Micropollutants removal by full-scale UV-C/sulfate radical based Advanced Oxidation Processes

Environmental impact and source-controlled approaches for emerging micropollutants: Current status and future prospects

Emerging micropollutants, originating from diverse sources, including pharmaceutical, pesticides, and industrial effluents, are a serious environmental concern. Their presence in natural water bodies has negative effects on ecosystems and human health. To address this issue, the importance of a source-controlled approach has grown, highlighting the use of advanced technologies such as oxidation processes, membrane filtration, and adsorption to prevent micropollutants from entering the environment. Therefore, this review provides a comprehensive overview of emerging micropollutants, their analytical detection methods, and their environmental impacts, with a focus on aquatic ecosystems, human health, and terrestrial environments. It also highlights the importance of using a source-controlled approach and provides insights into the benefits and drawbacks of this strategy. The primary micropollutants identified in this review were erythromycin, ibuprofen, and triclocarban, originating from the pharmaceutical industries for their use as antibiotics, analgesic, and antibacterial drugs. The primary analytical methods used for detection involved hybrid techniques that integrate chromatography with spectroscopy. Thus, this review emphasizes the source-controlled approach's benefits and drawbacks, focusing on emerging micropollutants, their detection, and impacts on ecosystems and health.

Integrated electrochemical-adsorption for simultaneous removal of pharmaceuticals from water: Process optimization and synergistic insights

Water contamination with pharmaceuticals has become an evident environmental challenge. Treatment processes such as electrochemical oxidation (EO) and adsorption have limitations in the simultaneous removal of pharmaceuticals from water. Therefore, this study examined the potential of coupled process (EO followed by adsorption) in binary pharmaceuticals (acetaminophen (ACM) + ciprofloxacin (CIP)) removal from water, with an emphasis on coupled process optimization. Consequently, optimized coupled process conditions including current density (22 mA/cm2), pH (5.5), EO time (40 min), adsorbent dose (0.1 g/L) and adsorption time (60 min) were obtained. Under optimal conditions, removal efficiencies of 94.6% (ACM)+92% (CIP), 94.07% (ACM)+91.15% (CIP), and > 99.8% (ACM + CIP) were recorded for 20 mg/L (ACM + CIP) removal in EO, adsorption and EO + adsorption, respectively. Further, the coupled process was employed in multiple pharmaceuticals (20 mg/L of ACM + CIP + ATN (atenolol) + AMX (amoxicillin)) removal from water and removal of > 97.56% (ACM + CIP + ATN + AMX) was achieved. Removal efficiencies of ACM (83.35%) + CIP (73.1%) + ATN (68.52%) + AMX (63.05%) and ACM (80.37%) + CIP (66.5%) + ATN (73.07%) + AMX (60.5%) were obtained in EO and adsorption, respectively. The noted lower removal efficiencies in EO and adsorption are associated with the diverse nature of the pharmaceuticals, limited adsorbent active sites, and the shared utilization of reactive oxygen species (ROS) among the pharmaceuticals in EO. The total organic carbon (TOC) removal of 40.24%, and 99% and chemical oxygen demand (COD) removal of 72.45%, and 99.6% were obtained under optimal conditions of EO, and coupled process, respectively. These findings indicate that the pharmaceuticals are only partially mineralized in EO and the subsequent adsorption effectively eliminated the remaining target pharmaceuticals, and degradation by-products from water. Additionally, integrating EO with adsorption reduced the electrical energy consumption of the EO process from 31.6 kWh/m³ to 6 kWh/m³ under optimal conditions. Overall, coupling EO with adsorption offers the utmost advantages when removing multiple pharmaceuticals from complex water matrices.

Insights into the transformation of natural organic matter during UV/peroxydisulfate treatment by FT-ICR MS and machine learning: Non-negligible formation of organosulfates

Natural organic matter (NOM) is a major sink of radicals in advanced oxidation processes (AOPs) and understanding the transformation of NOM is important in water treatment. By using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) in conjunction with machine learning, we comprehensively investigated the reactivity and transformation of NOM, and the formation of organosulfates during the UV/peroxydisulfate (PDS) process. After 60 min UV/PDS treatment, the CHO formula number and dissolved organic carbon concentration significantly decreased by 83.4 % and 74.8 %, respectively. Concurrently, the CHOS formula number increased substantially from 0.7 % to 20.5 %. Machine learning identifies DBE and AImod as the critical characteristics determining the reactivity of NOM during UV/PDS treatment. Furthermore, linkage analysis suggests that decarboxylation and dealkylation reactions are dominant transformation pathways, while the additions of SO3 and SO4 are also non-negligible. According to SHAP analysis, the m/z, number of oxygens, DBE and O/C of NOM were positively correlated with the formation of organosulfates in UV/PDS process. 92 organosulfates were screened out by precursor ion scan of HPLC-MS/MS and verified by UPLC-Q-TOF-MS, among which, 7 organosufates were quantified by authentic standards with the highest concentrations ranging from 2.1 to 203.0 ng L‒1. In addition, the cytotoxicity of NOM to Chinese Hamster Ovary (CHO) cells increased by 13.8 % after 30 min UV/PDS treatment, likely responsible for the formation of organosulfates. This is the first study to employ FT-ICR MS combined with machine learning to identify the dominant NOM properties affecting its reactivity and confirmed the formation of organosulfates from sulfate radical oxidation of NOM.

What is the role of nitrate/nitrite in trace organic contaminants degradation and transformation during UV-based advanced oxidation processes?

The effectiveness of UV-based advanced oxidation processes (UV-AOPs) in degrading trace organic contaminants (TrOCs) can be significantly influenced by the ubiquitous presence of nitrate (NO3-) and nitrite (NO2-) in water and wastewater. Indeed, NO3-/NO2- can play multiple roles of NO3-/NO2- in UV-AOPs, leading to complexities and conflicting results observed in existing research. They can inhibit the degradation of TrOCs by scavenging reactive species and/or competitively absorbing UV light. Conversely, they can also enhance the elimination of TrOCs by generating additional •OH and reactive nitrogen species (RNS). Furthermore, the presence of NO3-/NO2- during UV-AOP treatment can affect the transformation pathways of TrOCs, potentially resulting in the nitration/nitrosation of TrOCs. The resulting nitro(so)-products are generally more toxic than the parent TrOCs and may become precursors of nitrogenous disinfection byproducts (N-DBPs) upon chlorination. Particularly, since the impact of NO3-/NO2- in UV-AOPs is largely due to the generation of RNS from NO3-/NO2- including NO•, NO2•, and peroxynitrite (ONOO-/ONOOH), this review covers the generation, properties, and detection methods of these RNS. From kinetic, mechanistic, and toxicologic perspectives, future research needs are proposed to advance the understanding of how NO3-/NO2- can be exploited to improve the performance of UV-AOPs treating TrOCs. This critical review provides a comprehensive framework outlining the multifaceted impact of NO3-/NO2- in UV-AOPs, contributing insights for basic research and practical applications of UV-AOPs containing NO3-/NO2-.

