A Review of Various Advanced Oxidation Techniques for Pesticide Degradation for Practical Application in Aqueous Environments

Abstract

Pesticides are chemicals used in agriculture, industry, and households to control pests and enhance crop yields but have emerged as pollutants in soil and water due to their presence in domestic and agricultural wastewater effluents. The World Health Organization (WHO) has identified the development of pesticide resistance as a significant threat to global public health. Consequently, removing pesticides in aqueous environments has gained considerable attention. Numerous methodologies, including biological, physical, and chemical methods, have been employed for their treatment. Among these methods, advanced oxidation processes (AOPs) have garnered particular interest due to their fast reaction rates and strong oxidizing abilities. This review focuses on various AOPs such as Fenton and Fenton-like oxidation, ozonation, the UV/H₂O₂ process, electrochemical oxidation, photocatalytic oxidation, and the UV/O₃ process. The review analyzes and summarizes the current applications of these AOPs for treating pesticides in aqueous environments. It also compares various AOPs treatment methods and discusses the challenges, drawbacks, advantages, and strategies for addressing these issues, and provides insights into the future prospects. Finally, it propose potential strategies and areas of improvement for future research to enhance the efficiency and sustainability of AOPs in practical application.

1. Introduction

Pesticides play a crucial role in agriculture by protecting crops from pests, diseases, and weeds. They enhance food production and contribute to global food security. However, the widespread and often indiscriminate use of pesticides has led to their accumulation in the environment, presenting significant challenges and risks [1]. One key concern is the contamination of water sources, both surface water and groundwater, with pesticide residues. Pesticides can enter water bodies through runoff from agricultural fields, leaching from soil, and improper handling or disposal practices. This contamination poses a threat to aquatic ecosystems, drinking water supplies, and non-target organisms, including beneficial insects, birds, and mammals [2]. To address this issue, effective and environmentally friendly pesticide treatment methods are essential. First and foremost, the removal of pesticide residues from water sources is necessary to safeguard human health. Consumption of pesticide-contaminated water can lead to acute or chronic toxic effects, especially if the concentrations exceed regulatory limits [3]. Furthermore, the preservation of aquatic ecosystems is crucial. Pesticides can have detrimental effects on various aquatic organisms, such as fish, amphibians, and invertebrates. Even at low concentrations, these chemicals can disrupt reproductive systems, impair growth and development, and induce behavioral changes in aquatic life. By treating water sources contaminated with pesticides, we can help protect the balance and biodiversity of aquatic ecosystems [4].

The use of environmentally friendly methods for pesticide treatment is vital to minimize the negative impact on the environment. Traditional treatment methods, such as activated carbon filtration or chemical precipitation, have limitations in terms of efficiency and selectivity. These methods may also generate harmful byproducts or require extensive post-treatment processes [3]. Emphasizing the importance of environmentally friendly alternatives, advanced oxidation processes are gaining recognition. AOPs offer effective treatment solutions while considering environmental compatibility. By utilizing oxidation techniques like ozone, hydrogen peroxide, and UV radiation, AOPs can degrade pesticide residues and transform them into harmless byproducts. This approach minimizes the introduction of additional pollutants and promotes the sustainable management of pesticide-contaminated water sources [5]. Pesticide treatment plays a crucial role in protecting human health, preserving aquatic ecosystems, and ensuring environmental sustainability. With the increasing need for safer and more effective methods, the development and implementation of environmentally friendly approaches, such as AOPs, are essential for addressing pesticide contamination and mitigating its adverse effects on ecosystems and society at large [6].

Advanced oxidation processes are chemical treatment methods used to facilitate the degradation of organic contaminants in water and wastewater. AOPs employ the generation of highly reactive hydroxyl radicals (^•OH) to oxidize and break down various organic compounds into harmless substances or lower toxicity intermediates [7]. In the context of pesticide treatment, AOPs offer a promising solution for the removal of pesticide residues from water sources. AOPs can effectively degrade and eliminate pesticide residues [8,9]. This involves the application of advanced oxidation techniques like ozone (O₃), hydrogen peroxide (H₂O₂), and ultraviolet (UV) radiation, either individually or in combination, to generate ^•OH radicals. These radicals possess strong oxidative power, enabling them to attack and break the chemical bonds of various organic compounds, including pesticide molecules [10]. The AOPs’ potential lies in their ability to degrade a wide range of organic contaminants, including highly resistant pesticides. They can effectively transform complex pesticide structures into simpler and less toxic byproducts. By using AOPs, it becomes possible to treat water contaminated with different pesticide classes, such as herbicides, insecticides, and fungicides [5,11]. Advanced oxidation processes (AOPs) offer advantages in terms of efficiency, selectivity, and environmental compatibility. They can be tailored to target specific pesticide compounds based on their reactivity and structure. Additionally, AOPs are capable of mineralizing pesticides into carbon dioxide (CO₂) and water (H₂O), reducing or eliminating the presence of potentially harmful byproducts [12]. The objective of this review is to explore and evaluate different types of advanced oxidation processes in treating wastewater contaminated with pesticides. By analyzing existing studies and research findings, the review aims to compare the effectiveness of various advanced oxidation methods in terms of their efficiency, advantages, limitations, and applicability in the practical treatment of pesticide-contaminated wastewater, and suggestions for future research are proposed.

