coagulation-adsorption process. These findings are instrumental in developing and selecting more effective techniques to minimize the formation of DBPs in water treatment.

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.

Evolution of reactive species and their contribution to the removal of ketamine and amine-containing pharmaceuticals during the sunlight/chlorine process

Sunlight-induced photoirradiation of chlorine (sunlight/chlorine) can be observed in outdoor swimming pools and open-channel disinfection units for wastewater treatment. In this study, the degradation of ketamine, an environmentally persistent pharmaceutical, under sunlight irradiation in the presence of a low concentration of chlorine (1 mg/L as Cl₂) was investigated to elucidate the evolution of reactive species and their contribution to ketamine removal. •OH dominates the initial stage of sunlight/chlorine; however, after chlorine depletion, reactions still progress with an observed rate constant (k_obs = 7.6 ± 0.50 × 10^-3 min^-1) an order of magnitude higher than photolysis alone (k_obs = 2.9 ± 0.15 × 10^-4 min^-1). When chlorine is depleted, O₃ becomes the major reactant that degrades ketamine. High O₃ yields were found in both sunlight/HOCl (12.5 ± 0.5% at pH 5) and sunlight/ClO^- (10 ± 1% at pH 10) systems. At sub-µM levels, O₃ resulted in substantial removal of ketamine, and even faster rates were observed in the presence of sunlight. A kinetic model was also established, and evaluate time-dependent concentration levels during sunlight/chlorine. The model simulation showed that the cumulative O₃ concentration could reach 0.91 μM, and O₃ contributed 31% ketamine removal during the sunlight/chlorine process. Primary and secondary amine functional groups were demonstrated to be the reaction sites of O₃; other pharmaceuticals, such as atenolol and metoprolol, underwent similar phenomena. In addition, the experimental and model results further indicated that sunlight/ClO₂^- or ClO₂ also participates in the degradation of ketamine with a minor role; trace amounts (below nM level) of ClO₂^- and ClO₂ were estimated by the simulation.

Determination and risk assessment of pharmaceutical residues in the urban water cycle in Selangor Darul Ehsan, Malaysia

The environmental fate of non-steroidal anti-inflammatory drugs (NSAIDs) in the urban water cycle is still uncertain and their status is mainly assessed based on specific water components and information on human risk assessments. This study (a) explores the environmental fate of NSAIDs (ibuprofen, IBU; naproxen, NAP; ketoprofen, KET; diazepam, DIA; and diclofenac, DIC) in the urban water cycle, including wastewater, river, and treated water via gas chromatography-mass spectrophotometry (GCMS), (b) assesses the efficiency of reducing the targeted NSAIDs in sewage treatment plant (STP) using analysis of variance (ANOVA), and (c) evaluates the ecological risk assessment of these drugs in the urban water cycle via teratogenic index (TI) and risk quotient (RQ). The primary receptor of contaminants comes from urban areas, as a high concentration of NSAIDs is detected (ranging from 5.87 × 10³ to 7.18 × 10⁴ ng/L). The percentage of NSAIDs removal in STP ranged from 25.6% to 92.3%. The NAP and KET were still detected at trace levels in treated water, indicating the persistent presence in the water cycle. The TI values for NAP and DIA (influent and effluent) were more than 1, showing a risk of a teratogenic effect. The IBU, KET, and DIC had values of less than 1, indicating the risk of lethal embryo effects. The NAP and DIA can be classified as Human Pregnancy Category C (2.1 > TI ≥ 0.76). This work proved that these drugs exist in the current urban water cycle, which could induce adverse effects on humans and the environment (RQ in high and low-risk categories). Therefore, they should be minimized, if not eliminated, from the primary sources of the pollutant (i.e., STPs). These pollutants should be considered a priority to be monitored, given focus to, and listed in the guideline due to their persistent presence in the urban water cycle.

