Cost comparison of advanced oxidation processes for wastewater treatment using accumulated oxygen-equivalent criteria

Efficient removal of succinic acid by continuous hydrodynamic cavitation combined with ozone and side influent injection

Micropollutants (MPs) encompass a range of human-made pollutants present in trace amounts in environmental systems. MPs include pharmaceuticals, personal care products, pesticides, persistent organic pollutants, micro- and nano-plastics, and artificial sweeteners, all posing ecological risks. Conventional municipal wastewater treatment methods often face challenges in completely removing MPs due to their chemical characteristics, stability, and resistance to biodegradation. In this research, an Advanced Oxidation Process, combining hydrodynamic cavitation (HC) with dissolved ozone (O3) and side injection, was employed to efficiently degrade succinic acid (SA), an ozone-resistant compound and common byproduct. The HC/O3 process was run to treat different synthetic effluents, focusing on evaluating the influence of O3-to-total organic carbon (TOC) ratio, cavitation number (Cv) and O3 dosage. Notably, the results from a series of 14 experiments highlighted the critical significance of a low O3-to-TOC ratio value of 0.08 mg/mg and Cv value of 0.056 in HC for achieving efficient SA removal of 41.2% from an initial SA solution (106.3 mg/L). Regarding a series of four proof-of-concept experiments and their replications, the average TOC removal reached 62% when treating wastewater treatment plant effluent spiked with SA. This significant removal rate was achieved under initial conditions: Cv of 0.02, O3-to-TOC ratio set at 0.77 mg/mg, TOC concentration of 47.7 mg/L, 106 mg/L of SA, and a temperature of 25 °C. Notably, the electrical energy per order required for the 62% reduction in TOC was a modest 12.5 kWh/m3/order, indicating the potential of the continuous HC/O3 process as a promising approach for degrading a wide range of MPs.

The recent development of innovative photoelectro-Fenton processes for the effective and cost-effective remediation of organic pollutants in waters

Wastewaters with toxic and recalcitrant organic contaminants are poorly remediated in conventional wastewater treatment plants. So, powerful processes need to be developed to destroy such organic pollutants to preserve the quality of the aquatic environment. This critical and comprehensive review presents the recent innovative development of photoelectro-Fenton (PEF) covering the period 2019-September 2024. This emerging photo-assisted Fenton-based electrochemical advanced oxidation process (EAOP) is an efficient and cost-effective treatment for water remediation. It possesses a great oxidation power because the in-situ generated hydroxyl radical as oxidant is combined with the photolysis of the organic by-products under UV or sunlight irradiation. The review is initiated by a brief description of the characteristics of the PEF process to stand out in the role of generated oxidizing agents. Further, the homogeneous PEF. PEF-like, solar PEF (SPEF), and SPEF-like processes with iron catalysts are discussed, taking examples of their application to the removal and mineralization of solutions of industrial chemicals, herbicides, dyes, pharmaceuticals, and direct real wastewaters. Novel heterogeneous PEF treatments of such pollutants with solid iron catalysts or functionalized cathodes are analyzed. Finally, novel hybrid processes including PEF/photocatalysis and PEF/photoelectrocatalysis, followed by novel and potent sequential processes like electrocoagulation-PEF and persulfate-PEF, are discussed. Throughout the manuscript, special attention was made to the total operating cost of PEF, which is more expensive than conventional electro-Fenton due to the high electric cost of the UV lamp, pointing to consider the much more cost-effective SPEF as a preferable alternative in practice.

Hydrogen bond-induced supramolecular self-assembly strategy to fabricate ultra-dispersed Cu-loaded porous tubular graphitic carbon nitride with rich nitrogen vacancies and CuNx sites for efficient photo-Fenton catalysis

The low utilization of visible light and easy recombination of charge carriers of graphitic carbon nitride (CN) restrain its application as photo-electron donor and metal site support in photo-Fenton system. Herein, a hydrogen bond-induced supramolecular self-assembly strategy was created to fabricate an ultra-dispersed Cu-loaded porous tubular CN composite (CA-Cu/TCN) by the hydrothermal-pyrolysis method with citric acid (CA) as initiator and chelating agent. CA-Cu/TCN with rich nitrogen vacancies (NVs) and abundant ultra-dispersed CuNx sites exhibited narrow bandgap, favorable visible light absorption capability, and high separation and transfer efficiency of charge carriers. CA-Cu/TCN effectively catalyzed the activation of H2O2 for generating abundant reactive oxygen species under visible light irradiation, contributing to efficient degradation of ciprofloxacin (CIP) with removal rate of 95.9 % and kinetic rate constant of 0.0948 min-1. The superior catalytic activity of CA-Cu/TCN can be ascribed to the effective transport of photogenerated electrons, high specific surface area, atomically dispersed Cu species, and enriched surface NVs. The mechanism of photo-Fenton catalytic degradation of CIP and possible degradation pathways were proposed as the dominant role of 1O2. Toxicity evaluation of CIP and intermediates indicated that the degradation of CIP was a gradual detoxification process. This work offers a novel self-assembly strategy to design and synthesize highly active and sustainable visible light-driven photo-Fenton catalysts for effectively degrading organic pollutants.

