Attenuation of pharmaceutically active compounds in aqueous solution by UV/CaO2 process: Influencing factors, degradation mechanism and pathways

A review on the antibiotic florfenicol: Occurrence, environmental fate, effects, and health risks

Florfenicol, as a replacement for chloramphenicol, can tightly bind to the A site of the 23S rRNA in the 50S subunit of the 70S ribosome, thereby inhibiting protein synthesis and bacterial proliferation. Due to the widespread use in aquaculture and veterinary medicine, florfenicol has been detected in the aquatic environment worldwide. Concerns over the effects and health risks of florfenicol on target and non-target organisms have been raised in recent years. Although the ecotoxicity of florfenicol has been widely reported in different species, no attempt has been made to review the current research progress of florfenicol toxicity, hormesis, and its health risks posed to biota. In this study, a comprehensive literature review was conducted to summarize the effects of florfenicol on various organisms including bacteria, algae, invertebrates, fishes, birds, and mammals. The generation of antibiotic resistant bacteria and spread antibiotic resistant genes, closely associated with hormesis, are pressing environmental health issues stemming from overuse or misuse of antibiotics including florfenicol. Exposure to florfenicol at μg/L-mg/L induced hormetic effects in several algal species, and chromoplasts might serve as a target for florfenicol-induced effects; however, the underlying molecular mechanisms are completely lacking. Exposure to high levels (mg/L) of florfenicol modified the xenobiotic metabolism, antioxidant systems, and energy metabolism, resulting in hepatotoxicity, renal toxicity, immunotoxicity, developmental toxicity, reproductive toxicity, obesogenic effects, and hormesis in different animal species. Mitochondria and the associated energy metabolism are suggested to be the primary targets for florfenicol toxicity in animals, albeit further in-depth investigations are warranted for revealing the long-term effects (e.g., whole-life-cycle impacts, multigenerational effects) of florfenicol, especially at environmental levels, and the underlying mechanisms. This will facilitate the evaluation of potential hormetic effects and construction of adverse outcome pathways for environmental risk assessment and regulation of florfenicol.

Effects of wavelength on the treatment of contaminants of emerging concern by UV-assisted homogeneous advanced oxidation/reduction processes

Pollutants of emerging concern in aqueous environments present a significant threat to both the aquatic ecosystem and human health due to their rapid transfer. Among the various treatment approaches to remove those pollutants, UV-assisted advanced oxidation/reduction processes are considered competent and cost-effective. The treatment effectiveness is highly dependent on the wavelength of the UV irradiation used. This article systematically discusses the wavelength dependency of direct photolysis, UV/peroxides, UV/chlor(am)ine, UV/ClO2, UV/natural organic matter, UV/nitrate, and UV/sulfite on the transformation of contaminants. Altering wavelengths affects the photolysis of target pollutants, photo-decay of the oxidant/reductant, and quantum yields of reactive species generated in the processes, which significantly impact the degradation rates and formation of disinfection byproducts. In general, the degradation of contaminants is most efficient when using wavelengths that closely match the highest molar absorption coefficients of the target pollutants or the oxidizing/reducing agents, and the contribution of pollutant absorption is generally more significant. By matching the wavelength with the peak absorbance of target compounds and oxidants/reductants, researchers and engineers have the potential to optimize the UV wavelengths used in UV-AO/RPs to effectively remove pollutants and control the formation of disinfection byproducts.

Eco-friendly oxidation of a reactive textile dye by CaO2: effects of specific independent parameters

Textile wastewater containing dyes poses significant risks to the environment. Advanced oxidation processes (AOPs) effectively eliminate dyes by converting them into harmless substances. However, AOPs have drawbacks such as sludge formation, metal toxicity, and high cost. As an alternative to AOPs, calcium peroxide (CaO2) offers an eco-friendly and potent oxidant for dye removal. Unlike certain AOPs that generate sludge, CaO2 can be directly employed without resulting in sludge formation. This study examines the use of CaO2 for oxidizing Reactive Black 5 (RB5) in textile wastewater without any activator. Various independent factors-pH, CaO2 dosage, temperature, and certain anions-were investigated for their influence on the oxidation process. The effects of these factors on dye oxidation were analyzed using the Multiple Linear Regression Method (MLR). CaO2 dosage was determined to be the most influential parameter for RB5 oxidation, while the optimal pH for oxidation with CaO2 was found to be 10. The study determined that 0.5 g of CaO2 achieved approximately 99% efficiency in oxidizing 100 mg/L of RB5. Additionally, the study revealed that the oxidation process is endothermic, with an activation energy (Ea) and standard enthalpy (ΔH°) for RB5 oxidation by CaO2 determined as 31.135 kJ mol-1 and 110.4 kJ mol-1, respectively. The presence of anions decreased RB5 oxidation, with decreasing effectiveness observed in the order of PO43-, SO42-, HCO3-, Cl-, CO32-, and NO3-. Overall, this research highlights CaO2 as an effective, easy-to-use, eco-friendly, and cost-efficient method for removing RB5 from textile wastewater.