Degradation of Ampicillin with antibiotic activity removal using persulfate and submersible UVC LED: Kinetics, mechanism, electrical energy and cost analysis

Effective water treatment to remove antibiotics and its activity from contaminated water is urgently needed to prevent antibiotic-resistant bacteria (ARB) emergence. In this study, we investigated degradation of Ampicillin (AMP), an extensively used β-lactam antibiotic, using submersible Ultraviolet C Light Emitting Diode (λmax = 276 nm) irradiation source, and Persulfate (UVC LED/PS system). Pseudo first order rate constant (kobs) for degradation of AMP (1 ppm) by UVC LED/PS system was determined to be 0.5133 min-1 (PS = 0.2 mM). kobs value at pH 2.5 (0.7259 min-1) was found to be higher than pH 6.5 (0.5133 min-1) and pH 12 (0.1745 min-1). kobs value for degradation of AMP in deionized water spiked with inorganic anions (Cl-=0.5369 min-1,SO42-=0.4545 min-1, NO3-=0.1526 min-1, HCO3-=0.0226 min-1), in real tap water (0.1182 min-1) and simulated ground water (0.0372 min-1) were presented. Radical scavenging experiment reveal involvement of sulfate radical anion and hydroxyl radical in UVC LED/PS system. EPR analysis confirms the generation of sulfate radical anion and hydroxyl radical. Importantly, 74% reduction of total organic carbon (TOC) occurred within 60 min of AMP treatment by UVC LED/PS system. Seven degradation by-products were identified by high resolution mass spectrometry, and degradation pathways were proposed. Antibacterial activity of AMP towards Bacillus subtilis and Staphylococcus aureus was completely removed after UVC LED/PS treatment. ECOSAR model predicted no very toxic degradation by-products generation by UVC LED/PS system. Electrical Energy per order (EEo) and cost of UVC LED/PS system were determined to be 0.9351 kW/m3/order and ₹ 7.91/m3 ($ 0.095/m3 or € 0.087/m3), respectively. Overall, this study highlights, UVC LED/PS system as energy efficient, low-cost, and its potential to emerge as sulfate radical anion based advanced oxidation process (AOP) to treat water with antibiotics.

Efficacious degradation of ethylene glycol by ultraviolet activated persulphate: reaction kinetics, transformation mechanisms, energy demand, and toxicity assessment

Ethylene glycol or 1,2-ethanediol (EG) is a persistent and toxic substance in the environment and extensively applied in petrochemical, surfactants, antifreeze, asphalt emulsion paints, cosmetics, plastics, and polyester fiber industries. Degradation of EG by using ultraviolet (UV) activated hydrogen peroxide (H2O2) and persulfate (PS) or persulfate anion (S2O82-) based advanced oxidation processes (AOPs) were explored. The result obtained demonstrate that UV/PS (85.7 ± 2.5%) has exhibited improved degradation efficiency of EG as compared to UV/H2O2 (40.4 ± 3.2%) at optimal operating conditions of 24 mM of EG concentration, 5 mM of H2O2, 5 mM of PS, 1.02 mW cm-2 of UV fluence, and pH of 7.0. Impacts of operating factors, including initial EG concentration, oxidant dosage, reaction duration, and the impact of different water quality parameters, were also explored in this present investigation. The degradation of EG in Milli-Q® water followed pseudo - first order reaction kinetics in both methods having a rate constant of about 0.070 min-1 and 0.243 min-1 for UV/H2O2 and UV/PS, respectively, at optimum operating conditions. Additionally, an economic assessment was also conducted under optimal experimental conditions, and the electrical energy per order and total operational cost for treating per m3 of EG-laden wastewater was observed to be about 0.042 kWh m-3 order-1 and 0.221 $ m-3 order-1, respectively, for UV/PS, which was slightly lower than UV/H2O2 (0.146 kWh m-3 order-1; 0.233 $ m-3 order-1). The potential degradation mechanisms were proposed based on intermediate by-products detected by Fourier transform infrared (FTIR) spectroscopy and gas chromatography-mass spectroscopy (GC-MS). Moreover, real petrochemical effluent containing EG was also treated by UV/PS, demonstrating 74.7 ± 3.8% of EG and 40.7 ± 2.6% of total organic carbon removal at 5 mM of PS and 1.02 mW cm-2 of UV fluence. A toxicity tests on Escherichia coli (E. coli) and Vigna radiata (green gram) confirmed non-toxic nature of UV/PS treated water.

UV-activated persulfates oxidation of anthraquinone dye: Kinetics and ecotoxicological assessment

Sulfate radical-based advanced oxidation processes (SR-AOPs) are gaining popularity as a feasible alternative for removing recalcitrant pollutants in an aqueous environment. Persulfates, namely peroxydisulfate (PDS) and peroxymonosulfate (PMS) are the most common sulfate radical donors. Persulfates activation by ultraviolet (UV) irradiation is considered feasible due to the high concentration of radicals produced as well as the lack of catalysts leaching. The research focuses on determining the impact of activated PDS and PMS on the degradation of anthraquinone dye, i.e., Acid Blue 129 (AB129). UV-activated PDS and PMS can quickly degrade the AB129 as well as restrict the formation of by-products. This could explain the reduced ecotoxicity levels of the treated water after degradation, using an aquatic plant (Lemna minor) and a crustacean (Daphnia magna). This, on the other hand, can ensure that the sulfate radical-based processes can be an environmentally friendly technology.

Efficient mitigation of emerging antibiotics residues from water matrix: Integrated approaches and sustainable technologies

The prevalence of antibiotic traces in the aquatic matrices is a concern due to the emanation of antibiotic resistance which requires a multifaceted approach. One of the potential sources is the wastewater treatment plants with a lack of advance infrastructure leading to the dissemination of contaminants. Continuous advancements in economic globalization have facilitated the application of several conventional, advanced, and hybrid techniques for the mitigation of rising antibiotic traces in the aquatic matrices that have been thoroughly scrutinized in the current paper. Although the implementation of existing mitigation techniques is associated with several limiting factors and barriers which require further research to enhance their removal efficiency. The review further summarizes the application of the microbial processes to combat antibiotic persistence in wastewater establishing a sustainable approach. However, hybrid technologies are considered as most efficient and environmental-benign due to their higher removal efficacy, energy-efficiency, and cost-effectiveness. A brief elucidation has been provided for the mechanism responsible for lowering antibiotic concentration in wastewater through biodegradation and biotransformation. Overall, the current review presents a comprehensive approach for antibiotic mitigation using existing methods however, policies and measures should be implemented for continuous monitoring and surveillance of antibiotic persistence in aquatic matrices to reduce their potential risk to humans and the environment.