Challenges and opportunities for large-scale applications of the electro-Fenton process

As an electrochemical advanced oxidation process, the electro-Fenton (EF) process has gained significant importance in the treatment of wastewater and persistent organic pollutants in recent years. As recently reported in a bibliometric analysis, the number of scientific publications on EF have increased exponentially since 2002, reaching nearly 500 articles published in 2022 (Deng et al., 2022). The influence of the main operating parameters has been thoroughly investigated for optimization purposes, such as type of electrode materials, reactor design, current density, and type and concentration of catalyst. Even though most of the studies have been conducted at a laboratory scale, focusing on fundamental aspects and their applications to degrade specific pollutants and treat real wastewater, important large-scale attempts have also been made. This review presents and discusses the most recent advances of the EF process with special emphasis on the aspects more closely related to future implementations at the large scale, such as applications to treat real effluents (industrial and municipal wastewaters) and soil remediation, development of large-scale reactors, costs and effectiveness evaluation, and life cycle assessment. Opportunities and perspectives related to the heterogeneous EF process for real applications are also discussed. This review article aims to be a critical and exhaustive overview of the most recent developments for large-scale applications, which seeks to arouse the interest of a large scientific community and boost the development of EF systems in real environments.

Heavy metals removal by algae and usage of activated metal-enriched biomass as cathode catalyst for improving performance of photosynthetic microbial fuel cell

Cytotoxic, malignant, and mutagenic pollutants like heavy metals have emerged as a serious global threat to the ecosystem. Additionally, the quantity of noxious metals in water bodies has increased due to expanding industrial activities and the application of incompetent wastewater treatment techniques. Owing to the benefits of eco-friendly phytoremediation, the utilization of algae in photosynthetic microbial fuel cell (PMFC) for removal of heavy metals has attracted increasing attention among researchers. Therefore, a successful fabrication and operation of a modular PMFC for simultaneous algal biomass production was exhibited, thus resulting in significant removal efficiency of Cu(II) (94 %) and Co(II) (88 %). Moreover, Co(II)-accumulated algal biochar after thermal activation was utilized as a cathode catalyst for the first time and attained 64.2 mW/m2 of power density through PMFC. Hence, this easily synthesised green cathode catalyst proved its ability to enhance the overall performance of PMFC by attaining higher power output while treating wastewater.

Model-based development of cell voltage control system for modified bio-electro-Fenton process

A modified bio-electro-Fenton (M-BEF) process with a cell voltage control system that improves the efficiency of organic removal and energy savings is demonstrated. The M-BEF process can accomplish bioelectricity generation, H2O2 production, and the Fenton reaction in a continuous-flow reactor. During synthetic wastewater treatment containing biodegradable (glucose) and recalcitrant (biphenyl) organic matter, the effluent chemical oxygen demand (COD) concentration was maintained between 2 and 6 mg L-1. To investigate the impact of different operating schemes on energy usage, model-based design (MBD) modeling and simulations were performed, which showed that COD removal efficiency without an external voltage supply was unstable at < 70 %. The automatic cell voltage control system saved 90 % of the power compared to the continuous cell voltage supply system. Further testing on more environmental samples and pollutants will enable real-time optimization of supplied power and wastewater treatment using the cell voltage control system.

Integrating electro-Fenton and microalgae for the sustainable management of real food processing wastewater

The present study demonstrates, for the first time, the feasibility of a two-step process consisting of Electro-Fenton (EF) followed by microalgae to treat highly loaded real food processing wastewater along with resource recovery. In the first step, EF with a carbon felt cathode and Ti/RuO2-IrO2 anode was applied at different current densities (3.16 mA cm-2, 4.74 mA cm-2 and 6.32 mA cm-2) to decrease the amount of organic matter and turbidity and enhance biodegradability. In the second step, the EF effluents were submitted to microalgal treatment for 15 days using a mixed culture dominated by Scenedesmus sp., Chlorosarcinopsis sp., and Coelastrum sp. Results showed that current density impacted the amount of COD removed by EF, achieving the highest COD removal of 77.5% at 6.32 mA cm-2 with >95% and 74.3% of TSS and PO43- removal, respectively. With respect to microalgae, the highest COD removal of 85% was obtained by the culture in the EF effluent treated at 6.32 mA cm-2. Remarkably, not only 85% of the remaining organic matter was removed by microalgae, but also the totality of inorganic N and P compounds, as well as 65% of the Fe catalyst that was left after EF. The removal of inorganic species also demonstrates the high complementarity of both processes, since EF does not have the capacity to remove such compounds, while microalgae do not grow in the raw wastewater. Furthermore, a maximum of 0.8 g L-1 of biomass was produced after cultivation, with an accumulation of 32.2% of carbohydrates and 25.9% of lipids. The implementation of the two processes represents a promising sustainable approach for the management of industrial effluents, incorporating EF in a water and nutrient recycling system to produce biomass that could be valorized into clean fuels.

Catalytic and biocatalytic degradation of microplastics

In recent years, there has been a surge in annual plastic production, which has contributed to growing environmental challenges, particularly in the form of microplastics. Effective management of plastic and microplastic waste has become a critical concern, necessitating innovative strategies to address its impact on ecosystems and human health. In this context, catalytic degradation of microplastics emerges as a pivotal approach that holds significant promise for mitigating the persistent effects of plastic pollution. In this article, we critically explored the current state of catalytic degradation of microplastics and discussed the definition of degradation, characterization methods for degradation products, and the criteria for standard sample preparation. Moreover, the significance and effectiveness of various catalytic entities, including enzymes, transition metal ions (for the Fenton reaction), nanozymes, and microorganisms are summarized. Finally, a few key issues and future perspectives regarding the catalytic degradation of microplastics are proposed.