Degradation of tetracyclines via calcium peroxide activation by ultrasonic: Roles of reactive species, oxidation mechanism and toxicity evaluation

Tetracyclines (TC) frequently detected in the aqueous environment pose threats to humans and ecosystems. The synergistic technology coupling ultrasound (US) and calcium peroxide (CaO₂) has a great potential to abate TC in wastewater. However, the degradation efficiency and detailed mechanism of TC removal in the US/CaO₂ system is unclear. This work was carried out to assess the performance and mechanism of TC removal in the US/CaO₂ system. The results demonstrated that 99.2% of TC was degraded by the combination of 15 mM CaO₂ with ultrasonic power of 400 W (20 kHz), but only about 30% and 4.5% of TC was removed by CaO₂ (15 mM) or US (400 W) alone process, respectively. Experiments using specific quenchers and electron paramagnetic resonance (EPR) analysis indicated that the generation of hydroxyl radicals (•OH), superoxide radicals (O₂^-•), and single oxygen (¹O₂) in the process, whereas •OH and ¹O₂ were mainly responsible for the degradation of TC. The removal of TC in the US/CaO₂ system has a close relationship with the ultrasonic power, the dosage of CaO₂ and TC, and the initial pH. The degradation pathway of TC in the US/CaO₂ process was proposed based on the detected oxidation products, and it mainly included N,N-dedimethylation, hydroxylation, and ring-opening reactions. The presence of 10 mM common inorganic anions including chloridion (Cl^-), nitrate ion (NO₃^-), sulfate ion (SO₄^2-), and bicarbonate ion (HCO₃^-) showed negligible influences on the removal of TC in the US/CaO₂ system. The US/CaO₂ process could efficiently remove TC in real wastewater. Overall, this work firstly demonstrated that •OH and ¹O₂ mainly contributed to the removal of pollutants in the US/CaO₂ system, which was remarkable for understanding the mechanisms of CaO₂-based oxidation process and its future application.

Sunlight-mediated CaO2 inactivation of pathogen indicator organisms in surface water system: Roles of reactive species, characterization of pathogen inactivation

In the era of the current epidemic, it is urgent to control pathogens in sewage, eliminate the source of infection, and optimize the technology for killing pathogens. Combining calcium peroxide (CaO₂) with sunlight is considered a potentially efficient, economical, and eco-friendly method for pathogen-contaminated water remediation. This paper evaluated the solar activating properties of CaO₂ for inactivating pathogenic indicators and explored the roles of reactive species contributing to pathogen inactivation. Moreover, these reactive species' average steady-state concentrations and second-order reaction rate were tentatively explored, and mechanistic model for photoinactivation were establishment. Pathogen's inactivation was mainly attributed to direct photoinactivation (13∼50%) and exogenous indirect mechanisms with corresponding contributions of reactive species, i.e., OH^- (14∼23%), ¹O₂ (12∼28%), •OH (20∼32%), O₂^•- (12∼16%), and H₂O₂ (6∼11%). Furthermore, cell membrane rupture and DNA damage were observed by transmission electron microscopy (TEM) and agarose gel electrophoresis (AGE) experiments. Among experiments on common aqueous constituents influencing photoinactivation, copper and iron ions were found to promote a pathogen-inactivating ability of the system, while fulvic acids (FA) and humic acid (HA) had the opposite effect. This study revealed the potential of CaO₂/sunlight to inactivate pathogens and laid a foundation for its application in inactivating pathogens in surface water.

Removal of chloramphenicol antibiotics in natural and engineered water systems: Review of reaction mechanisms and product toxicity

Chloramphenicol antibiotics are widely applied in human and veterinary medicine. They experience natural attenuation and/or chemical degradation during oxidative water treatment. However, the environmental risks posed by the transformation products of such organic contaminants remain largely unknown from the literature. As such, this review aims to summarize and analyze the elimination efficiency, reaction mechanisms, and resulting product risks of three typical chloramphenicol antibiotics (chloramphenicol, thiamphenicol, and florfenicol) from these transformation processes. The obtained results suggest that limited attenuation of these micropollutants is observed during hydrolysis, biodegradation, and photolysis. Comparatively, prominent abatement of these compounds is accomplished using advanced oxidation processes; however, efficient mineralization is still difficult given the formation of recalcitrant products. The in silico prediction on the multi-endpoint toxicity and biodegradability of different products is systematically performed. Most of the transformation products are estimated with acute and chronic aquatic toxicity, genotoxicity, and developmental toxicity. Furthermore, the overall reaction mechanisms of these contaminants induced by multiple oxidizing species are revealed. Overall, this review unveils the non-overlooked and serious secondary risks and biodegradability recalcitrance of the degradation products of chloramphenicol antibiotics using a combined experimental and theoretical method. Strategic improvements of current treatment technologies are strongly recommended for complete water decontamination.