Recent innovations and challenges in the eradication of emerging contaminants from aquatic systems

Presence of emerging pollutants (EPs), aka Micropollutants (MPs) in the freshwater environments is a severe threat to the environment and human beings. They include pharmaceuticals, insecticides, industrial chemicals, natural hormones, and personal care items and the pollutants are mostly present in wastewater generated from urbanization and increased industrial growth. Even concentrations as low as ngL^-1 or mgL^-1 have proven ecologically lethal to aquatic biota. For several years, the biodegradation of various Micropollutants (MPs) in aquatic ecosystems has been a significant area of research worldwide, with many chemical compounds being discovered in various water bodies. As aquatic biota spends most of their formative phases in polluted water, the impacts on aquatic biota are obvious, indicating that the environmental danger is substantial. In contrast, the impact of these contaminants on aquatic creatures and freshwater consumption is more subtle and manifests directly when disrupting the endocrine system. Research and development activities are expected to enable the development of ecologically sustainable, cost-effective, and efficient treatments for practical systems in the near future. Therefore, this review aims to understand recent emerging pollutants discovered and the available treatment technologies and suggest an innovative and cost-effective method to treat these EPs, which is sustainable and follows the circular bioeconomy.

Aquatic photolysis of high-risk chemicals of emerging concern from secondary effluent mediated by sunlight irradiation for ecological safety and the enhanced methods

Natural sunlight can reduce the chemicals of emerging concern (CECs) and biological effects from the discharged domestic wastewater. But the aquatic photolysis and biotoxic variations of specific CECs detected in secondary effluent (SE) were not clear. In this study, 29 CECs were detected in the SE, and 13 medium- and high-risk CECs were identified as target chemicals based on their ecological risk assessment. To comprehensively explore the photolysis properties of the identified target chemicals, the direct and self-sensitized photodegradation of the target chemicals, even the indirect photodegradation in the mixture, were investigated and compared with these photodegradation in the SE. Of the 13 target chemicals, only five chemicals (including dichlorvos (DDVP), mefenamic acid (MEF), diphenhydramine hydrochloride (DPH), chlorpyrifos (CPF), and imidacloprid (IMI)) underwent direct and self-sensitized photodegradation processes. The removal of DDVP, MEF, and DPH was attributed to self-sensitized photodegradation, which was mainly mediated by •OH; CPF and IMI primarily relied on direct photodegradation. Synergistic and/or antagonistic actions that occurred in the mixture improved/decreased the rate constants of five photodegradable target chemicals. Meanwhile, the biotoxicities (acute toxicity and genotoxicity) of the target chemicals (including individual chemicals and the mixture) were significantly reduced, which can explain the reduction of biotoxicities from SE. For the two refractory high-risk chemicals, atrazine (ATZ) and carbendazim (MBC), algae-derived intracellular dissolved organic matter (IOM) on ATZ, and IOM and extracellular dissolved organic matter (EOM) on MBC had slightly promotion for their photodegradation; while peroxysulfate, and peroxymonosulfate served as sensitizers were activated by natural sunlight and effectively improved their photodegradation rate, and then reduced their biotoxicities. These findings will promote the development of CECs treatment technologies based on sunlight irradiation.

Core-shell magnetic CFO@COF composites toward peroxymonosulfate activation for degradation of sulfamethoxazole from aqueous solution: A comparative study and mechanistic consideration

A core-shell covalent organic framework encapsulated Co1.2Fe1.8O4 magnetic particles (CFO@COF) was designed and prepared successfully to activate peroxymonosulfate (PMS) for sulfamethoxazole (SMX) degradation. It displays amazing catalytic reactivity since the unique interior structure and synergistic effect between COF shell and CFO core, reaching 99.8% removal of SMX (10 mg/L) within 30 min and 90.8% TOC removal. The synergy between bimetals vests high reactivity to CFO core. And the outer COF shell can stabilize the CFO core under intricate reaction conditions to restrain the leaching of Co ions (decreased from 0.75 to 0.25 mg/L). Further investigation compared the activation mechanism in two different system, CFO/PMS system and CFO@COF/PMS system. The result showed that the radical mechanism controlled by SO4⋅- guided the SMX degradation in CFO/PMS system whereas the 1O2 played a pivotal role in CFO@COF/PMS system called non-radical leading. The influences of various factors on degradation experiments and SMX degradation pathway were also studied. Most importantly, risk assessment in CFO@COF/PMS/SMX system was estimated via "ecological structure activity relationships". In most case, the toxicities of intermediates were lower than the initial samples, which confirmed the effectiveness of CFO@COF/PMS/SMX system in the reduction of toxicity of SMX.

Advanced oxidation processes: Performance, advantages, and scale-up of emerging technologies

Advanced oxidation processes (AOPs) are promising technologies for partial or complete mineralization of contaminants of emerging concern by highly reactive hydroxyl, hydroperoxyl, superoxide, and sulphate radicals. Detailed investigations and reviews have been reported for conventional AOP systems that have been installed in full-scale wastewater treatment plants. However, recent efforts have focused on the peroxymonosulphate, persulphate, catalytic ozonation, ultrasonication and hydrodynamic cavitation, gamma radiation, electrochemical oxidation, modified Fenton, and plasma-assisted AOPs. This critical review presents the detailed mechanisms of emerging AOP technologies, their performance for treatment of contaminants of emerging concern, the relative advantages and disadvantages of each technology, and the remaining challenges to scale-up and implementation. Among the evaluated technologies, the modified electrochemical oxidation, gamma radiation, and plasma-assisted systems demonstrated the greatest potential for successful and sustainable implementation in wastewater treatment due to their environmental safety, compatibility, and efficient transformation of contaminants of emerging concern by a variety of reactive species. The other emerging AOP systems were also promising, but additional scale-up trials and a deeper understanding of their reaction kinetics in complex wastewater matrices are necessary to determine the technical and economic feasibility of full-scale processes.