Cyanide-Isolated Cobalt Catalyst for Ultraefficient Advanced Oxidation Treatment

Catalyst design with a "Co-N-C" structure at the atomic level has shown great interest for peroxymonosulfate (PMS) activation toward advanced oxidation water treatment. Here, we present an innovative way of producing cobalt hexacyanocobaltate (Co-HCC) with an abundance of atomically isolated CoII-NC sites at the outer surface. This material allows ultraefficient PMS activation to generate plenty of sulfate and hydroxyl radicals, with a turnover frequency much higher than those of most cobalt-based catalysts reported so far and even the homogeneous catalysis by Co2+ ions. We gained fundamental insights on its unprecedently high catalytic performance based on experimental results and computational study. Then, we controlled the growth of Co-HCC on a ceramic membrane to form a confined oxidation environment that utilizes the extended surface area and maximal exposure of short-lived radicals for a fast removal of organic pollutants that enter the pores. As a result, this catalytic membrane achieves complete disruption of micropollutants under a water flux up to 10,000 LMH (merely 0.2 s retention time) and further >90% mineralization of organic pollutants in complex industrial wastewater matrices (<100 s retention time), together with the merits of operational simplicity and great longevity (2 weeks continuous run). Our study elicits a new milestone in "Co-N-C" catalyst structure design for PMS activation and highlights the great interest of producing catalytic membranes for a confined treatment of organic pollutants from partial oxidation to complete mineralization as a new benchmark.

Efficient Photocatalytic Luminous Textile for Simulated Real Water Purification: Advancing Economical and Compact Reactors

The growing worldwide problem of wastewater management needs sustainable methods for conserving water supplies while addressing environmental and economic considerations. With the depletion of freshwater supplies, wastewater treatment has become critical. An effective solution is needed to efficiently treat the organic contaminants departing from wastewater treatment plants (WWTPs). Photocatalysis appears to be a viable method for eliminating these recalcitrant micropollutants. This study is focused on the degradation of Reactive Black 5 (RB5), a typical contaminant from textile waste, using a photocatalytic method. Titanium dioxide (TiO2) was deposited on a novel luminous fabric and illuminated using a light-emitting diode (LED). The pollutant degrading efficiency was evaluated for two different light sources: (i) a UV lamp as an external light source and (ii) a cold LED. Interestingly, the LED UV source design showed more promising results after thorough testing at various light levels. In fact, we note a 50% increase in mineralization rate when we triple the number of luminous tissues in the same volume of reactor, which showed a clear improvement with an increase in compactness.

Microplastic removal and management strategies for wastewater treatment plants

Discharging microplastics into the environment with treated wastewater is becoming a major concern around the world. Wastewater treatment plants (WWTPs) release microplastics into terrestrial and aquatic habitats, mostly from textile, laundry, and cosmetic industries. Despite extensive research on microplastics in the environment, their removal, and WWTP management strategies, highlighting their environmental effects, little is known about microplastics' fate and behaviour during various treatment processes. Microplastics interact with treatment technologies differently due to their diverse physical and chemical characteristics, resulting in varying removal efficiency. Microplastics removed from WWTPs may accumulate in soil and harm terrestrial ecosystems. Few studies have examined the cost, energy use, and trade-offs of large-scale implementation of modern treatment methods for the removal of microplastics. To safeguard aquatic and terrestrial habitats from microplastics' contamination, focused and efficient management techniques must bridge these knowledge gaps. This review summarizes microplastic detection, collection, removal and management strategies. A compilation of treatment process studies on microplastics' removal efficiency and their destiny and transit paths shows recent improvement. Bioremediation, membrane bioreactor (MBR), electrocoagulation, sol-gel technique, flotation, enhanced filtering, and AOPs are evaluated for microplastic removal. The fate and behaviour of microplastics in WWTPs suggest they may be secondary suppliers of microplastics to receiving ecosystems. Innovative microplastic removal strategies and technologies such as nanoparticles, microorganism-based remediation, and tertiary treatment raise issues. These new WWTP technologies are examined for feasibility, limitations, and implementation issues. Pretreatment modifies microplastic size, adsorption potential, and surface morphology to remove microplastics from WWTPs. Membrane bioreactors (MBR) can remove 99.9% of microplastics more efficiently than other approaches. MBR systems require membrane cleaning and fouling control, which raises operational and capital costs. To reduce MPs, plastic alternatives and strict controls, including microplastic waste transformation, should be prioritized. Microplastics must be controlled through monitoring policy execution and awareness.

Scalability of advanced oxidation processes (AOPs) in industrial applications: A review

Disinfection and decontamination of water by application of oxidisers is an essential treatment step across numerous industrial sectors including potable supply and industry waste management, however, could be greatly enhanced if operated as advanced oxidation processes (AOPs). AOPs destroy contaminants including pathogens by uniquely harnessing radical chemistry. Despite AOPs offer great practical opportunities, no reviews to date have highlighted the critical AOP virtues that facilitate AOPs' scale up under growing industrial demand. Hence, this review analyses the critical AOP parameters such as oxidant conversion efficiency, batch mode vs continuous-flow systems, location of radical production, radical delivery by advanced micro-/mesoporous structures and AOP process costs to assist the translation of progressing developments of AOPs into their large-scale applications. Additionally, the state of the art is analysed for various AOP inducing radical/oxidiser measurement techniques and their half-lives with a view to identify radicals/oxidisers that are suitable for in-situ production. It is concluded that radicals with short half-lives such as hydroxyl (10-4 μsec) and sulfate (30-40 μsec) need to be produced in-situ via continuous-flow reactors for their effective transport and dosing. Meanwhile, radicals/oxidisers with longer half-lives such as ozone (7-10 min), hydrogen peroxide (stable for several hours), and hypochlorous acid (10 min -17 h) need to be applied through batch reactor systems due to their relatively longer stability during transportation and dosing. Complex and costly synthesis as well as cytotoxicity of many micro-/mesoporous structures limit their use in scaling up AOPs, particularly to immobilising and delivering the short-lived hydroxyl and sulfate radicals to their point of applications. Overall, radical delivery using safe and advanced biocompatible micro-/mesoporous structures, radical conversion efficiency using advanced reactor design and portability of AOPs are priority areas of development for scaling up to industry.