In-situ chemical attenuation of pharmaceutically active compounds using CaO2: Influencing factors, mechanistic modeling, and cooperative inactivation of water-borne microbial pathogens

Water polluted by pharmaceutically active compounds (PhACs) and water-borne pathogens urgently need to develop eco-friendly and advanced water treatment techniques. This paper evaluates the potential of using calcium peroxide (CaO₂), a safe and biocompatible oxidant both PhACs (thiamphenicol, florfenicol, carbamazepine, phenobarbital, and primidone) and pathogens (Escherichia coli, Staphylococcus aureus) in water. This paper evaluates the potential of using calcium peroxide (CaO₂) as a safe and biocompatible oxidant to remove both PhACs (thiamphenicol, florfenicol, carbamazepine, phenobarbital, and primidone) and pathogens (Escherichia coli, Staphylococcus aureus) in water. The increased CaO₂ dosage increased efficiencies of PhACs attenuation and pathogens inactivation, and both exhibited pseudo-first-order degradation kinetics (R² > 0.90). PhACs attenuation were mainly via oxidization (H₂O₂, •OH/O^•-, and O₂^•-) and alkaline hydrolysis (OH^-) from CaO₂. Moreover, concentrations of these reactive species and their contributions to PhACs attenuation were quantified, and mechanistic model was established and validated. Besides, possible transformation pathways of target PhACs except primidone were proposed. As for pathogen indicators, the suitable inactivation dosage of CaO₂ was 0.1 g L^-1. The oxidability (18-64%) and alkalinity (82-36%) generated from CaO₂ played vital roles in pathogen inactivation. In addition, CaO₂ at 0.01-0.1 g L^-1 can be applied in remediation of SW contaminated by PhACs and pathogenic bacteria, which can degrade target PhACs with efficiencies of 21-100% under 0.01 g L^-1 CaO₂, and inactivate 100% of test bacteria under 0.1 g L^-1 CaO₂. In short, capability of CaO₂ to remove target PhACs and microbial pathogens reveals its potential to be used as a representative technology for the advanced treatment of waters contaminated by organic compounds and microbial pathogens.

Motivation of reactive oxygen and nitrogen species by a novel non-thermal plasma coupled with calcium peroxide system for synergistic removal of sulfamethoxazole in waste activated sludge

Large amounts of antibiotics are concentrated in waste activated sludge (WAS) and released into the environment. It is thus critical to develop advanced sludge treatment technology to remove these antibiotics. Dielectric barrier discharge (DBD) combined with calcium peroxide (CaO₂), as an innovative technology to attenuate sulfamethoxazole (SMX) in sludge, was investigated. Evident synergistic effects between DBD and CaO₂ were observed on the SMX degradation with a synergistic factor of 2.02. Moreover, the energy consumption of DBD/CaO₂ was significantly lower than that of DBD alone. At a typical CaO₂ dosage of 0.1 g/g TS and discharge power of 64.5 W, the highest SMX removal of 96% was achieved within 50 min. The synergistic effects of DBD/CaO₂ could be associated with the base catalysis of H₂O₂ and O₃, UV-base-photolysis, peroxone oxidation, and photocatalytic H₂O₂. DBD/CaO₂ generated various reactive oxygen species (ROS) and nitrogen species (RNS) that participated in SMX removal. The contributions of these reactive species followed the sequence of e^- > •OH > •O₂^- > ¹O₂ > ONOO^-. Based on the detected transformation by-products and their variations during treatment, a plausible SMX degradation pathway in sludge was proposed. Besides, DBD/CaO₂ also promoted sludge disintegration, dewatering, heavy metal removal, sludge reduction, sludge solubilization, and acetate-enriched volatile fatty acid (VFA) production. Therefore, DBD/CaO₂ exhibited great potential for controlling antibiotic, as well as promoting sludge reduction, decontamination, and resourcization.

A comprehensive review on the use of algal-bacterial systems for wastewater treatment with emphasis on nutrient and micropollutant removal

