Use Of Advanced Oxidation Processes Research Articles

Al-water reaction generates metastable aluminum cluster ions and their use in advanced oxidation processes

Our previous work indicated that hydroxyl radicals (HO•) exist in the filtrate of Al + acid + H2O2 system. In this work, the behind mechanism was investigated in detail and a new catalyst for advanced oxidation processes (AOPs) was found for the first time. It was revealed that metastable hexacoordinated aluminum cluster ions ([Al(H2O)63+]*), which are produced by Al-water reaction, can be as direct catalyst and decompose H2O2 into HO• in a full pH range (2.5–12.0), and efficiently degrade and mineralize organic pollutants without precipitates. Of course, their catalytic activity in acidic aqueous solution is higher than that in neutral and alkaline solutions. Furthermore, [Al(H2O)63+]* cluster ions have an excellent recyclability and their catalytic efficiency for generating HO• and degrading phenol and bisphenol A (BPA) did not decrease significantly even the cycling number was up to ten. Meanwhile, [Al(H2O)63+]* cluster ions have a long lifetime and can keep their catalytic activity for more than three months under ambient condition. The present finding shows that Al3+ ions can be also as a cost-efficient catalyst for AOP technology.

Fabrication of zinc oxide nanorods for photocatalytic degradation of docosane, a petroleum pollutant, under solar light simulator.

The use of advanced oxidation processes (AOP) in photocatalysis is critical for treating hazardous chemical compounds in oil-produced water (OPW). ZnO NRs are one of the most important modern and safe photocatalysts and have been easily prepared by a microwave-assisted hydrothermal method and grown on glass substrates. Hexagonal-shaped ZnO NRs and a bandgap energy (Eg) of up to 3.2 eV were characterized using SEM, XRD, UV-Vis, and PL devices, respectively. The effectiveness of photocatalytic degradation on the organic docosane solution was evaluated using a solar light simulator. On the surface area of the ZnO NRs, high photon absorption causes e-/h+ pairs to be excited between the VB and CB, producing free radicals that immediately react with organic contaminants and transform them into harmless chemicals. The photocatalytic degradation efficiency of the compound docosane analysed using GC-MS/MS reached 68.5% at 5 hours of irradiation. A mechanism for the photocatalytic degradation of docosane was proposed at pH ∼ 6.5, and a reduction of 60.5% of the total organic carbon (TOC) was achieved. Thus, the photocatalytic treatment of organic compounds contained in OPW has great potential and serves an important environmental purpose.

Procesos de oxidación avanzada utilizados en el tratamiento de sustancias perfluoroalquiladas en agua

Perfluoroalkylated and polyfluoroalkylated substances (PFAS) are a large family of synthetic chemicals widely used to manufacture various commercial products. However, they are hazardous to health and the environment. These substances are very persistent and their degradation requires advanced degradation techniques. One of the most widely used technologies for this purpose is advanced oxidation processes (AOP). This study aims to evaluate the use of AOP in PFAS degradation based on their efficiency, parameters influencing each process, advantages, disadvantages, and associated research challenges. According to the results, plasma, electrochemical oxidation, sonochemical oxidation, and heterogeneous photocatalysis stand out among the AOP applied for PFAS degradation. In addition, perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) were found to be the main toxic compounds studied. In this regard, future research should focus on a wider variety of PFAS. Finally, the drawbacks associated with the application of these processes to eliminate the substances of interest were found to be an urgent need to be overcome.

Ketoprofen and diclofenac removal and toxicity abatement in a real scale sewage treatment Plant by photo-Fenton Process with design of experiments

The disposal of effluent and sludge containing emerging contaminants (ECs) are the main problems associated with most traditional treatment methods. Non-steroidal anti- inflammatory drugs (NSAIDs) require more complete treatments integrated with conventional processes to enable circular economy and the water-energy-food (WEF) nexus. Different options to traditional technologies have been employed in the treatment of effluents, such as advanced oxidation processes (AOPs). However, few studies use real scales integrated with existing technologies. This work evaluated the use of AOPs for the degradation of ketoprofen (KET), diclofenac (DCF), and the DCF+KET mixture in an anaerobic effluent matrix, post-treated by an Upflow Anaerobic Sludge Blanket Reactor (UASB) in a real-scale Sewage Treatment Plant (STP). A Factorial Experimental Design was proposed and after 2 h of treatment the efficiency was evaluated by the decrease in total organic carbon (TOC), decrease of drugs concentration, physicochemical and ecotoxicity parameters. As a result, the photo-Fenton process showed greater efficiency in the degradation of KET (97.2% ± 1.6), DCF (72.7% ± 4.9), and the mixture of the two drugs DCF+KET (66.0% ± 2.5), improved the quality of the effluent in the removal of COD, BOD, and turbidity, and reduced toxicity in tests performed with Artemia sp. and Lactuca sativa. The integration between AOPs and UASB as a sewage treatment technology widely used as primary and secondary treatment, allowed to optimize the sewage treatment system for an ideal arrangement. As a consequence, it possesses the capacity to eliminate conventional organic matter and efficiently degrade emerging pollutants.