Recent advancements in peroxicoagulation process: An updated review

The present article describes the recent advancements (since 2018) in peroxicoagulation (PC) process, which was introduced by Professor Enric Brillas and his group in 1997. Instead of checking the efficiency of PC process to degrade a targeted pollutant in synthetic wastewater, researchers started testing its efficacy for the treatment of complex real wastewater. Applications like disinfection and removal of heavy metals as well as oxidative removal of arsenite from water were tested recently. To improve the efficiency of PC process, modifications were made for electrode materials (both anode and cathode) and electrolytic cells. Performance of PC process in combination with other treatment technologies is also discussed.

Influence of ozone microbubble enhanced oxidation on mine effluent mixes and Daphnia magna toxicity

The mining industry often must mix different kinds of water on the mine site during pre-treatment or post-treatment before the final discharge of the treated water to the environment. Microbubble ozonation has proven to be efficient in the removal of contaminants of concern from mine water, such as metals, metalloids, and nitrogen compounds, which can persist in the environment and entail toxicity issues. This study evaluated the efficiency of ozone microbubbles combined with lime precipitation on contaminant removal and its impact on toxicity for Daphnia magna with five different mine effluent mixes from an active mine site located in Abitibi-Témiscamingue, QC, Canada. For the non-acidic mixes, two scenarios were tested: first, pre-treatment of metals using lime precipitation and a flocculant was conducted prior to ozonation; and second, ozonation was conducted prior to metals post-treatment using the same precipitation and flocculation technique. Results showed that the NH₃-N removal efficiency ranged from 90% for the lower initial concentrations (1.1 mg/L) to more than 99% for the higher initial concentrations (58.4 mg/L). Moreover, ozonation without metals pre-treatment improved NH₃-N treatment efficiency in terms of kinetics but entailed abnormal toxicity issues. Results of bioassays conducted on water with metals pre-treatment did not show any toxicity events but showed abnormal toxicity patterns on the mixes treated without metals pre-treatment (diluted effluents were toxic, while undiluted were not). At 50% dilution, the water was toxic, probably due to the potential presence of metal oxide nanoparticles. The confirmation of the source of toxicity requires further investigation.

Efficient utilization of free radicals in advanced oxidation processes under high-gravity environment for disposing pollutants in effluents and gases: A critical review

Advanced oxidation processes (AOPs) using strongly oxidizing radicals are promising for wastewater treatment and gas purification. Nevertheless, the short half-life of radicals and the limited mass transfer in traditional reactors cause under-utilization of radicals and low pollutant removal efficiency. High-gravity technology (HiGee)-enhanced AOPs (HiGee-AOPs) have been demonstrated a promising way to enhance radical utilization in a rotating packed bed reactor (RPB). Here, we review the potential mechanisms of intensified radical utilization in HiGee-AOPs, structures and performance of RPB, and applications of HiGee in AOPs. The intensification mechanisms are described from three aspects: enhanced generation of radicals by efficient mass transfer, in-situ radical utilization under frequent liquid film renewal, and selective effect on radical utilization due to micromixing in RPB. Based on these mechanisms, we propose a novel High-gravity flow reaction with the essence of efficiency, in-situ, and selectivity in order to better explain the strengthening mechanisms in HiGee-AOPs. HiGee-AOPs possess great potential for treating effluent and gaseous pollutants due to characteristics of High-gravity flow reaction. We discuss the pros and cons of different RPBs and their applications to specific HiGee-AOPs. HiGee improve the following AOPs: (1) facilitate interfacial mass transfer in homogeneous AOPs, (2) enhance mass transfer to expose more catalytically active sites and mass-produce nanocatalysts for heterogeneous AOPs, (3) inhibit bubble accumulation on the electrode surface of electrochemical AOPs, (4) increase the mass transfer between liquid and catalysts in UV-assisted AOPs, (5) improve the micromixing efficiency of ultrasound-based AOPs. Strategies outlined in this paper should inspire further development of HiGee-AOPs.

Mechanistic and quantitative profiling of electro-Fenton process for wastewater treatment

Electro-Fenton (EF) process represents an energy-efficient and scalable advanced oxidation technology (AOT) for micropollutants removal in wastewaters. However, mechanistic profiling and quantitation of contribution of each subprocess (i.e., adsorption at electrode, coagulation, radical oxidation, electrode oxidation/reduction, and H₂O₂ oxidation) to the overall degradation are substantially unclear, resulting in difficulty in tunability and optimization for different treatment scenarios. In this study, we investigated degradation kinetics of a target micropollutant in an EF system. The contribution of all possible subprocesses was elucidated by comparing the observed degradation rate in the EF system with the sum of the kinetics in each subprocess. The results indicated that the overall degradation can be attributed to the synergistic action of the above-mentioned subprocesses. The radical oxidation accounts for 87% elimination, followed by electrode reoxidation/reduction of 7.7%. These results not only advance the fundamental understanding of synergistic effect in EF system, but also open new possibilities to optimize these techniques for better scalability. In addition, the methodology in this study could potentially boost the in-depth exploration of subprocess contribution in other Fenton-like systems.