The scarcity of water resources and environmental pollution have highlighted the need for sustainable wastewater treatment. Existing conventional treatment systems are energy-intensive and not always able to meet stringent disposal standards. Recently, algal-bacterial systems have emerged as environmentally friendly sustainable processes for wastewater treatment and resource recovery. The algal-bacterial systems work on the principle of the symbiotic relationship between algae and bacteria. This paper comprehensively discusses the most recent studies on algal-bacterial systems for wastewater treatment, factors affecting the treatment, and aspects of resource recovery from the biomass. The algal-bacterial interaction includes cell-to-cell communication, substrate exchange, and horizontal gene transfer. The quorum sensing (QS) molecules and their effects on algal-bacterial interactions are briefly discussed. The effect of the factors such as pH, temperature, C/N/P ratio, light intensity, and external aeration on the algal-bacterial systems have been discussed. An overview of the modeling aspects of algal-bacterial systems has been provided. The algal-bacterial systems have the potential for removing micropollutants because of the diverse possible interactions between algae-bacteria. The removal mechanisms of micropollutants - sorption, biodegradation, and photodegradation, have been reviewed. The harvesting methods and resource recovery aspects have been presented. The major challenges associated with algal-bacterial systems for real scale implementation and future perspectives have been discussed. Integrating wastewater treatment with the algal biorefinery concept reduces the overall waste component in a wastewater treatment system by converting the biomass into a useful product, resulting in a sustainable system that contributes to the circular bioeconomy.

New insights into thiamphenicol biodegradation mechanism by Sphingomonas sp. CL5.1 deciphered through metabolic and proteomic analysis

Biological treatment is an efficient and economical process to remove thiamphenicol (TAP) residues from the environment. The discovery of TAP-degrading bacteria and the decryption of its biodegradation mechanism will be beneficial to enhance the biological removal of TAP. In this study, Sphingomonas sp. CL5.1 was found to be capable of catabolizing TAP as the sole carbon, nitrogen, and energy source. This strain could degrade 93.9% of 25 mg/L TAP in 36 h, and remove about 11.9% of the total organic carbon of TAP. A novel metabolism pathway of TAP was constructed, and the enzymes involved in TAP metabolism in strain CL5.1 were predicted via proteomic and metabolic analysis. TAP was proposed to be transformed to O-TAP via oxidation of C₃-OH and DD-TAP via dehydration of C₃-OH and dehydrogenation of C₁-OH. A novel glucose-methanol-choline (GMC) family oxidoreductase CapO was predicted to be involved in the oxidation of C₃-OH. O-TAP was supposed to be further cleaved into DCA, glycine, and PMB. Glycine might be a pivotal direct nitrogen source for strain CL5.1, and it could be involved in nitrogen metabolism through the glycine cleavage system or directly participate in the biosynthetic processes.

Remediation of surface water contaminated by pathogenic microorganisms using calcium peroxide: Matrix effect, micro-mechanisms and morphological-physiological changes

Calcium peroxide (CaO₂), a common solid peroxide, has been increasingly used in contaminated site remediation due to its ability to release oxygen (O₂) and hydrogen peroxide (H₂O₂) and its environmental friendliness. Our present study is first to explore micromechnisms of CaO₂ to efficaciously inactivate pathogen indicators including gram-negative bacterium of Escherichia coli (E. coli), gram-positive bacterium of Staphylococcus aureus (S. aureus), and virus of Escherichia coli-specific M13 bacteriophage (VCSM13) under low concentration (≤ 4 mmol L^-1 (mM)). The inactivation mechanisms of E. coli, S. aureus (1 mmol L^-1 CaO₂) and VCSM13 (4 mmol L^-1) were mainly attributed to OH^- (32∼58%) and •OH (34∼42%), followed by H₂O₂ (13∼20%) and O₂^•- (10∼12%) generated from CaO₂, with the observed morphological and physiological-associated damages. Also, average steady-state concentrations of (OH^-, •OH, H₂O₂, and O₂^•-) and their reaction rate constants with E. coli and VCSM13 were determined. Accordingly, the micro-mechanism model of inactivation was established and validated, and the inactivation efficiency of the same order of magnitude of pathogen was predicted. Furthermore, during the common environmental factors, the copper ions was found to be promote CaO₂ inactivation of pathogens, and dissolved organic matter (DOM) fractions had a negative effect on CaO₂ inactivation. The present study explored the mechanisms of CaO₂ inactivation of pathogens in real surface water, laying the foundation for its potential use in the inactivation of water-borne microbial pathogens.

Rapid degradation of norfloxacin by VUV/Fe2+/H2O2 over a wide initial pH: Process parameters, synergistic mechanism, and influencing factors

Vacuum UV (VUV) technology has attracted much attention because it effectively splits water to generate reactive oxygen species (ROS) in situ and has the advantages of UV. So far, the synergistic mechanisms, formation pathways and contributions of ROS in VUV/Fe²⁺/H₂O₂ process have not been extensively studied. Herein, complete removal (at 4 min) and 63.3% mineralization (at 8 min) of 45 μM norfloxacin (NOR) were achieved at neutral pH by VUV/Fe²⁺/H₂O₂ (90 μM Fe²⁺ and 3 mM H₂O₂). Compared with its subsystems, VUV/Fe²⁺/H₂O₂ can not only increase the pseudo-first-order reaction rate constant of NOR removal by 2.3-14.9 times and increase the mineralization by 20.4-59.4%, but also reduce the residual ratio of H₂O₂ by 19.9-70.1% and reduce total cost by 20.0-68.0%. The synergy factor of VUV/Fe²⁺/H₂O₂ was 3.97, which was attributed to the VUV irradiation promoting iron redox cycle and H₂O₂ decomposition. Moreover, hydroxyl radical and superoxide radical, which were identified as the main ROS, contributed 79.07% and 18.47% to NOR removal, respectively. Degradation pathways of NOR were proposed. Furthermore, effects of coexisting ions and dissolved organic matter were investigated. As an energy-saving and efficient process, the satisfactory results of VUV/Fe²⁺/H₂O₂ applied in real waters also highlight its application potential.