The production of highly efficientvisible‐light‐driven electrospunα‐Fe2O3photocatalyst through modifying iron source material for wastewater treatment applications

AbstractBackgroundHeterogeneous photocatalysis has been considered one of the most attractive methods in the wastewater remediation process due to allowing continuous re‐use, the reactions taking place at room temperature, and photocatalysts are inexpensive.ObjectiveWith the optimization of the structural properties of hematite at the nanometer level by utilizing engineering strategies such as morphology regulation, and shape control, it is possible to enhance its photocatalytic performance. The study's main objective is to improve photocatalytic performances of visible‐light photoactive hematite materials produced by engineering strategies.MethodsThe α‐Fe2O3photocatalyst fibres with highly porous were fabricated by electrospinning method, allowing extraordinary length, a large ratio of length to diameter, hierarchically porous structure, high surface area, small grain sizes, and high porosity.ResultsIn the heterogeneous photocatalysis of the electrospun α‐Fe2O3nanofibers against two model dyes representing anionic (MO) and cationic (RhB) characteristics, both electrospun α‐Fe2O3nanofibers showed good photocatalytic activity against used model pollutants. The α‐ α‐Fe2O3nanofibers produced using iron(III) chloride hexahydrate exhibited a higher photocatalytic degradation rate against both dye pollutants relative to the α‐ α‐Fe2O3nanofibers produced using iron(III) chloride.ConclusionsDepending on the used iron sources and associatively their final morphological characteristics, it was observed that their photocatalytic degradation performances were seriously affected. It is suggested that electrospun α‐Fe2O3nanofibers, especially those with highly porous and smaller diameters, are suitable candidates as a visible‐light‐driven semiconductor material to use in advanced oxidation processes for removing pollutants from wastewater.

From Fenton and ORR 2e−-Type Catalysts to Bifunctional Electrodes for Environmental Remediation Using the Electro-Fenton Process

Currently, the presence of emerging contaminants in water sources has raised concerns worldwide due to low rates of mineralization, and in some cases, zero levels of degradation through conventional treatment methods. For these reasons, researchers in the field are focused on the use of advanced oxidation processes (AOPs) as a powerful tool for the degradation of persistent pollutants. These AOPs are based mainly on the in-situ production of hydroxyl radicals (OH•) generated from an oxidizing agent (H2O2 or O2) in the presence of a catalyst. Among the most studied AOPs, the Fenton reaction stands out due to its operational simplicity and good levels of degradation for a wide range of emerging contaminants. However, it has some limitations such as the storage and handling of H2O2. Therefore, the use of the electro-Fenton (EF) process has been proposed in which H2O2 is generated in situ by the action of the oxygen reduction reaction (ORR). However, it is important to mention that the ORR is given by two routes, by two or four electrons, which results in the products of H2O2 and H2O, respectively. For this reason, current efforts seek to increase the selectivity of ORR catalysts toward the 2e− route and thus improve the performance of the EF process. This work reviews catalysts for the Fenton reaction, ORR 2e− catalysts, and presents a short review of some proposed catalysts with bifunctional activity for ORR 2e− and Fenton processes. Finally, the most important factors for electro-Fenton dual catalysts to obtain high catalytic activity in both Fenton and ORR 2e− processes are summarized.