Technical and economical assessment of the treatment of vinasse from Pisco production using the advanced oxidation process

The removal of organic matter from Pisco production wastewater was evaluated using coagulation/flocculation, filtration as a pre-treatment, and solar photo-Fenton, with the use of two types of photoreactors: compound parabolic collectors (CPC) and flat plate (FP), with and without utilizing the ozonation process. The overall removal efficiency for chemical oxygen demand (COD) was 63% and 15% using FP and CPC, respectively. Also, for the overall removal efficiency of polyphenols, a percentage of 73% and 43% were obtained using FP and CPC, respectively. When ozone was used in the solar photoreactors, the resulting trends were similar. COD and polyphenol removal, using an FP photoreactor in the solar photo-Fenton/O₃ process, resulted in values of 98.8% and 86.2% after the process. COD and polyphenol removal, using solar photo-Fenton/O₃ process in a CPC, resulted in values of 49.5% and 72.4%, respectively. The economic indicators of annual worth and economic treatment capacity established that FP reactors represent lower costs than CPCs. These results were corroborated by the economic analyses of the evolution of costs versus COD removed as well as by the cash flow diagrams projected for 5, 10, and 15 years.

Recent advances in the removal of emerging contaminants from water by novel molecularly imprinted materials in advanced oxidation processes-A review

Recently, there has been a global focus on effectively treating emerging contaminants (ECs) in water bodies. Advanced oxidation processes (AOPs) are the primary technology used for ECs removal. However, the low concentrations of ECs make it difficult to overcome the interference of background substances in complex water quality, which limits the practical application of AOPs. To address this limitation, many researchers are developing new catalysts with preferential adsorption. Molecular imprinting technology (MIT) combined with conventional catalysts has been found to effectively enhance the selectivity of catalysts for the targeted catalytic degradation of pollutants. This review presents a comprehensive summary of the progress made in research on molecularly imprinted polymers (MIPs) in the selective oxidation of ECs in water. The preparation methods, principles, and control points of novel MIP catalysts are discussed. Furthermore, the performance and mechanism of the catalysts in photocatalytic oxidation, electrocatalytic oxidation, and persulfate activation are analyzed with examples. The possible ecotoxicological risks of MIP catalysts are also discussed. Finally, the challenges and prospects of applying MIP catalysts in AOP are presented along with proposed solutions. This review provides a better understanding of using MIP catalysts in AOPs to target the degradation of ECs.

Recent advances in advanced oxidation processes (AOPs) for the treatment of nitro- and alkyl-phenolic compounds

The presence of phenolic compounds in the aquatic environment has posed severe risks due to their toxicity. Among the phenolic families, nitro- and alkyl-phenolic compounds have been categorized as precedence contaminants by the United States Environmental Protection Agency (US EPA). Therefore, efficient treatment methods for wastewater containing nitro- and alkyl-phenolic compounds are urgently needed. Due to the advantages of creating reactive species and generating efficient degradation of hazardous contaminants in wastewater, advanced oxidation processes (AOPs) are well-known in the field of treating toxic contaminants. In this review paper, the recent directions in AOPs, catalysts, mechanisms, and kinetics of AOPs are comprehensively reviewed. Furthermore, the conclusion summarizes the research findings, future prospects, and opportunities for this study. The main direction of AOPs lies on the optimization of catalyst and operating parameters, with industrial applications remain as the main challenge. This review article is expected to present a summary and in-depth understanding of AOPs development; and thus, inspiring scientists to accelerate the evolution of AOPs in industrial applications.

Techno-economic evaluation of UV light technologies in water remediation

Disinfection commonly follows conventional treatments in wastewater treatment and remediation plants aiming at reducing the presence of pathogens. However, the presence of the so called "micropollutants" has emerged as a serious concern, therefore developing tertiary treatments that are not only able to remove pathogens but also to degrade micropollutants is worth investigating. Nowadays, UV-C photo-degradation processes are widely used for disinfection due to their simplicity and easy operation; additionally, they have shown potential for the removal of contaminants of emerging concern. Conventional mercury lamps are being replaced by light-emitting diodes (LEDs) that avoid the use of toxic mercury and can be switched on and off with no effect on the lamp lifetime. This work aims to comparatively evaluate the performance of several photo-degradation technologies for the removal of two targeted micropollutants, the pharmaceutical dexamethasone (DXMT) and the herbicide S-metolachlor (MTLC), using UV irradiation doses typical of disinfection processes. To this end, the technical performance of UV-A/UV-C photolysis, UV-A/UV-C photocatalysis, UV-C/H₂O₂ and UV-C/NaOCl has been compared. The influence of operating conditions such as the initial concentration of the pollutants (3 mg L^-1 - 30 mg L^-1, concentrations found in membrane or adsorption remediation steps), pH (3-10), and water matrix (WWTP secondary effluent, and ultrapure water) on the degradation efficiency has been studied. The economic evaluation in terms of electricity and chemicals consumption and the carbon footprint has been evaluated. UV-C photolysis and UV-C photocatalysis appear as the most suitable technologies for the degradation of DXMT and MTLC, respectively, in terms of kinetics (1.53·10^-1 min^-1 for DXMT and 1.96·10^-2 min^-1 for MTLC), economic evaluation (1 € m^-3 for DXMT and 32 € m^-3 for MTLC) and environmental indicators (0.5 g-CO₂ for DXMT and 223.1 g-CO₂ for MTLC).