A novel persulfate-photo-bioelectrochemical hybrid system promoting the degradation of refractory micropollutants at neutral pH

Bio-electro-Fenton is emerging as an alternative technology for the efficient and cost-effective removal of refractory micropollutants. Though promising, there are still several challenges that limit its wide application, including acidic operating conditions (pH at 2-3), the addition of supporting electrolytes (e.g., Na₂SO₄), and the issue of iron sludge generation. To address these challenges, a novel hybrid persulfate-photo-bioelectrochemical (PPBEC) system is proposed to remove model micropollutants (carbamazepine and clorfibric acid), from secondary effluent at low persulfate (PS) dosage and neutral pH. The effect of crucial operating parameters on the process was studied, including input voltage, cathodic aeration velocity, and PS dose. Under optimal conditions (0.6 V, 0.005 mL min^-1 mL^-1 and 1 mM), the PPBEC system achieved approx. 0.56-1.71 times greater micropollutant removal with 93% lower energy consumption when compared to the individual processes (UV/PS and PBEC). The improved performance was attributed to a faster production of sulfate radicals by UV irradiation, hydrogen peroxide activation and single-electron reduction, and hydroxyl radicals generated by UV irradiation. Furthermore, the transformation products of carbamazepine and clorfibric acid were identified and the probable pathways are proposed. Finally, the ecotoxicity of the PPBEC treated effluent was assessed by using Vibrio Fischeri, which exhibited a non-toxic effect.

Removal of a reactive dye from simulated textile wastewater by environmentally friendly oxidant calcium peroxide

In the present study, calcium peroxide (CaO2) was used separately for potential application as an environmentally friendly and low-cost oxidant for the removal of a textile dye ‘Reactive Black 5’ (RB5) from simulated textile wastewater containing auxiliary chemicals of textile production. The specific morphology, elemental analysis, particle size distribution, specific surface area, identification of crystalline phases and surface functional groups of the synthesized CaO2 were investigated by scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), laser diffraction (LD), Brunaure–Emmett–Teller method (BET), X-ray diffraction (XRD) and Fourier transmission infrared (FTIR), respectively. X-ray Diffraction analysis confirmed the synthesized oxidant as CaO2 with the tetragonal crystalline structure. The signal corresponded to a bending vibration of O–Ca–O was detected in the fingerprint region of the FTIR spectroscopy. The effects of various independent parameters such as contact time, pH, initial RB5 concentration and CaO2 dosage on decolorization were investigated. The results of the study showed that pH, initial dye concentration and the CaO2 amounts have significant effects on removal of the RB5. The optimum pH was determined 7 for the removal of RB5 by CaO2. 2.0 g CaO2 was found to be sufficient for the removal of 300 mg/L RB5 with 96.93% removal efficiency. Also 82.8% chemical oxygen demand (COD) removal efficiency from simulated textile wastewater (STW) was obtained by 2.0 g CaO2. The results of the present study showed that the CaO2 can be used as an environmentally friendly and low-cost oxidant for effective removal of reactive textile dyes.

Insights into enhanced biodegradation of sulfadimethoxine by catalyst: Transcriptomic responses and free radical interactions

The occurrence of sulfonamides in the environment is a severe global threat to public health due to the increasing prevalence of antibiotic selection pressure that may lead to the development of antibiotic resistance. We report an enhanced biodegradation of sulfadimethoxine (SDM) by Phanerochaete chrysosporium (Pc) with lignocellulosic biomass (Lb) using Fe₃O₄-ZSM-5 as a catalyst (Pc/Fe₃O₄-ZSM-5/Lb). SDM was completely degraded within 4 days at pH 7.0 in the Pc/Fe₃O₄-ZSM-5/Lb system. Transcriptomic, metabolites and free radical analyses were performed to explore the detailed molecular mechanisms of SDM degradation. A total of 246 genes of Pc in the Pc/Fe₃O₄-ZSM-5/Lb system exhibited significant upregulation compared to that in Pc alone. Upregulated genes encoding cellulases, cytochrome P450, cellobiose quinone oxidoreductase, and cellobiose dehydrogenase were involved in SDM degradation in the Pc/Fe₃O₄-ZSM-5/Lb system. In addition, genes encoding glutathione S-transferase and cytochrome P450 genes related to oxidative stress and detoxification were all significantly upregulated (P < 0.01). Electron paramagnetic resonance revealed the generation of OH suggesting a free radical pathway could be catalyzed by Fe₃O₄-ZSM-5 and the enzymes. These findings of catalyst-assisted SDM biodegradation will be valuable for remediation of antibiotics from contaminated wastewater.