Photocatalytic Degradation of Bentazon Pesticide by a Fe2O3-TiO2 Composite Catalyst Irradiated by UVA, UVB, and Natural Light

Environmental pollution by contaminants of emerging concern, among these various pesticides, has been a concern of environmentalists and scientists around the world. Thus, efforts to mitigate the impacts of these substances have been carried out, and the use of advanced oxidation processes, such as photocatalysis, is an alternative. This work sought to synthesize a composite photocatalyst based on iron oxides and titanium dioxide to assess its applicability in degrading the herbicide bentazon (BTZ) by a lamp that simulates the solar spectrum (visible, ultraviolet A and ultraviolet B) and sunlight. Photocatalytic degradation reached 51% in 120 min with a rate constant k = 0.0058 min−1 when a UV-Vis lamp of 300 W was used. The applicability was demonstrated under sunlight radiation, reaching 38% degradation of a bentazon solution (4.1 × 10−4 mol L−1) after 320 min. TiO2 and Fe2O3 were synthesized similarly but showed no degradation under the same conditions. Thus, Fe2O3-TiO2 is an inexpensive and non-toxic material capable of efficiently conducting the photocatalytic degradation of organic compounds, such as the bentazon herbicide.

Primary photoprocesses for Fe(III) complexes with citric and glycolic acids in aqueous solutions

The mechanism of UV photolysis of Fe(III) complexes with citric ([FeCit] and [Fe(OH)Cit]−) and glycolic ([FeGlyc]+) acids was revealed. The excitation of the complexes leads to the predominant formation of corresponding long-lived radical complexes exhibiting a low-intensity absorption band in the visible region (λmax = 600, 550 and 660 nm for ([FeCit], [Fe(OH)Cit]− and [FeGlyc]+ complexes, accordingly). The primary quantum yields of photolysis at 355 nm are 0.17, 0.28 and 0.12 for these complexes, accordingly. The decomposition of radical complexes leads to the appearance of corresponding organic radicals in solution, which are further oxidized in competitive processes by the initial complexes and dissolved oxygen. This enhances quantum yields of generation of ferrous ions in steady-state conditions and can also lead to a good yield of hydroxyl radicals in subsequent Fenton-like reactions in the presence of dissolved oxygen. The further study of the efficiency of OH radical generation upon excitation of these systems are urgently needed in order to estimate their role in environmental aqueous chemistry and to assess their potential use in advanced oxidation processes.

A review toward contaminants of emerging concern in Brazil: Occurrence, impact and their degradation by advanced oxidation process in aquatic matrices.

This work presents data regarding the occurrence and treatment of Contaminants of Emerging Concern (CECs) in Brazil in the past decade. The literature review (2011-2021) revealed the detection of 87 pharmaceutical drugs and personal care products, 58 pesticides, 8 hormones, 2 illicit drugs, caffeine and bisphenol A in distinct matrices (i.e.: wastewater, groundwater, sea water, rainwater, surface water, drinking water and hospital effluent). Concentrations of CECs varied from ng-μg L-1 depending on the location, compound and matrix. The inefficiency of conventional wastewater treatment methods on the removal of CECs and lack of basic sanitation in some regions in the country aggravates contamination of Brazilian aquatic environments and poses potential environmental and health risks. Advanced oxidation processes (AOPs) are pointed out as viable and efficient alternatives to degrade CECs and prevent environmental contamination. A total of 375 studies involving the use of AOPs in Brazilian aqueous matrices were published in the last decade. Fenton and photo-Fenton processes, photo-peroxidation, ozonation, electrochemical advanced oxidation and heterogeneous photocatalysis are some of the AOPs applied by Brazilian research groups. Although many works discuss the importance of applying these technologies for CECs removal in real treatment plants, most of these studies assess the treatment of distilled water or simulated effluent. Therefore, the conduction of studies applying AOPs in real matrices are critical to drive the implementation of these processes coupled to conventional water and wastewater treatment in real plants in order to prevent the contamination of environmental matrices by CECs in Brazil.

Insights into current physical, chemical and hybrid technologies used for the treatment of wastewater contaminated with pharmaceuticals