Treatment of sewage sludge hydrothermal carbonization aqueous phase by Fe(II)/CaO2 system: Oxidation behaviors and mechanism of organic compounds

The Fe(II)/CaO₂ system with a stable oxidant and a low-cost homogeneous activating agent has been considered as a prospective process for the disposal of wastewater. The system was constructed to treat sewage sludge hydrothermal carbonization aqueous phase (HTC-AP) in this study. As the hydrothermal temperature increased, the organics in the HTC-AP were first decomposed and then cyclized, while the Maillard reaction occurs throughout the stage. The oxidation efficiency of the Fe(II)/CaO₂ system was related to the composition of organics in HTC-AP, and the removal of dissolved organic carbon (DOC) by the system was 38.56 % in the HTC-AP obtained by hydrothermal treatment at 220 °C. Redundancy analysis showed that the low molecular weight organics, hydrophobic acids, and hydrophobic neutral components were beneficial to DOC removal, while Maillard products and cyclization products were hard to be oxidized to CO₂ and H₂O. The CN functional group of the protein facilitated DOC removal, and some organics in HTC-AP were oxidized to acids and phenols. The energy input to remove DOC in Fe(II)/CaO₂ system was 27.74 MJ per kg carbon. This study provides a low-energy consumption Fe(II)/CaO₂ system for the post-treatment of HTC-APs and explores the applicability of the system.

Evaluation of pathogen disinfection efficiency of electrochemical advanced oxidation to become a sustainable technology for water reuse

Water treatment and reuse is gaining acceptance as a strategy to fight against water contamination and scarcity, but it usually requires complex treatments to ensure safety. Consequently, the electrochemical advanced processes have emerged as an effective alternative for water remediation. The main objective here is to perform a systematic study that quantifies the efficiency of a laboratory-scale electrochemical system to inactivate bacteria, bacterial spores, protozoa, bacteriophages and viruses in synthetic water, as well as in urban wastewater once treated in a wetland for reuse in irrigation. A Ti|RuO₂-based plate and Si|BDD thin-film were comparatively employed as the anode, which was combined with a stainless-steel cathode in an undivided cell operating at 12 V. Despite the low resulting current density (<15 mA/cm²), both anodes demonstrated the production of oxidants in wetland effluent water. The disinfection efficiency was high for the bacteriophage MS2 (T99 in less than 7.1 min) and bacteria (T99 in about 30 min as maximum), but limited for CBV5 and TuV, spores and amoebas (T99 in more than 300 min). MS2 presented a rapid exponential inactivation regardless of the anode and bacteria showed similar sigmoidal curves, whereas human viruses, spores and amoebas resulted in linear profiles. Due the different sensitivity of microorganisms, different models must be considered to predict their inactivation kinetics. On this basis, it can be concluded that evaluating the viral inactivation from inactivation profiles determined for bacteria or some bacteriophages may be misleading. Therefore, neither bacteria nor bacteriophages are suitable models for the disinfection of water containing enteric viruses. The electrochemical treatment added as a final disinfection step enhances the inactivation of microorganisms, which could contribute to safe water reuse for irrigation. Considering the calculated low energy consumption, decentralized water treatment units powered by photovoltaic modules might be a near reality.

Degradation of the Selected Antibiotic in an Aqueous Solution by the Fenton Process: Kinetics, Products and Ecotoxicity

Sulfonamides used in veterinary medicine can be degraded via the Fenton processes. In the premise, the process should also remove the antimicrobial activity of wastewater containing antibiotics. The kinetics of sulfathiazole degradation and identification of the degradation products were investigated in the experiments. In addition, their toxicity against Vibrio fischeri, the MARA^® assay, and unselected microorganisms from a wastewater treatment plant and the river was evaluated. It was found that in the Fenton process, the sulfathiazole degradation was described by the following kinetic equation: r₀ = k C_STZ^{-1 or 0} C_Fe(II)³ C_H2O2^{0 or 1} C_TOC^-2, where r₀ is the initial reaction rate, k is the reaction rate constant, C is the concentration of sulfathiazole, Fe(II) ions, hydrogen peroxide and total organic carbon, respectively. The reaction efficiency and the useful pH range (up to pH 5) could be increased by UVa irradiation of the reaction mixture. Eighteen organic degradation products of sulfathiazole were detected and identified, and a possible degradation mechanism was proposed. An increase in the H₂O₂ dose, to obtain a high degree of mineralization of sulfonamide, resulted in an increase in the ecotoxicity of the post-reaction mixture.