Sulfate radical based advanced oxidation processes for agro-industrial effluents treatment: A comparative review with Fenton's peroxidation

Agro-industrial wastewater management becomes a major task while environmental regulations are becoming stricter worldwide. Agro-industrial wastewaters are known by high content of organic pollutants that cause an adverse effect on the water bodies. Industries are looking for efficient, easy-to-use and affordable treatment processes. Sulfate radical based advanced oxidation processes (S-AOPs) are arising as suitable alternatives for agro-industrial effluents treatment. In this review, the major findings regarding the application of this technology for real agro-industrial wastewater depuration are discussed. Moreover, these technologies are compared as an alternative to Fenton's process, which is a widely studied advanced oxidation process and with high efficiency in the treatment of agro-industrial effluents. The studies already carried out are promising, but there is still a great lack of studies in this area and using this technique.

A new and systematic review on the efficiency and mechanism of different techniques for OPFRs removal from aqueous environments

Organic phosphorus flame retardants (OPFRs), as a new type of emerging contaminant, have drawn great attention over the last few years, due to their wide distribution in aquatic environments and potential toxicities to humans and living beings. Various treatment methods have been reported to remove OPFRs from water or wastewater. In this review, the performances and mechanisms for OPFRs removal with different methods including adsorption, oxidation, reduction and biological techniques are overviewed and discussed. Each technique possesses its advantage and limitation, which is compared in the paper. The degradation pathways of typical OPFRs pollutants, such as Cl-OPFRs, alkyl OPFRs and aryl OPFRs, are also reviewed and compared. The degradation of those OPFRs depends heavily upon their structures and properties. Furthermore, the implications and future perspectives in such area are discussed. The review may help identify the research priorities for OPFRs remediation and understand the fate of OPFRs during the treatment processes.

State-of-the-Art Review on the Application of Membrane Bioreactors for Molecular Micro-Contaminant Removal from Aquatic Environment

In recent years, the emergence of disparate micro-contaminants in aquatic environments such as water/wastewater sources has eventuated in serious concerns about humans’ health all over the world. Membrane bioreactor (MBR) is considered a noteworthy membrane-based technology, and has been recently of great interest for the removal micro-contaminants. The prominent objective of this review paper is to provide a state-of-the-art review on the potential utilization of MBRs in the field of wastewater treatment and micro-contaminant removal from aquatic/non-aquatic environments. Moreover, the operational advantages of MBRs compared to other traditional technologies in removing disparate sorts of micro-contaminants are discussed to study the ways to increase the sustainability of a clean water supplement. Additionally, common types of micro-contaminants in water/wastewater sources are introduced and their potential detriments on humans’ well-being are presented to inform expert readers about the necessity of micro-contaminant removal. Eventually, operational challenges towards the industrial application of MBRs are presented and the authors discuss feasible future perspectives and suitable solutions to overcome these challenges.

Selecting the most environmentally friendly oxidant for UVC degradation of micropollutants in urban wastewater by assessing life cycle impacts: Hydrogen peroxide, peroxymonosulfate or persulfate?

The quality of water bodies has been decreasing over time. Urban wastewater treatment plants (UWWTPs) are key players to avoid that potentially toxic micropollutants reach the environment, and advanced treatment processes are being applied to address this issue. However, several variables have to be taken into account, particularly environmental sustainability. The aim of this study is to assess the life cycle impacts of combining UVC with different oxidants - hydrogen peroxide (H₂O₂), peroxymonosulfate (PMS) and persulfate (PS) -, considering different concentrations (0.05, 0.20 and 0.50 mM) and UVC dosages of 42, 63 and 170 J/L, corresponding to UV contact times of 4, 7 and 18 s in a specific industrial equipment. UVC/PMS was the worst performing process (despite being able to achieve removals similar to UVC/H₂O₂), followed by UVC/PS. Both would only be preferred relatively to H₂O₂ if much lower concentrations of PMS or PS could be used to achieve the same removal of micropollutants (10 times lower was not enough). Additionally, PMS and PS production contributes more to the environmental footprint than the electricity use, unlike H₂O₂. Therefore even if considering lower treatment times when using sulfate-based oxidants, these will still be more impactful than using H₂O₂ at the studied conditions. Based on both avoided and generated impacts, H₂O₂ is the best option environmentally. In this case, the environmental impacts are more affected by an increase in treatment time rather than by an increase in the H₂O₂ concentration. It is thus best to opt for a higher concentration and the lowest treatment time possible for a significant ecotoxicity reduction. Electricity is a relevant parameter in all cases and its impact can be reduced in nearly all endpoint categories by opting for cleaner energy sources.

Mixtures of chelating agents to enhance photo-Fenton process at natural pH: Influence of wastewater matrix on micropollutant removal and bacterial inactivation

Three organic fertilizers (EDTA (Ethylenedinitrilotetraacetic acid), EDDS (Ethylenediamine-N, N'-disuccinic acid) and DTPA (Diethylene triamine pentaacetic acid)) were tested as Fe-complexes in photo-Fenton process at natural pH for micropollutants (MPs) abatement and simultaneous E.coli inactivation. Less stable Fe-complexes show high iron precipitation, stopping MPs degradation. On the contrary, stable Fe-complexes imply low kinetic rates for MPs removal. To solve these inconveniences, three mixtures of organic fertilizers were also tested, trying to improve the kinetic rates of micropollutants oxidation and overcome iron precipitation. Three different pollutants (propranolol (PROP), acetamiprid (ACMP) and sulfamethoxazole (SMX)) were used as the target compounds. As the iron release is, in part, linked to the hardness of water, two water matrices from two different secondary wastewaters (Membrane Bioreactor (MBR) and Conventional Activated Sludge (CAS)) were tested. The best performance in micropollutant degradation and E.coli inactivation was achieved with the combination of EDDS + EDTA, accomplishing a good equilibrium between iron precipitation and rate of MPs removal. For instance, total removal of propranolol was achieved at 45 min in MBR, while it was only 85.7% in CAS, being an improvement of the process comparing with that obtained using single organic fertilizers. At the end of the treatment, 2.1 log-inactivation for E.coli was reached in CAS. The differences observed between both wastewaters were related to CAS' higher DOC, turbidity, and hardness. Finally, from the physicochemical characterization conducted, including Biochemical Oxygen Demand at 5 days and phytotoxicity, it is possible to highlight the suitability of these treated effluents for its reuse in irrigation, as long as in CAS matrix the final values of E. coli are within the legal limit.