2. Pesticides in Aqueous Environments

2.1. Sources of Pesticide Contamination in Aqueous Environments and Their Environmental Impact

The Figure 1 shows that pesticide contamination in wastewater stems from various sources, primarily agricultural runoff and urban activities. In agricultural settings, pesticides are widely used to protect crops from pests and diseases [13]. However, excess application or improper handling can lead to runoff during rainfall events, carrying pesticides into nearby water bodies or infiltrating groundwater. Additionally, urban areas contribute to pesticide contamination through the use of lawn and garden pesticides, as well as pest control measures in households and public spaces. Stormwater runoff from urban surfaces can transport these chemicals into sewage systems, further exacerbating contamination issues [14]. Furthermore, industrial activities such as manufacturing and chemical production may also contribute to pesticide pollution through improper disposal practices or accidental spills, adding to the complexity of managing pesticide contamination in wastewater systems. Efforts to mitigate pesticide pollution require a multifaceted approach, including improved agricultural practices, stricter regulations on pesticide use, and enhanced wastewater treatment methods to safeguard water quality and ecosystem health [13].

Pesticide contamination in aquatic systems arises from multiple anthropogenic sources, each contributing distinct chemical loads to waterways (Figure 2). Urban activities, including residential lawn care and structural pest control, account for approximately 15–20% of pesticide runoff in watersheds, with herbicides like 2,4-D and glyphosate being frequently detected. Agricultural runoff is the dominant contributor, responsible for 60–70% of pesticide influx, driven by excessive application of insecticides (e.g., neonicotinoids) and fungicides, which leach into rivers during rainfall events. Industrial practices, though less prevalent (5–10%), pose acute risks due to improper disposal of concentrated agrochemicals and accidental spills, often involving persistent organic pollutants (POPs) such as DDT residues. Mitigating these impacts requires targeted regulatory measures, including buffer zones for farms, integrated pest management (IPM) in urban areas, and stricter industrial waste protocols.

2.2. Pesticide Pollution Impacts on Health and Ecosystems

Pesticide pollution presents significant health and environmental risks to both human populations and ecosystems. Human health impacts arise from exposure pathways like consuming contaminated food and water, inhaling pesticide residues, and direct skin contact during agricultural activities. Chronic pesticide exposure is associated with various health issues, including cancer, reproductive disorders, and neurological ailments, with children and pregnant women being especially vulnerable [15]. Environmental consequences encompass soil, water, and air contamination, disrupting ecosystems, causing biodiversity loss, and affecting non-target organisms like beneficial insects and aquatic life through toxicity and habitat disturbances. Pesticides persist in the environment, leading to bioaccumulation and biomagnification, with long-term repercussions on ecosystems. The degradation of water quality due to pesticide runoff from agricultural areas and improper disposal practices threatens aquatic life, safe drinking water sources, and agricultural productivity by compromising essential water resources [16].

Figure 3 indicates that pesticide pollution poses significant risks to both human health and environmental stability. Vulnerable populations, such as children and pregnant women, face heightened susceptibility due to developmental sensitivity; studies link prenatal pesticide exposure to a 20–30% increased risk of neurodevelopmental disorders. Environmental contamination disrupts aquatic and terrestrial ecosystems, with glyphosate and neonicotinoids reducing pollinator populations by up to 40% in high-exposure regions [17] and contaminating 60% of global freshwater systems. Human health risks from chronic exposure include elevated incidences of specific cancers (e.g., non-Hodgkin lymphoma), reproductive disorders (e.g., reduced fertility), and Parkinson’s disease. These findings underscore the urgency of adopting stricter regulatory measures and sustainable alternatives, such as integrated pest management (IPM), to mitigate long-term harms.