Heterogeneous Catalytic Ozonation: Solution pH and Initial Concentration of Pollutants as Two Important Factors for the Removal of Micropollutants from Water

There are several publications on heterogeneous catalytic ozonation; however, their conclusions and the comparisons between them are not always consistent due to the variety of applied experimental conditions and the different solid materials used as catalysts. This review attempts to limit the major influencing factors in order to reach more vigorous conclusions. Particularly, it highlights two specific factors/parameters as the most important for the evaluation and comparison of heterogeneous catalytic ozonation processes, i.e., (1) the pH value of the solution and (2) the initial concentration of the (micro-)pollutants. Based on these, the role of Point of Zero Charge (PZC), which concerns the respective solid materials/catalysts in the decomposition of ozone towards the production of oxidative radicals, is highlighted. The discussed observations indicate that for the pH range 6–8 and when the initial organic pollutants’ concentrations are around 1 mg/L (or even lower, i.e., micropollutant), then heterogeneous catalytic ozonation follows a radical mechanism, whereas the applied solid materials show their highest catalytic activity under their neutral charge. Furthermore, carbons are considered as a rather controversial group of catalysts for this process due to their possible instability under intense ozone oxidizing conditions.

A detailed review on advanced oxidation process in treatment of wastewater: Mechanism, challenges and future outlook

The presence of several contaminants in waterbodies raises global pollution and creates major risks to mankind, wildlife, as well as other living organisms. Development of an effective, feasible, cost-effective and eco-friendly approach for treating wastewater that is discharged from various industries is important for bringing down the deposition of contaminants into environment. Advanced oxidation process is an efficient technique for treating wastewater owing to its advantages such as high oxidation efficacy and does not produce any secondary pollutants. Advanced oxidation process can be performed through various methods such as ozone, Fenton, electrochemical, photolysis, sonolysis, etc. These methods have been widely utilized for degradation of emerging pollutants that cannot be destroyed using conventional approaches. This review focuses on wastewater treatment using advanced oxidation process. A brief discussion on mechanism involved is provided. In addition, various types of advanced oxidation process and their mechanism are explained in detail. Challenges faced during wastewater treatment process using oxidation, electrochemical, Fenton, photocatalysis and sonolysis are discussed elaborately. Advanced oxidation process can be viewed as potential approach for treating wastewater with certain modifications and solving challenges.

Romo AI, Pudar S, Putnam ST, Bustos E, Rodríguez-López J. Real-Time Detection of Hydroxyl Radical Generated at Operating Electrodes via Redox-Active Adduct Formation Using Scanning Electrochemical Microscopy

The hydroxyl radical (•OH) is one of the most attractive reactive oxygen species due to its high oxidation power and its clean (photo)(electro)generation from water, leaving no residues and creating new prospects for efficient wastewater treatment and electrosynthesis. Unfortunately, in situ detection of •OH is challenging due to its short lifetime (few ns). Using lifetime-extending spin traps, such as 5,5-dimethyl-1-pyrroline N-oxide (DMPO) to generate the [DMPO-OH]• adduct in combination with electron spin resonance (ESR), allows unambiguous determination of its presence in solution. However, this method is cumbersome and lacks the necessary sensitivity and versatility to explore and quantify •OH generation dynamics at electrode surfaces in real time. Here, we identify that [DMPO-OH]• is redox-active with E0 = 0.85 V vs Ag|AgCl and can be conveniently detected on Au and C ultramicroelectrodes. Using scanning electrochemical microscopy (SECM), a four-electrode technique capable of collecting the freshly generated [DMPO-OH]• from near the electrode surface, we detected its generation in real time from operating electrodes. We also generated images of [DMPO-OH]• production and estimated and compared its generation efficiency at various electrodes (boron-doped diamond, tin oxide, titanium foil, glassy carbon, platinum, and lead oxide). Density functional calculations, ESR measurements, and bulk calibration using the Fenton reaction helped us unambiguously identify [DMPO-OH]• as the source of redox activity. We hope these findings will encourage the rapid, inexpensive, and quantitative detection of •OH for conducting informed explorations of its role in mediated oxidation processes at electrode surfaces for energy, environmental, and synthetic applications.

SARS-CoV-2 pharmaceutical drugs: a critical review on the environmental impacts, chemical characteristics, and behavior of advanced oxidation processes in water

This review summarizes research data on the pharmaceutical drugs used to treat the novel SARS-CoV-2 virus, their characteristics, environmental impacts, and the advanced oxidation processes (AOP) applied to remove them. A literature survey was conducted using the electronic databases Science Direct, Scopus, Taylor & Francis, Google Scholar, PubMed, and Springer. This complete research includes and discusses relevant studies that involve the introduction, pharmaceutical drugs used in the SARS-CoV-2 pandemic: chemical characteristics and environmental impact, advanced oxidation process (AOP), future trends and discussion, and conclusions. The results show a full approach in the versatility of AOPs as a promising solution to minimize the environmental impact associated with these compounds by the fact that they offer different ways for hydroxyl radical production. Moreover, this article focuses on introducing the fundamentals of each AOP, the main parameters involved, and the concomitance with other sources and modifications over the years. Photocatalysis, sonochemical technologies, electro-oxidation, photolysis, Fenton reaction, ozone, and sulfate radical AOP have been used to mineralize SARS-CoV-2 pharmaceutical compounds, and the efficiencies are greater than 65%. According to the results, photocatalysis is the main technology currently applied to remove these pharmaceuticals. This process has garnered attention because solar energy can be directly utilized; however, low photocatalytic efficiencies and high costs in large-scale practical applications limit its use. Furthermore, pharmaceuticals in the environment are diverse and complex. Finally, the review also provides ideas for further research needs and major concerns.