Combat of antimicrobial resistance in municipal wastewater treatment plant effluent via solar advanced oxidation processes: Achievements and perspectives

This review aims to gather main achievements and limitations associated to the application of solar photocatalytic processes with regard to the removal of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) from municipal wastewater treatment plant effluent (MWWTPE). Solar photocatalytic processes were chosen considering the context of developing tropical countries. Among these processes, solar photo-Fenton has been proved effective for the elimination of ARB from MWWTPE at neutral pH in bench and pilot scale and also under continuous flow. Yet, ARG removal varies as according to the gene. Irradiation intensity and matrix composition play a key role on treatment efficiency for this purpose. The use of sulfate radical in modified solar photo-Fenton is still incipient for ARB and ARG removal. Also, investigations related to ARB resistance profile and horizontal gene transfer rates after solar photo-Fenton treatment must be further analyzed. Regarding solar heterogeneous photocatalysis, TiO₂ and TiO₂-composites applied in suspension are the most commonly investigated for the removal of ARB and ARGs. Irradiation intensity, temperature and catalyst dosage affect treatment efficiency. However, most studies were performed in synthetic solutions using reduced sample volumes. Extended exposition times and addition of H₂O₂ to the system (solar/TiO₂/H₂O₂) are required to prevent bacteria regrowth and ensure ARG abatement. In addition, enhancement of TiO₂ with graphene or (semi)metals improved ARB elimination. Differences concerning irradiation intensity, matrix composition, catalyst dosage, and model ARB and ARGs used in studies analyzed in this review hinder the comparison of photocatalysts synthesized by various research groups. Finally, future research should aim at evaluating the efficiency of solar photocatalytic processes in real matrices originated from sewage treatment systems applied in developing countries; determining indicators of antimicrobial resistance in MWWTPE; and investigating ARB mutation rate as well as the removal of cell-free ARGs present in suspension in MWWTPE.

UV-C Peroxymonosulfate Activation for Wastewater Regeneration: Simultaneous Inactivation of Pathogens and Degradation of Contaminants of Emerging Concern

This study explores the capability of Sulfate Radical-based Advanced Oxidation Processes (SR-AOPs) for the simultaneous disinfection and decontamination of urban wastewater. Sulfate and hydroxyl radicals in solution were generated activating peroxymonosulfate (PMS) under UV-C irradiation at pilot plant scale. The efficiency of the process was assessed toward the removal of three CECs (Trimethoprim (TMP), Sulfamethoxazole (SMX), and Diclofenac (DCF)) and three bacteria (Escherichia coli, Enterococcus spp., and Pseudomonas spp.) in actual urban wastewater (UWW), obtaining the optimal value of PMS at 0.5 mmol/L. Under such experimental conditions, bacterial concentration ≤ 10 CFU/100 mL was reached after 15 min of UV-C treatment (0.03 kJ/L of accumulative UV-C radiation) for natural occurring bacteria, no bacterial regrowth was observed after 24 and 48 h, and 80% removal of total CECs was achieved after 12 min (0.03 kJ/L), with a release of sulfate ions far from the limit established in wastewater discharge. Moreover, the inactivation of Ampicillin (AMP), Ciprofloxacin (CPX), and Trimethoprim (TMP) antibiotic-resistant bacteria (ARB) and reduction of target genes (ARGs) were successfully achieved. Finally, a harmful effect toward the receiving aquatic environment was not observed according to Aliivibrio fischeri toxicity tests, while a slightly toxic effect toward plant growth (phytotoxicity tests) was detected. As a conclusion, a cost analysis demonstrated that the process could be feasible and a promising alternative to successfully address wastewater reuse challenges.

UV-A activation of peroxymonosulfate for the removal of micropollutants from secondary treated wastewater

The occurrence of micropollutants (MPs) in the aquatic environment poses a threat to the environment and to the human health. The application of sulfate radical-based advanced oxidation processes (SR-AOPs) to eliminate these contaminants has attracted attention in recent years. In this work, the simultaneous degradation of 20 multi-class MPs (classified into 5 main categories, namely antibiotics, beta-blockers, other pharmaceuticals, pesticides, and herbicides) was evaluated for the first time in secondary treated wastewater, by activating peroxymonosulfate (PMS) with UV-A radiation, without any pH adjustment or iron addition. The optimal PMS concentration to remove the spiked target MPs (100 μg L^-1) from wastewater was 0.1 mM, leading to an average degradation of 80% after 60 min, with most of the elimination occurring during the first 5 min. Synergies between radiation and the oxidant were demonstrated and quantified, with an average extent of synergy of 69.1%. The optimized treatment was then tested using non-spiked wastewater, in which 12 out of the 20 target contaminants were detected. Among these, 7 were degraded at some extent, varying from 10.7% (acetamiprid) to 94.4% (ofloxacin), the lower removals being attributed to the quite inferior ratio of MPs to natural organic matter. Phytotoxicity tests carried out with the wastewater before and after photo-activated PMS oxidation revealed a decrease in the toxicity and that the plants were able to grow in the presence of the treated water. Therefore, despite the low degradation rates obtained for some MPs, the treatment effectively reduces the toxicity of the matrix, making the water safer for reuse.

Peracetic acid-based advanced oxidation processes for decontamination and disinfection of water: A review

Peracetic acid (PAA) has attracted growing attention as an alternative oxidant and disinfectant in wastewater treatment due to the increased demand to reduce chlorine usage and control disinfection byproducts (DBPs). These applications have stimulated new investigations on PAA-based advanced oxidation processes (AOPs), which can enhance water disinfection and remove micropollutants. The purpose of this review is to conduct a comprehensive analysis of scientific information and experimental data reported in recent years on the applications of PAA-based AOPs for the removal of chemical and microbiological micropollutants from water and wastewater. Various methods of PAA activation, including the supply of external energy and metal/metal-free catalysts, as well as their activation mechanisms are discussed. Then, a review on the usage of PAA-based AOPs for contaminant degradation is given. The degradation mechanisms of organic compounds and the influence of the controlling parameters of PAA-based treatment systems are summarized and discussed. Concurrently, the application of PAA-based AOPs for water disinfection and the related mechanisms of microorganism inactivation are also reviewed. Since combining UV light with PAA is the most commonly investigated PAA-based AOP for simultaneous pathogen inactivation and micropollutant oxidation, we have also focused on PAA microbial inactivation kinetics, together with the effects of key experimental parameters on the process. Moreover, we have discussed the advantages and disadvantages of UV/PAA as an AOP against the well-known and established UV/H₂O₂. Finally, the knowledge gaps, challenges, and new opportunities for research in this field are discussed. This critical review will facilitate an in-depth understanding of the PAA-based AOPs for water and wastewater treatment and provide useful perspectives for future research and development for PAA-based technologies.