Radical chemistry, degradation mechanism and toxicity evolution of BPA in the UV/chlorine and UV/H2O2

UV-assisted advanced oxidation processes (AOPs) are widely used and studied in degradation of bisphenol A (BPA). However, detailed information on their radical chemistry and degradation mechanisms is still lacking. In this study, degradation of BPA was comparatively evaluated to investigate the radical mechanisms, products and the toxicity variation in UV/chlorine and UV/H₂O₂ processes. In comparison with UV/H₂O₂, UV/chlorine had a higher BPA degradation efficiency and higher pH-dependency due to chlorination and the synergy of •OH and RCS. The •OH and Cl• played a pivotal role as the primary radicals in BPA degradation by UV/chlorine process at all pH investigated (6-8). The relative contributions of the secondary radicals ClO• gradually decreased with a variation of pH from 6 to 8 in this process. Presence of HCO₃^─ and HA inhibited BPA degradation to different extents in UV/chlorine process, while the effect of Cl^─ could be neglected. According to the identified transformation products, chlorination (major), hydroxylation and breakage of the isopropylidene chain were BPA decomposition pathways in the UV/chlorine system. In the UV/H₂O₂ system, only hydroxylation (major) and breakage of the isopropylidene chain occurred. The toxicity analysis, based on the proposed degradation pathways, indicated that the generation of chlorinated products in the UV/chlorine system led to a higher toxicity of the resulting mixture than in the UV/H₂O₂ system. Although UV/chlorine has an excellent BPA degradation effect and it is cost-effective, the possible environmental risk should be carefully considered when UV/chlorine system is used to remove BPA in real waters.

Performance and mechanism in degradation of typical antibiotics and antibiotic resistance genes by magnetic resin-mediated UV-Fenton process

Incomplete removal of antibiotics and antibiotic resistance genes (ARGs) has often been reported in wastewater treatment plants. More efficient treatment processes are needed to reduce their risks to the environment. Herein, we evaluated the degradation of antibiotics and ARGs by using magnetic anion exchange resin (MAER) as UV-Fenton catalyst. Sulfamethoxazole (SMZ), ofloxacin (OFX), and amoxicillin (AMX) were selected as the target compounds. The three antibiotics were almost completely degraded (> 99%) following the MAER UV-Fenton reaction for 30 min. From the degradation mechanism study, it was found that Fe³⁺/Fe²⁺ could be cyclically transferred from the catalyst at permeable interface, and the photo-generated electrons could be effectively separated. The dominant reactive radicals for antibiotics degradation were hydroxide during the MAER UV-Fenton reaction. The degradation pathway for sulfamethoxazole was proposed. In addition, wastewater samples from a wastewater treatment plant were applied to investigate the removal efficiency of antibiotics and their ARGs by the MAER UV-Fenton system. A rapid decrease in antibiotics and ARGs level was observed with this reaction system. The results from this study suggest that the MAER-mediated UV-Fenton reaction could be applied for the effective removal of antibiotics and ARGs in wastewater.

Toxicity reduction of persistent pollutants through the photo-fenton process and radiation/H2O2 using different sources of radiation and neutral pH

The presence of toxic compounds in aquatic bodies is of great concern, and the Fenton, photo-Fenton and radiation/H₂O₂ processes can be applied in the remediation of these compounds due to their efficiency and advantages. However, these processes need to be investigated to make them more viable and environmentally friendly. Thus, the reduction of toxicity was evaluated, through ecotoxicological tests with Artemia salina and Lactuca sativa, of the compounds 2,4-D, diazepam, nicotine and paracetamol (acetaminophen) by the Fenton, photo-Fenton and radiation/H₂O₂ process with UVC, UVA and natural solar radiation at neutral pH with low concentrations of Fe²⁺ and H₂O₂. The UVC/H₂O₂ process was efficient in the degradation of nicotine (74%), the photo-Fenton process was more efficient in the degradation of 2,4-D (82%), diazepam (27%) and paracetamol (85%) using solar radiation, UVA and UVC respectively. The toxicity and total organic carbon (TOC) tests showed a reduction in the toxicity of the compounds after treatment, except for diazepam, which was more resistant to the process, leading to a higher mortality of Artemia salinas (92%) and less relative seed germination of Lactuca sativa (40%).