Removal of METH through Tertiary or Advanced Treatment in a WWTP

METHs are drugs that enter wastewater through the feces and urine of users. Conventional wastewater treatment plants are not capable of removing this type of emerging contaminant, but, in recent years, techniques have been developed to abate drugs of abuse. The present investigation focused on obtaining the technique that keeps the best balance between the comparison criteria considered: efficiency; costs; development stage; and waste generation. That is why a bibliographic review was carried out in the scientific databases of the last eight years, concluding that the six most popular techniques are: SBR, Fenton reaction, mixed-flow bioreactor, ozonation, photocatalysis, and UV disinfection. Subsequently, the Saaty and Modified Saaty methods were applied, obtaining a polynomial equation containing the four comparison criteria for the evaluation of the techniques. It is concluded that the UV disinfection method is the one with the best relationship between the analyzed criteria, reaching a score of 0.8591/1, followed by the Fenton method with a score of 0.6925/1. This research work constitutes a practical and easy-to-use tool for decision-makers, since it allows finding an optimal treatment for the abatement of METHs.

Electrosorption of phenolic compounds from olive mill wastewater: Mass transport consideration under a transient regime through an alginate-activated carbon fixed-bed electrode

Olive mill wastewater (OMWW) is an environmentally critical effluent, specifically due to its high content of phenolic compounds (PCs), which are hazardous due to their antimicrobial activities in water. However, their properties have good health effects at suitable doses. For the first time, the electrosorption of PCs from actual OMWW has been proposed for their possible recovery as value-added compounds, while decontaminating OMWW. A bio-sourced alginate-activated carbon (AC) fixed-bed electrode was prepared based on the reuse of olive pomace solid waste as powdered AC. At the optimal AC content (1% w/v), the internal ohmic drop voltage was lower (2.26 V) and the mass transport coefficient was higher (9.7 10^-5 m s^-1) along with the diffusivity (7.3 10^-9 m² s^-1), which led to enhanced electrosorption rates. Afterward, an optimal electrode potential was obtained (-1.1 V vs. Ag/AgCl), while higher voltages led to faradaic reactions. Moreover, the adsorption capacity was lower (123 mg g^-1) than that of electrosorption (170 mg g^-1) and was even higher (307 mg g^-1) with actual effluents. This was probably due to the influence of electromigration, which was confirmed by new models that could predict the electrosorption kinetics well considering mass transport and acid dissociation constants.

A critical review on the electrosorption of organic compounds in aqueous effluent - Influencing factors and engineering considerations

Despite being an old process from the end of the 19^th century, electrosorption has attracted renewed attention in recent years because of its unique properties and advantages compared to other separation technologies and due to the concomitant development of new porous electrode materials. Electrosorption offer the advantage to separate the pollutants from wastewater with the possibility of selectively adsorbing and desorbing the targeted compounds. A comprehensive review of electrosorption is provided with particular attention given to the electrosorption of organic compounds, unlike existing capacitive deionization review papers that only focus on inorganic salts. The background and principle of electrosorption are first presented, while the influence of the main parameters (e.g., electrode materials, electrode potential, physico-chemistry of the electrolyte solutions, type of compounds, co-sorption effect, reactor design, etc.) is then detailed and the modeling and engineering aspects are discussed. Finally, the main output and future prospects about recovery studies and combination between electro-sorption/desorption and degradation processes are given. This review particularly highlights that carbon-based materials have been mostly employed (85% of studies) as porous electrode in organics electrosorption, while existing studies lack of electrode stability and durability tests in real conditions. These electrodes have been implemented in a fixed-bed reactor design most of the time (43% of studies) due to enhanced mass transport. Moreover, the electrode potential is a major criterion: it should be applied in the non-faradaic domain otherwise unwanted reactions can easily occur, especially the corrosion of carbon from 0.21 V/standard hydrogen electrode or the water oxidation/reduction. Furthermore, there is lack of studies performed with actual effluents and without addition of supporting electrolyte, which is crucial for testing the real efficiency of the process. The associated predictive model will be required by considering the matrix effect along with transport phenomena and physico-chemical characteristics of targeted organic compounds.

Pyrite-mediated advanced oxidation processes: Applications, mechanisms, and enhancing strategies

Proper treatment of wastewater is one of the key issues to the sustainable development of human society, and people have been searching for high-efficiency and low-cost methods for wastewater treatment. This article reviews recent studies about pyrite-mediated advanced oxidation processes (AOPs) in removing refractory organics from wastewater. The basic information of pyrite and its characteristics for AOPs are first introduced. Then, the performance and mechanisms of pyrite-mediated Fenton oxidation, electro-Fenton oxidation, and persulfate oxidation processes are carefully reviewed and presented. Natural pyrite is an abundant low-cost heterogeneous catalyst for AOPs, and the slow release of Fe²⁺ and the self-regulation of solution pH are highlighted characteristics of pyrite-mediated AOPs. In AOPs, the interaction between Fe³⁺ and pyrite facilitates the Fe²⁺ regeneration and the Fe²⁺/Fe³⁺ cycle. Making pyrite into nanoparticles, assisting by ultrasound and light irradiation, and adding exogenous Fe³⁺, organic chelating agents, or biochar is effective to enhance the performance of pyrite-mediated AOPs. Based on the analyses of those pyrite-mediated AOPs and their enhancing strategies, the future development directions are proposed in the aspects of toxicity research, mechanism research, and technological coupling.

Enhancing the removal efficiency of methylene blue in water by fly ash via a modified adsorbent with alkaline thermal hydrolysis treatment

High efficiency of methylene blue adsorbent from waste coal fly ash by treatment with alkaline thermal hydrolysis.