Towards the Implementation of Circular Economy in the Wastewater Sector: Challenges and Opportunities

The advancement of science has facilitated increase in the human lifespan, reflected in economic and population growth, which unfortunately leads to increased exploitation of resources. This situation entails not only depletion of resources, but also increases environmental pollution, mainly due to atmospheric emissions, wastewater effluents, and solid wastes. In this scenario, it is compulsory to adopt a paradigm change, as far as the consumption of resources by the population is concerned, to achieve a circular economy. The recovery and reuse of resources are key points, leading to a decrease in the consumption of raw materials, waste reduction, and improvement of energy efficiency. This is the reason why the concept of the circular economy can be applied in any industrial activity, including the wastewater treatment sector. With this in view, this review manuscript focuses on demonstrating the challenges and opportunities in applying a circular economy in the water sector. For example, reclamation and reuse of wastewater to increase water resources, by paying particular attention to the risks for human health, recovery of nutrients, or highly added-value products (e.g., metals and biomolecules among others), valorisation of sewage sludge, and/or recovery of energy. Being aware of this situation, in the European, Union 18 out of 27 countries are already reusing reclaimed wastewater at some level. Moreover, many wastewater treatment plants have reached energy self-sufficiency, producing up to 150% of their energy requirements. Unfortunately, many of the opportunities presented in this work are far from becoming a reality. Still, the first step is always to become aware of the problem and work on optimizing the solution to make it possible.

Activation of persulfate by stability-enhanced magnetic graphene oxide for the removal of 2,4-dichlorophenol

A stability-enhanced magnetic catalyst, composed of α-Fe₂O₃@Fe₃O₄ shell-core magnetic nanoparticles and graphene oxide (MGO), was prepared and characterized by scanning electron micrope (SEM), X-ray diffraction (XRD), vibrating sample magnetometer (VSM), and Brunauer-Emmett-Teller (BET). Catalyst synthesis was used to efficiently activate persulfate for the removal of 2,4-dichlorophenol (2,4-DCP). A magnetic nanoparticle:GO mass ratio of 5 (MGO-5) exhibited a better catalytic efficiency and could be effectively reused four times. The influences of the pollutant, catalyst, and oxidant concentrations were investigated, and the intrinsic relationships among these factors and the degradation kinetic constant were evaluated by a fitting method. It was found that the catalytic degradation process in the MGO-5-persulfate-2,4-DCP system was most likely dominated by an interfacial catalytic reaction, with an activation energy of 13.88 kJ/mol. Radical quenching experiments and electron paramagnetic resonance (EPR) analysis indicated that both sulfate radicals (SO₄^-) and hydroxyl radicals (OH) were responsible for 2,4-DCP removal, but surface-bounded SO₄^- played a greater role. Chloride ions at a concentration of 0-60 mg/L had no effect on 2,4-DCP removal. The proposed advanced oxidation technology has potential applications for the practical removal of aqueous organic pollutants.

Degradation of 2,4-dichlorophenol by CuO-activated peroxydisulfate: Importance of surface-bound radicals and reaction kinetics

Peroxydisulfate (PDS, S₂O₈^2-) is a promising oxidant for water treatment and contaminated groundwater remediation. It requires activation to generate sulfate radical (SO₄^-) and hydroxyl radical (OH) for indirect oxidation of organic pollutants. Recently, efforts were devoted to developing PDS activation systems for direct oxidation of organic pollutants without producing radicals. However, the mechanism was still ambiguous and the kinetics was either not quantified or empirical in nature. In this research, we examined the activation of PDS by CuO for the degradation of 2,4-dichlorophenol (2,4-DCP). Dual-compound control experiments, radical scavenging tests and electron paramagnetic resonance (EPR) studies showed that surface-bound OH generated from the adsorbed PDS was the main reactive species responsible for the degradation of 2,4-DCP. A kinetic model considering the important reaction steps, including the adsorption of PDS onto CuO, activation of adsorbed PDS to form surface-bound SO₄^- and then surface-bound OH, and degradation of 2,4-DCP by surface-bound OH, was developed to better elucidate the reaction kinetics. The results suggested that the overall reaction kinetics of 2,4-DCP degradation was regulated by the adsorption of PDS onto CuO and the electron transfer between surface Cu and adsorbed PDS to form surface-bound SO₄^-. The developed kinetic model could serve as a framework to characterize other persulfate oxidation systems relying on surface-bound radicals.

The impact of wastewater matrix on the degradation of pharmaceutically active compounds by oxidation processes including ultraviolet radiation and sulfate radicals

Ultraviolet radiation (UV)-activated peroxydisulfate (PDS) and peroxymonosulfate (PMS) advanced oxidation processes were examined for their capacity to remove nine pharmaceutically active compounds (PhACs) from secondary effluent. The effect of operational parameters (initial oxidant concentration, UV exposure time, pH, common coexisting anions and effluent organic matter (EfOM)) on UV/PDS and UV/PMS treatment efficiency was investigated in a collimated beam device housing a low-pressure mercury UV lamp emitting light at 253.7 nm. Both AOPs achieved high removals (>90%) when applied to pure water. Under otherwise similar conditions the removal percentage fell by 20-30% due to the scavenging of effluent organic matter (EfOM) in secondary effluent. Finally, eliminating EfOM but maintaining the inorganic composition, the radical scavenging effect was reduced and 98.3% and 85.6% average removals were obtained by UV/PDS and UV/PMS, respectively. Increasing pH improved degradation of several PhACs containing amine groups. Higher oxidant dosages created only a significant benefit in UV/PDS. The chloride anion produced a negligible effect on both processes, while higher nitrate concentrations increased removal percentage but did not affect degradation rate constants. Finally and surprisingly, the addition of bicarbonate had the strongest positive impact on the degradation kinetics observed, even stronger than the elimination of EfOM from secondary effluent.

Comparison of UV/Persulfate and UV/H2O2 for the removal of naphthenic acids and acute toxicity towards Vibrio fischeri from petroleum production process water

The ultraviolet light-activated persulfate process (UV/Persulfate) has received much attention in recent years as a novel advanced oxidation method for the treatment of municipal and industrial wastewater. This work investigated the UV/Persulfate and UV/H₂O₂ processes for the treatment of real oil sands process water (OSPW) at ambient pH condition using a medium pressure mercury lamp (emission between 200 and 530 nm). The degradation performances towards fluorophore organic compounds and naphthenic acids (NAs) in OSPW were evaluated using synchronous fluorescence spectrometry and ultra performance liquid chromatography time-of-flight mass spectrometry, respectively. Compared to the UV/H₂O₂ process, the UV/Persulfate process exhibited higher efficiency to remove both NAs and fluorophore organic compounds. Under 40 min of UV exposure and incident irradiance of 3.50 mW cm^-2, fluorophore organic compounds were greatly degraded by UV/Persulfate (2 mM) and two- and three-ring fused organics were completely removed. 59.4%, 83.8% and 92.2% of O₂-NAs in OSPW were removed with persulfate dosages of 0.5, 2, and 4 mM, respectively. The removal efficiency decreased along with the number of oxygen atoms in NAs (83.8%, 49.3%, and 46.8% for O₂-, O₃-, and O₄-NAs, respectively) with 2 mM of persulfate, because of the formation of oxidized NAs in the same process. The structure-reactivity of O₂-NA compounds fitted pseudo-first order kinetics in UV/Persulfate process with the rate constants ranging from 0.0156 min^-1 to 0.1511 min^-1. NAs with higher carbon numbers and double bond equivalence were more reactive in the UV/Persulfate oxidation process. The acute toxicity of OSPW to Vibrio fischeri was significantly reduced after the UV/Persulfate and UV/H₂O₂ treatments. Overall results demonstrated that the UV/Persulfate oxidation can be an effective alternative for future reclamation of OSPW.