The purpose of this article is to review the current physical, chemical and hybrid technologies practices employed in the removal of pharmaceuticals from liquid effluents originating from various resources including municipal waste, hospitals discharge with a focus on pharmaceutical manufacturing industry. Pharmaceutical pollutants are mostly persistent organic compounds that are not easily removed by conventional wastewater treatment processes. The literature reviewed shows that advanced oxidation processes are able to degrade these persistent pharmaceuticals. However, the oxidation may also introduce toxic oxidation intermediates/by-products if these processes are not properly monitored and operated. Physical treatments, like carbon adsorption and membrane filtration, can provide a barrier that prevents both parent compounds and toxic intermediates passing into treated wastewater. However, these processes are phase changing technologies in which contaminants are transferred from one phase to another hence, the retentate water and absorbent require further treatment, and properly managed disposal. The combination of different processes can be an ideal treatment scheme, for the retention and degradation of both parent and transformation compounds. Through hybrid technologies, the advantages of the methods are combined, leading to a maximization of contaminants removal. The review highlights the importance of installing combined wastewater treatment processes to reduce the amounts of pharmaceutical residues before the wastewater enters the environment. The use of advanced oxidation process, either as a pre-treatment or as a post-treatment combined with biological, adsorption, or filtration process is recommended as a promising option. Nevertheless, the optimum treatment methods for the pharmaceuticals-containing wastewater depends on the quality and quantity of wastewater, as well as on the pharmaceutical compounds residues and their hazardous effects. • Evidence of pharmaceuticals including antibiotics in aquatic environment. • Physicochemical processes have high removal efficiency and short treatment duration. • AOPs and their combination with physicochemical processes are promising options. • Hybrid technology can provide a solution for pharmaceutical wastewater treatment.

Decolorization and degradation of methylene blue by photo-Fenton reaction under visible light using an iron-rich clay as catalyst: CCD-RSM design and LC-MS technique

In this work, an iron-rich bentonite was thermally modified at 200 oC and posteriorly used as a heterogeneous catalyst in the decolorization and degradation of methylene blue dye (MB) by photo-Fenton reaction under visible irradiation. The variables such as catalyst concentration and pH were investigated in the reaction system to detect the optimal decolorization conditions using the response surface methodology (RSM) coupled with Central Composite Design (CCD). Photodegradation of MB was analyzed by LC-MS technique. The results indicated that the optimal conditions to obtain 94% of MB decolorization efficiency were pH = 2.4 and catalyst mass = 0.02 g. It was also possible to verify that the simultaneous combination of catalyst, hydrogen peroxide and visible light in the reaction medium was primordial for the increasing MB decolorization efficiency. MB degradation occurred partially at 180 min of photo-Fenton reaction, since the presence of dye in the solution was reduced, leading to its transformation into different intermediate products. Therefore, the catalyst used in this work has demonstrated a great potential for the degradation of cationic dye, allowing its use in advanced oxidation processes

Deriving an ɑ-Fe2O3/g-C3N4 nanocomposite from a naturally hematite-rich soil, for dual photocatalytic and photo-Fenton degradation of Acetaminophen under visible light

In this study, a facile synthesis route was reported for the fabrication of an ɑ-Fe2O3@g-C3N4 (FeCN) photocatalyst, derived from a hematite-rich soil. Among the various as-made catalysts prepared using different weights of hematite, FeCN-0.5 showed the best catalytic performance in Acetaminophen (ACT) degradation under visible light irradiation with high mineralization efficiency. The superb activity of this photocatalyst results from a Z-scheme structure formation between ɑ-Fe2O3 and g-C3N4 that increased the light adsorption capacity, facilitated the generation of charge-carries, and increased the generated electrons that participated in Fe3+/Fe2+ cycles, thus enhancing the photo-Fenton reaction. UV–Vis diffuse reflection spectroscopy (DRS) and photoluminescence analysis (PL) confirmed the excellent separation of charge carriers in the as-made photocatalyst. The reaction rate of the FeCN-0.5/Vis/H2O2 process was around 3, and 7 times of that in the FeCN-0.5/Vis and FeCN-0.5/H2O2 processes respectively, which indicated the synergy effect of the involved processes in ACT degradation. Based on the radical trapping experiments, hydroxyl radical (HO∙) was the dominant reactive species in ACT degradation. The catalyst showed high stability in consecutive reuse cycles. Overall, this study provides new insights into the fabrication of novel materials derived from natural sources, suitable for their use in advanced oxidation processes.

Recent Developments in Advanced Oxidation Processes for Organics-Polluted Soil Reclamation

Soil pollution has become a substantial environmental problem which is amplified by overpopulation in different regions. In this review, the state of the art regarding the use of Advanced Oxidation Processes (AOPs) for soil remediation is presented. This review aims to provide an outline of recent technologies developed for the decontamination of polluted soils by using AOPs. Depending on the decontamination process, these techniques have been presented in three categories: the Fenton process, sulfate radicals process, and coupled processes. The review presents the achievements of, and includes some reflections on, the status of these emerging technologies, the mechanisms, and influential factors. At the present, more investigation and development actions are still desirable to bring them to real full-scale implementation.