Comparison of AOPs at pilot scale: Energy costs for micro-pollutants oxidation, disinfection by-products formation and pathogens inactivation

This work evaluated different advanced oxidation processes (AOPs) operated at pilot-scale as tertiary treatment of municipal wastewater in terms of energy efficiency, disinfection by-products formation and pathogens inactivation. Investigated AOPs included UV/H₂O₂, UV/Cl₂, O₃, O₃/UV, H₂O₂/O₃/UV, Cl₂/O₃/UV. AOPs were operated using various ozone doses (1.5-9 mg L^-1), and UV fluences (191-981 mJ cm^-2). Electrical energy costs necessary for the oxidation of contaminants of emerging concern (CEC) (i.e., carbamazepine, fluoxetine, gemfibrozil, primidone, sulfamethoxazole, trimethoprim) were calculated using the electrical energy per order (E_EO) parameter. Ozonation resulted by far the most energy efficient process, whereas UV/H₂O₂ and UV/Cl₂ showed the highest energy costs. Energy costs for AOPs based on the combination of UV and ozone were in the order O₃/UV ≈ Cl₂/O₃/UV > H₂O₂/O₃/UV, and they were significantly lower than energy costs of UV/H₂O₂ and UV/Cl₂ processes. Cl₂/O₃/UV increased bromate formation, O₃/UV and O₃ had same levels of bromate formation, whereas H₂O₂/O₃/UV did not form bromate. In addition, UV photolysis resulted an effective treatment for NDMA mitigation even in combination with ozone and chlorine in AOP technologies. Ozonation (doses of 1.5-6 mg L^-1) was the least effective process to inactivate somatic coliphages, total coliform, escherichia coli, and enterococci. UV irradiation was able to completely inactivate somatic coliphages, total coliform, escherichia coli at low fluence (191 mJ cm^-2), whereas enterococci were UV resistant. AOPs that utilized UV irradiation were the most effective processes for wastewater disinfection resulting in a complete inactivation of selected indicator organisms by low ozone dose (1.5 mg L^-1) and UV fluence (191-465 mJ cm^-2).

Comparison of the new Cl2/O3/UV process with different ozone- and UV-based AOPs for wastewater treatment at pilot scale: Removal of pharmaceuticals and changes in fluorescing organic matter

This work critically compared the removal of fluorescing PARAFAC components and selected pharmaceuticals (carbamazepine, fluoxetine, gemfibrozil, primidone, sulfamethoxazole, trimethoprim) from a tertiary wastewater effluent by different UV- and ozone-based advanced oxidation processes (AOPs) operated at pilot-scale. Investigated AOPs included UV/H₂O₂, UV/Cl₂, O₃, O₃/UV, H₂O₂/O₃/UV, and the new Cl₂/O₃/UV. AOPs comparison was accomplished using various ozone doses (0-9 mg/L), UV fluences (191-981 mJ/cm²) and radical promoter concentrations of Cl₂ = 0.04 mM and H₂O₂ = 0.29 mM. Chlorine-based AOPs produced radical species that reacted more selectively with pharmaceuticals than radical species and oxidants generated by other AOPs. Tryptophan-like substances and humic-like fluorescing compounds were the most degraded components by all AOPs, which were better removed than microbial products and fulvic-like fluorescing substances. Removal of UV absorbance at 254 (UV₂₅₄) nm was always low. Overall, chlorine-based AOPs were more effective to reduce fluorescence intensities than similar H₂O₂-based AOPs. The Cl₂/O₃/UV process was the most effective AOP to degrade all target micro-pollutants except primidone. On the other hand, the oxidation performance of pharmaceuticals by other ozone-based AOPs followed the order H₂O₂/O₃/UV > O₃/UV > O₃. UV/Cl₂ process outcompeted UV/H₂O₂ only for the removal of trimethoprim and sulfamethoxazole. Correlations between the removal of pharmaceuticals and spectroscopic indexes (PARAFAC components and UV₂₅₄) had unique regression parameters for each compound, surrogate parameter and oxidation process. Particularly, a diverse PARAFAC component for each investigated AOP resulted to be the most sensitive surrogate parameter able to monitor small changes of pharmaceuticals removal.