Improved degradation of anthraquinone dye by electrochemical activation of PDS

Electrochemical oxidation (EO) coupled with peroxydisulfate (PDS) activation as a synergistic wastewater treatment process (PDS/EO) was performed to degrade anthraquinone dye-Reactive Brilliant Blue (RBB) in aqueous solution. Introducing PDS into the EO improved the RBB removal than the sole PDS and conventional EO systems. The RBB could activate PDS to a certain degree by itself. By the comparison of various inorganic ions addition, it showed that adding NO₃^- as the background electrolyte was more effective than the systems using the Cl^- and SO₄^2-, respectively. In this PDS/EO-NO₃^- system, increasing PDS concentration (1-5 mmol L^-1) and current density (5-10 mA cm^-2) considerably promoted the degradation of RBB. The adjustment of the solution pH displayed that the acidic and neutral condition was beneficial to the RBB removal, and the synergistic effect was inverse ratio to the RBB initial concentration. Furthermore, the scavenger experiments verified that both SO₄^·- and HO· were the major active substances in the RBB decomposition, and other reactive oxygen species also had considerable contributions. Thereinto NO₃^- only act a catalytic agent to improve the generation of active matters in the PDS/EO-NO₃^-. Overall, the proposed synergistic process could serve as an efficient method for the degradation of anthraquinone dye.

Evaluation of transformation products from chemical oxidation of micropollutants in wastewater by photoassisted generation of sulfate radicals

In this research, the degradation of seven different micropollutants (MPs) and the formation of their transformation products (TPs) have been assessed during the application of different advanced oxidation processes: photolytic and photocatalytic activation of peroxymonosulfate (PMS) and persulfate (PS). The results were compared with those obtained from the photolytic experiments using hydrogen peroxide (H₂O₂) as oxidant. A significant abatement of almost all MPs was achieved, even with very low UV-C contact time (9 and 28 s). The degradation of atenolol (ATN) and caffeine (CFN) ranged from 84 to 100% with a dose of 0.5 mM of any oxidant. The efficiencies for bisphenol-A (BPA), carbamazepine (CBZ), diclofenac (DCF), ibuprofen (IBP), and sulfamethoxazole (SMX) varied depending on the oxidation system and operating conditions (oxidant dose and UV-C contact time), leading to the photolysis of PMS to higher efficiencies than PS and H₂O₂. In all cases, the abatement of MPs ranged from 63 to 83%, even with the lowest PMS dosage. Moreover, the addition of Fe(II) as a catalyst enhanced the removal efficiency, reaching almost total removal, especially over CBZ, DCF, and IBP. The Dissolved Organic Carbon (DOC) removal ranged between 44 and 62%, suggesting the transformation of MPs in intermediate compounds. The identification of transformation products was carried out for each micropollutant and each oxidation treatment, being observed some transformation products specific of oxidation by sulfate radicals. For example, m/z 165.0432 only appeared after PMS/Fe(II)/UV-C on the degradation of BFA, m/z 251.082 appeared after photolytic activation of PMS and PS on CBZ removal, and m/z 128.0452 was observed after any sulfate radical oxidation treatment, but not after photolysis of H₂O₂.

Degradation of antibiotics by modified vacuum-UV based processes: Mechanistic consequences of H2O2 and K2S2O8 in the presence of halide ions

In this work, the degradation of cefalexin, norfloxacin, and ofloxacin was examined via various advanced oxidation processes (AOPs). Direct photolysis by ultraviolet (UV) and vacuum ultra violet (VUV) was less effective for the degradation of fluoroquinolone antibiotics such as norfloxacin and ofloxacin than that of cefalexin. Both hydrogen peroxide (H₂O₂) and potassium persulfate (K₂S₂O₈) assisted UV/VUV process remarkably enhanced fluoroquinolone degradation. The addition of K₂S₂O₈ was superior to H₂O₂ under VUV irradiation, with the best removal efficiency of norfloxacin and ofloxacin being almost 100% within 3 min in the presence of VUV/K₂S₂O₈. The ofloxacin degradation rate was accelerated as concentrations of H₂O₂ and K₂S₂O₈ was increased to 3 mM, but the degradation rate was slightly decreased with excess H₂O₂ (>3 mM). The performance of modified VUV processes (i.e., VUV/H₂O₂ and VUV/K₂S₂O₈) was inhibited at highly alkaline condition (pH 11). The co-existence of halides (Cl^- and Br^-) enhanced antibiotics degradation via the modified VUV processes, but the reaction was almost unaffected in the presence of single halides. This study demonstrated that modified VUV processes (especially VUV/K₂S₂O₈) are efficient for eliminating fluoroquinolone antibiotics from water, which can be considered as a clean and green method for the treatment of antibiotics-containing industrial wastewater.

Reclamation of agro-wastewater polluted with pesticide residues using sunlight activated persulfate for agricultural reuse

The removal of 17 pesticides (pymetrozine, flonicamid, imidacloprid, acetamiprid, cymoxanil, thiachloprid, spinosad, chlorantraniliprole, triadimenol, tebuconazole, fluopyram, difenoconazole, cyflufenamid, hexythiazox, spiromesifen, folpet and acrinathrin) found in agro-wastewater from washing of containers and phytosanitary treatments equipment, has been carried out using sodium persulfate (Na₂S₂O₈) at pilot plant scale under natural sunlight. Persulfate is a strong oxidant, inexpensive and environmentally appropriate. However, this oxidant is slow in kinetics under ordinary conditions. Na₂S₂O₈ can be activated by ultraviolet light, generating SO₄^- radicals, which are also a very strong oxidizing species (E₀ = 2.6 V). Previously, preliminary experiments were carried out at laboratory scale using a photoreactor to optimize the Na₂S₂O₈ (300 mg L^-1) concentration on the rate constants of the found pesticides. The residual levels of the studied pesticides in agro-wastewater (900 L) were in the range 0.02-1.17 mg L^-1 for acrinathrin and fluopyram, respectively. After treatment, nearly complete degradation (>97%) of the parent molecules was achieved although 13% of initial DOC was measured. No significant differences (p < 0.05) were found when comparing grown broccoli using reclaimed and unreclaimed water.