A review on future wastewater treatment technologies: micro-nanobubbles, hybrid electro-Fenton processes, photocatalytic fuel cells, and microbial fuel cells.

The future prospect in wastewater treatment technologies mostly emphasizes processing efficiency and the economic benefits. Undeniably, the use of advanced oxidation processes in physical and chemical treatments has played a vital role in helping the technologies to remove the organic pollutants efficiently and reduce the energy consumption or even harvesting the electrons movements in the oxidation process to produce electrical energy. In the present paper, we review several types of wastewater treatment technologies, namely micro-nanobubbles, hybrid electro-Fenton processes, photocatalytic fuel cells, and microbial fuel cells. The aims are to explore the interaction of hydroxyl radicals with pollutants using these wastewater technologies, including their removal efficiencies, optimal conditions, reactor setup, and energy generation. Despite these technologies recording high removal efficiency of organic pollutants, the selection of the technologies is dependent on the characteristics of the wastewater and the daily production volume. Hence the review paper also provides comparisons between technologies as the guidance in technology selection.

A Review of Manganese(III) (Oxyhydr)Oxides Use in Advanced Oxidation Processes.

The key role of trivalent manganese (Mn(III)) species in promoting sulfate radical-based advanced oxidation processes (SR-AOPs) has recently attracted increasing attention. This review provides a comprehensive summary of Mn(III) (oxyhydr)oxide-based catalysts used to activate peroxymonosulfate (PMS) and peroxydisulfate (PDS) in water. The crystal structures of different Mn(III) (oxyhydr)oxides (such as α-Mn2O3, γ-MnOOH, and Mn3O4) are first introduced. Then the impact of the catalyst structure and composition on the activation mechanisms are discussed, as well as the effects of solution pH and inorganic ions. In the Mn(III) (oxyhydr)oxide activated SR-AOPs systems, the activation mechanisms of PMS and PDS are different. For example, both radical (such as sulfate and hydroxyl radical) and non-radical (singlet oxygen) were generated by Mn(III) (oxyhydr)oxide activated PMS. In comparison, the activation of PDS by α-Mn2O3 and γ-MnOOH preferred to form the singlet oxygen and catalyst surface activated complex to remove the organic pollutants. Finally, research gaps are discussed to suggest future directions in context of applying radical-based advanced oxidation in wastewater treatment processes.

МІКРО- І НАНОСТРУКТУРОВАНИЙ ТИТАНУ(IV) ОКСИД У СОНО-, ФОТО- І СОНОФОТОКАТАЛІТИЧНІЙ ДЕГРАДАЦІЇ КСАНТЕНОВОГО БАРВНИКА РОДАМІНУ Б (ОГЛЯД)

Adsorption methods for removing Rhodamine B from wastewater and oxidative degradation methods based on the use of advanced oxidation processes (sonolysis, photolysis, sono-, photo- and sonophotocatalysis) are considered. It was established that naturally occurring materials (such as clays, zeolites, coal ash, anaerobic sludge, agricultural solid wastes) and their modified or activated analogues are used as adsorbents for the removal of Rhodamine B. The possible mechanism of photo- and sonophotocatalytic degradation of Rhodamine B in the presence of micro- and nanostructured titanium (IV) oxide is presented. The effectiveness of its application for degradation of Rhodamine B is analyzed.

Advanced oxidation processes of coumarins by hydroperoxyl radical: An experimental and theoretical study, and ecotoxicology assessment

Coumarin derivatives are an example of stable molecules with very complex biodegradation routes in wastewaters. The use of advanced oxidation processes offers a way to their chemical modification to less toxic products. In this study, the experimental reactivity of 4-hydroxycoumarin (1) and its two derivatives towards hydroperoxyl radical (HOO•) was proven by the ESR spectroscopy. The absence of measurable concentration of carbon- and oxygen-centered radicals, except for DEPMPO-HOO• adduct, showed that stable products were formed in the reaction. Two novel mechanisms, namely hydrogen atom abstraction - radical–radical coupling (HAT-RRC) and radical adduct formation-hydrogen atom abstraction (RAF-HAA) were suggested as possible reaction routes between HOO• and coumarin derivatives. Thermodynamic and kinetic parameters were investigated in detail to explain the plausibility of these two mechanisms with special emphasis on the determination of the most active positions. The theoretical calculations were accompanied by the Natural Bond Orbital Theory and Quantum Theory of Atoms in Molecules. The thermodynamically preferred mechanism of the reaction was RAF-HAA, while the highest reaction rate was obtained for the position C3 of 1. The preferred mechanism was further verified by the UV–Vis spectrophotometry and excited state optimization. The examined routes lead to the formation of stable products with lower toxicity towards aquatic organisms, as shown by the eco-toxicology assessment.