Pretreatment using UV combined with CaO2 for the anaerobic digestion of waste activated sludge: Mechanistic modeling for attenuation of trace organic contaminants

Trace organic contaminants (TOrCs) in waste active sludge (WAS) have caused many concerns due to their recalcitrance and detriment to the performance of anaerobic digestion (AD). In this study, UV (2 h) combined with calcium peroxide (CaO₂, 0.1 g g^-1-VSS (VSS, volatile suspended solid) was proposed as a suitable sludge pretreatment to enhance the AD performance with an increase in the production of maximum total short-chain fatty acids (421.3 %) and methane (119.2 %). Meanwhile, above 50 % removal efficiency for 19 detected TOrCs was achieved. UV and CaO₂ had a synergistic effect on the subsequent AD of WAS. Both UV and Ca(OH)₂ produced by CaO₂ played important roles in the dissolution of WAS and the subsequent AD, while UV-direct and OH-indirect photolysis accounted for TOrCs attenuation. In order to predict TOrCs attenuation by UV/CaO₂ treatment, a TOrCs photolysis model was tentatively established using carbamazepine as an indicator. This predictive model expressed a good prediction with adj-R² = 0.94, and the difference of predicted and measured values was within 27.3 %. This work evaluates a sludge pretreatment for simultaneously TOrCs attenuation and methane accumulation, laying foundation for promotion of sludge resource recycling.

The performance of chlorobenzene degradation in groundwater: comparison of hydrogen peroxide, nanoscale calcium peroxide and sodium percarbonate activated with ferrous iron

The chlorobenzene (CB) degradation performances by various oxidants, including hydrogen peroxide (H₂O₂), nanoscale calcium peroxide (nCaO₂) and sodium percarbonate (SPC), activated with ferrous iron (Fe(II)) were investigated and thoroughly compared. The results showed that all tested systems had strong abilities to degrade CB. The CB removal rate increased with increasing dosages of oxidants or Fe(II) because the generation of reactive oxygen species could be promoted with the chemical dosages' increase. Response surface and contour plots showed that CB could achieve a better removal performance at the same H₂O₂ and Fe(II) molar content, but the Fe(II) dosage was higher than that of oxidants in the nCaO₂ and SPC systems. The optimal molar ratios of H₂O₂/Fe(II)/CB, nCaO₂/Fe(II)/CB and SPC /Fe(II)/CB were 5.2/7.6/1, 8/8/1, and 4.5/8/1, respectively, in which 98.1%, 98%, and 96.4% CB removals could be obtained in 30 min reaction. The optimal pH condition was around 3, while CB removal rates were less than 20% in all three systems when the initial pH was adjusted to 9. The oxidative hydroxyl radicals (HO•) and singlet oxygen (¹O₂) had been detected by the electron paramagnetic resonance test. Based upon the results of liquid chromatograph-mass spectrometer analysis, the pathways of CB degradation were proposed, in which ¹O₂ roles were elaborated innovatively in the CB degradation mechanism. The CB degradation performance was significantly affected in actual groundwater, while increasing the molar ratio of oxidant/Fe(II)/CB was an effective way to overcome the adverse effects caused by the complex of actual groundwater matrix.

Predictive models for the degradation of 4 pharmaceutically active compounds in municipal wastewater effluents by the UV/H2O2 process

Pharmaceutically active compounds (PhACs) have been frequently detected in aquatic environment and raised concerns because of their environmental persistence and potential ecological risk, especially carbamazepine (CBZ), erythromycin (ERY), atenolol (ATL) and clofibric acid (CA). The UV/H₂O₂ advanced oxidation process was considered as an effective process to remove pharmaceuticals in wastewater. Because of the diverse structure of pharmaceuticals and the various wastewater matrices, this study established two models to predict the degradation of 4 PhACs in wastewater by UV/H₂O₂. Besides, the degradation pathway and toxicity of 4 PhACs by UV/H₂O₂ were explored. The degradation of 4 PhACs by UV/H₂O₂ followed the pseudo first-order kinetics pattern. The degradation rate of pharmaceuticals decreased as CBZ > ATL > CA > ERY. A kinetic model combining the steady state concentrations of HO∙ successfully predicted the degradation process of pharmaceuticals in 14 secondary municipal wastewater effluents. Also, a water matrix prediction model by response surface methodology (RSM) was established to estimate the degradation of pharmaceuticals well. A detailed and systematic comparison of two models in the objectives of models, predicting target contaminants, types of wastewater and parameters of models was made. In addition, the tentative transformation pathways of 4 PhACs by UV/H₂O₂ were proposed. 4 PhACs after UV/H₂O₂ treatment enhanced the toxicity, and prolongation of treatment time can reduce the toxicity on the luminescence.

Physico-chemical processes

By summarizing 187 relevant research articles published in 2019, the review is focused on the research progress of physicochemical processes for wastewater treatment. This review divides into two sections, physical processes and chemical processes. The physical processes section includes three sub-sections, that is, adsorption, granular filtration, and dissolved air flotation, whereas the chemical processes section has five sub-sections, that is, coagulation/flocculation, advanced oxidation processes, electrochemical, capacitive deionization, and ion exchange. PRACTITIONER POINTS: Totally 187 research articles on wastewater treatment have been reviewed and discussed. The review has two major sections with eight sub-topics.