Assessment of full-scale tertiary wastewater treatment by UV-C based-AOPs: Removal or persistence of antibiotics and antibiotic resistance genes?

This research reports for the first time the full-scale application of different homogeneous Advanced Oxidation Processes (AOPs) (H₂O₂/UV-C, PMS/UV-C and PMS/Fe(II)/UV-C) for the removal of antibiotics (ABs) and antibiotic resistance genes (ARGs) from wastewater effluent at Estiviel wastewater treatment plant (WWTP) (Toledo, Spain). AOPs based on the photolytic decomposition of H₂O₂ and peroxymonosulfate tested at low dosages (0.05-0.5 mM) and with very low UV-C contact time (4-18 s) demonstrated to be more efficient than UV-C radiation alone on the removal of the analyzed ABs. PMS (0.5 mM) combined with UV-C (7 s contact time) was the most efficient treatment in terms of AB removal: 7 out of 10 ABs detected in the wastewater were removed more efficiently than using the other oxidants. In terms of ARGs removal efficiency, UV-C alone seemed the most efficient treatment, although H₂O₂/UV-C, PMS/UV-C and PMS/Fe(II)/UV-C were supposed to generate higher concentrations of free radicals. The results show that treatments with the highest removal of ABs and ARGs did not coincide, which could be attributed to the competition between DNA and oxidants in the absorption of UV photons, reducing the direct photolysis of the DNA. Whereas the photolytic ABs removal is improved by the generation of hydroxyl and sulfate radicals, the opposite behavior occurs in the case of ARGs. These results suggest that a compromise between ABs and ARGs removal must be achieved in order to optimize wastewater treatment processes.

Enhanced removal of organic contaminants in water by the combination of peroxymonosulfate and carbonate

In this study, a favorable CO₃^2-/PMS system for efficient degradation of organic contaminants (acid orange 7 (AO7), acetaminophen, para-aminobenzoic acid, phenol, methylene orange, methylene blue) in water was firstly reported. Under optimal conditions, the decolorization ration of AO7 was 100% within 40 min. Data fitting showed that the AO7 decolorization could be described by the pseudo-first-order kinetics, and the rates constant values ranging from 0.0006 to 0.2297 min^-1 depending on the operating parameters (initial PMS, CO₃^2-, AO7 concentrations). Radical scavenging studies revealed that superoxide anion radical (O₂^-) and singlet oxygen (¹O₂) rather than sulfate (SO₄^-) nor hydroxyl (HO) were the dominant oxidants might be responsible for AO7 degradation. The presence of NO₃^-, HPO₄^2- and low concentration of Cl^-, NO₂^-, HCO₃^-, H₂PO₄^-, HA had no significantly effect on the decolorization of AO7. Adding a higher Cl^- concentration displayed favorable effects on the removal efficiencies of AO7, but adding a higher NO₂^-, HCO₃^-, H₂PO₄^- and HA concentration apparently inhibited this process. The decolorization of AO7 was lower in wastewater in comparison to other natural waters and ultrapure water, which was probably due to the presence of higher concentration of colloids in wastewater. Nevertheless, up to 94.8%, 97.0% and 85.1% of AO7 were degraded from the filtrate, permeate, and retentate phases of wastewater within 60 min, respectively. Consequently, CO₃^2-/PMS would be promising for removal methodology for AO7 in wastewater containing considerable colloids. Finally, three intermediates were identified and degradation pathways of AO7 were proposed.

Assessment of Sulfate Radical-Based Advanced Oxidation Processes for Water and Wastewater Treatment: A Review

High oxidation potential as well as other advantages over other tertiary wastewater treatments have led in recent years to a focus on the development of advanced oxidation processes based on sulfate radicals (SR-AOPs). These radicals can be generated from peroxymonosulfate (PMS) and persulfate (PS) through various activation methods such as catalytic, radiation or thermal activation. This review manuscript aims to provide a state-of-the-art overview of the different methods for PS and PMS activaton, as well as the different applications of this technology in the field of water and wastewater treatment. Although its most widespread application is the elimination of micropollutants, its use for the disinfection of wastewater is gaining increasing interest. In addition, the possibility of combining this technology with ultrafiltration membranes to improve the water quality and lifespan of the membranes has also been discussed. Finally, a brief economic analysis of this technology has been undertaken and the different attempts made to implement it at full-scale have been summarized. As a result, this review tries to be useful for all those people working in that area.

Removal of trace organic chemicals in wastewater effluent by UV/H2O2 and UV/PDS

In this study, we comparatively investigated the degradation of 12 trace organic chemicals (TOrCs) during UV/H₂O₂ and UV/peroxydisulfate (PDS) processes. Second-order rate constants for the reactions of iopromide, phenytoin, caffeine, benzotriazole, and primidone with sulfate radical (SO₄^•-) were determined for the first time. Experiments were conducted in buffered pure water and wastewater effluent with spiked TOrCs. UV/PDS degraded all TOrCs more efficiently than UV/H₂O₂ in buffered pure water due to the higher yield of SO₄^•- than that of hydroxyl radical (^•OH) at the same initial molar dose of PDS and H₂O₂, respectively. UV/PDS showed higher selectivity toward TOrCs removal than UV/H₂O₂ in wastewater effluent. Compounds with electron-rich moieties, such as diclofenac, venlafaxine, and metoprolol, were eliminated faster in UV/PDS whereas UV/H₂O₂ was more efficient in degrading compounds with lower reactivity to SO₄^•-. The fluence-based rate constants ( [Formula: see text] ) of TOrCs in wastewater effluent linearly increased as a function of initial H₂O₂ dose during UV/H₂O₂, possibly due to the constant scavenging impact of the wastewater matrix on ^•OH. However, exponential increase of k_obs-UV/PDS with increasing PDS dose was observed for most compounds during UV/PDS, suggesting the decreasing scavenging effect of the water matrix (electron-rich site of effluent organic matter (EfOM)) after initial depletion of SO₄^•- at low PDS dose. Fulvic and humic-like fluorophores appeared to be more persistent during UV/H₂O₂ compared to aromatic protein and soluble microbial product-like fluorophores. In contrast, UV/PDS efficiently degraded all identified fluorophores and showed less selectivity toward the fluorescent EfOM components. Removal pattern of TOrCs during pilot-scale UV/PDS was consistent with lab-scale experiments, however, overall removal rates were lower due to the presence of higher concentration of EfOM and nitrite.