Advanced oxidation processes for chlorpyrifos removal from aqueous solution: a systematic review.

Chlorpyrifos (CPF), an organophosphate insecticide, due to its high efficiency and low cost is widely used in the agricultural industry. CPF may lead to lung deficiency, central nervous system damage, developmental and autoimmune disorders. In recent decades, the advanced oxidation processes (AOPs) have been considered in water and wastewater treatment due to their high efficiency in decomposition of organic and inorganic compounds, specially hardly biodegradable or non-biodegradable compounds. In the present review study, the most common AOPs (such as Fenton and Photo-Fenton processes, UV/H2O2 photolysis, UV/TiO2 heterogeneous photo catalysis, electrochemical processes, sonolysis technology, gamma irradiation technology and sulfate-based AOPs) applied for CPF removal from aqueous matrices has been investigated. It can be concluded that the use of AOPs are effective for CPF removal from aqueous media. In addition, Fenton and photocatalytic processes appear to be the most common techniques for CPF degradation.

Combined AOP/GAC/AOP systems for secondary effluent polishing: Optimization, toxicity and disinfection

This study reports the use of advanced oxidation processes (AOPs), specifically O3, O3/H2O2 and UV/H2O2, in combination with granular activated carbon (GAC) to polish secondary effluents. For this purpose, three configurations were tested: O3-GAC-O3, O3/H2O2-GAC-O3/H2O2 and UV/H2O2-GAC-UV/H2O2. The efficiency evaluation was based on the ability of the systems to remove aromaticity (UV254), organic matter (chemical oxygen demand - COD), Escherichia coli and total coliforms content as well as toxicity (Artemia salina and Allium cepa). The methods were optimized using central composite design to investigate the influence of O3 and H2O2 concentration in the efficiency of the system and the optimal conditions were subsequently applied to treat urban secondary effluents. High organic matter removal rates were obtained by all the tested configurations, of which O3-GAC-O3 proved to be the most efficient. The systems were also efficient to disinfect the samples, promoting nearby 5-log reduction of E. coli and total coliforms. Acute toxicity, cytotoxicity, and genotoxicity were observed in samples subjected to the UV/H2O2-GAC-UV/H2O2 method. When used alone, GAC removed around 80% of organic matter, nevertheless failed to disinfect the samples, which furthermore exhibited acute toxicity and genotoxicity toward A. cepa. Samples subjected to direct photolysis proved more toxic than untreated samples while uncombined H2O2, O3, GAC, and UV, as well as O3/H2O2 and UV/H2O2 failed to degrade organic matter or to mitigate the toxicity of the samples.

Progress in applications of advanced oxidation processes for promotion of biohydrogen production by fermentation processes

Advanced oxidation processes (AOPs) are powerful methods for treating substrates using radicals that are generated in situ. This study reviewed applications of AOPs in enhancement of biohydrogen production. The AOPs are applied in substrate pretreatment because of their ability to break the complex structure of lignocellulosic biomass for ease of subsequent hydrolysis. The mechanism of solubilization of complex organics resulting in increased biodegradability of substrate during pretreatment has been suggested. Documented studies indicate that up to 98% color removal from organic wastewater is possible by the use of AOPs. Furthermore, a combination of AOPs with biological processes can achieve more than 90% COD removal from biohydrogen production effluent. Sonication, microwave-enhanced AOPs, and electrochemical treatment are the most applied AOPs in enrichment of biohydrogen with up to fivefold increase in biohydrogen yield achieved after electrochemical pre-treatment. The mechanism of enhancement of hydrogen yield in dark fermentation after pretreatment of the substrate and inoculum with AOPs has been proposed. The excess sludge produced during hydrogen fermentation can be pretreated with ozone and ultrasound before biomethanation process. More studies on co-production of biohydrogen and electricity through electrochemical oxidation in fuel cells are necessary. This study proposes the integration of AOPs with conventional processes in biorefinery production approach with aim of improving biohydrogen yields, co-producing it with other biofuels, and reducing the process costs. Future studies should focus on the scale-up of AOPs for commercial applications. Comparative studies on energy requirements for various AOPs applications are lacking and should be carried out. Graphical abstract