Facile Construction of a Copper-Containing Covalent Bond for Peroxymonosulfate Activation: Efficient Redox Behavior of Copper Species via Electron Transfer Regulation

Heterogeneous catalysis can be enhanced through the construction of effective atom connection for rapid electron transport on the catalyst surface. Hence, this study proposed a new strategy for electron transfer regulation to facilitate redox cycle of Cu(II)/Cu(I). The objective was achieved by successful construction of copper-containing covalent bond through the in situ growth of porous g-C₃N₄ with oxygen dopants and nitrogen defects (O-CN_D) on CuAl_xO_y substrate (CuAl@O-CN_D). On the basis of X-ray absorption fine structure (XAFS) and other characterization results, the facilitated redox behavior of copper species by electron transfer regulation was ascribed to the formation of a C-O-Cu bond on the porous-rich superficial of the catalyst; these covalent C-O-Cu bonds shortened the migration distance of electrons between Cu(II) and Cu(I) via Cu(I)-O-C-O-Cu(II) bridge. The construction of copper-containing covalent bonds in the catalyst resulted in efficient PMS activation for a rapid redox cycle of Cu(II)/Cu(I), triggering a series of reactions involving the continuous production of three highly active species (SO₄^·-, ^·OH and ¹O₂). The rapid diffusion and transportation of the generated active species from porous structures directly attack typical pharmaceutically active compounds (PhACs), achieving superior catalytic performance. This study provides a new routine to construct a C-O-Cu bond for PMS activation by regulating the electron transfer to accelerate the redox behavior of copper species for environmental remediation.

In-situ dosage of Fe2+ catalyst using natural pyrite for thiamphenicol mineralization by photoelectro-Fenton process

The degradation of the antibiotic thiamphenicol has been studied by photoelectro-Fenton (PEF) process with UVA light using pyrite particles as catalyst source. Pyrite is a sulfide mineral that naturally acidifies the reaction medium and releases Fe²⁺, thus promoting the effective generation of OH from Fenton's reaction. The assays were made in an IrO₂/air-diffusion cell, which yielded similar results to a boron-doped diamond (BDD)/air-diffusion one at a lower cost. In dark conditions, electro-Fenton (EF) process showed an analogous ability for drug removal, but mineralization was much poorer because of the large persistence of highly stable by-products. Their photolysis explained the higher performance of PEF. Conventional homogeneous PEF directly using dissolved Fe²⁺ exhibited a lower mineralization power. This suggests the occurrence of heterogeneous Fenton's reaction over the pyrite surface. The effect of current density and drug content on pyrite-catalyzed PEF performance was examined. The drug heteroatoms were gradually converted into SO₄^2-, Cl^- and NO₃^- ions. Nine aromatic derivatives and two dichloroaliphatic amines were identified by GC-MS, and five short-chain carboxylic acids were detected by ion-exclusion HPLC. A reaction route for thiamphenicol mineralization by PEF process with continuous H₂O₂ and Fe²⁺ supply on site is proposed.

Comparison of aniline removal by UV/CaO2 and UV/H2O2: Degradation kinetics and mechanism

The instability and rapid consumption of H₂O₂ limit the application of UV/H₂O₂ in water treatment. Recently, calcium peroxide (CaO₂) has been demonstrated as an effective source of H₂O₂. However, the performance and mechanism of UV/CaO₂ are still unknown. Herein, UV/CaO₂ and UV/H₂O₂ were compared for degradation of aniline. The removal efficiency of aniline by UV/CaO₂ was slightly lower than that by UV/H₂O₂, which could be attributed to the light scavenger by CaO₂ suspended particles. HO‧ was identified to participate in aniline degradation in both UV/CaO₂ and UV/H₂O₂, while O₂^-· was only involved in UV/CaO₂. The efficiency of aniline degradation in UV/CaO₂ was affected by the released H₂O₂ in the system. The release and decomposition rate of H₂O₂ in UV/CaO₂ system were influenced by the CaO₂ dosage and reaction pH, but slightly related with water matrix. Excessive CaO₂ would scavenge aniline degradation through the released H₂O₂ to react with HO‧. Acidic condition would enhance the concentration of H₂O₂ in UV/CaO₂ and promote the degradation of aniline. Cl^- showed slight and almost no effect on aniline degradation in UV/CaO₂ and UV/H₂O₂ systems, respectively, while HCO₃^- scavenged aniline degradation in UV/CaO₂. NO₃^- inhibited aniline degradation in both UV/CaO₂ and UV/H₂O₂. Compared to UV/H₂O₂, UV/CaO₂ shows the similar efficiency on organics removal but conquers the limitations in UV/H₂O₂, which is a promising alternative choice in water treatment.