2.3. Pesticide Classification, Chemical Stability, and the Need for AOPs

Pesticides are broadly classified based on their target organisms into insecticides, herbicides, fungicides, rodenticides, and algaecides, each featuring distinct chemical frameworks optimized for environmental persistence and biological efficacy [18]. For example, insecticides such as chlorpyrifos typically contain organophosphorus structures, herbicides like 2,4-D and atrazine incorporate halogenated aromatic rings, and fungicides such as carbendazim feature heterocyclic moieties. These diverse structures confer substantial chemical stability, allowing pesticides to resist natural degradation processes such as hydrolysis, photolysis, and microbial breakdown [19]. Halogenation, aromaticity, and the presence of electron-withdrawing groups further increase resistance to conventional water treatment methods, such as biologically activated sludge processes or simple filtration, often leading to the incomplete removal of parent compounds and/or formation of persistent metabolites. Given these challenges, AOPs have emerged as essential technologies for pesticide degradation. AOPs produce highly reactive radicals, particularly hydroxyl radicals (•OH) and sulfate radicals (SO₄•⁻), capable of non-selectively attacking stable carbon–carbon bonds, aromatic systems, and halogenated structures [20]. Unlike conventional treatments that rely on selectivity or microbial adaptation, AOPs can achieve deep oxidation, facilitating complete mineralization of pesticides into CO₂, water, and inorganic ions. Thus, the application of AOPs addresses the inherent chemical resilience of modern pesticides, offering a robust and versatile solution for ensuring water quality and environmental protection, especially when combined with doped nanomaterials to suppress byproducts.

3. Overview of Advanced Oxidation Processes and Their Underlying Mechanisms of Wastewater Treatment

3.1. Fenton and Fenton-like Process

Fenton’s reaction relies on the use of hydrogen peroxide (H₂O₂) and a catalyst, typically iron (Fe), to generate hydroxyl radicals [21,22]. The iron catalyst converts hydrogen peroxide to highly reactive hydroxyl radicals at a suitable pH [23]. These hydroxyl radicals can rapidly oxidize various organic pollutants, breaking them down into simpler and less harmful compounds. The underlying mechanism involves the reaction between iron catalyst and hydrogen peroxide, forming hydroxyl radicals via the Fenton reaction (Equation (1)) [22]. Building upon this fundamental mechanism, various advanced oxidation methods have been developed, such as photo-Fenton (PF), electro-Fenton (EF), photo electro-Fenton (PEF), and solar photo electro-Fenton (SPEF) [24,25,26,27]. These methodologies aim to enhance the circulation of Fe(III)/Fe(II) species and amplify the generation of hydroxyl radicals (${}^{•}OH$) to effectively degrade recalcitrant contaminants. The mechanisms underlying these advanced processes involve (1) in situ electro-generation of H₂O₂ through the two-electron reduction of molecular oxygen (O₂) on a carbonaceous cathode (Equation (2)); (2) utilization of an electric field to facilitate the in situ regeneration of Fe(II) species at the cathode (Equation (3)) [26]; and (3) accelerated conversion of Fe(III) to Fe(II) species via photocatalytic reactions, coupled with the decomposition of H₂O₂ to generate additional hydroxyl radicals (Equations (4) and (5)) [24,25].

$$H_2{O}_2+{Fe}^{2+}\to {Fe}^{3+}+{}^{•}OH+{OH}^{-}$$

(1)

$$O_2+2H^{+}+2e^{-}\to H_2{O}_2$$

(2)

$${Fe}^{3+}+e^{-}\to {Fe}^{2+}$$

(3)

$${\mathrm{F}\mathrm{e}}^{3+}+{\mathrm{H}}_2\mathrm{O}+\mathrm{h}\mathrm{v}\to {\mathrm{F}\mathrm{e}}^{2+}+{}^{•}\mathrm{O}\mathrm{H}+{\mathrm{H}}^{+}$$

(4)

$${\mathrm{H}}_2{\mathrm{O}}_2+\mathrm{h}\mathrm{v}\to 2{}^{•}\mathrm{O}\mathrm{H}$$

(5)

The oxidation mechanism for the Fenton process is shown in Figure 4. Based on this principle, the Fenton process has been widely used in various kinds of organic wastewater treatment. The degradation efficiency of organic pollutants in the Fenton process depends on operation parameters such as wastewater pH, the concentration of Fenton reagent, and the initial organic pollutant concentration, of which wastewater pH is a highly important parameter [23].

3.2. Ozonation-Based Advanced Oxidation Process

Ozonation-based AOPs primarily degrade and mineralize refractory contaminants through two main mechanisms: (1) direct ozonation involves ozone reacting directly with target contaminants. This process encompasses redox reactions, cycloaddition reactions, electrophilic substitution reactions, and nucleophilic reactions [28]. (2) Another approach entails utilizing various physical or chemical methods to catalytically generate high redox potential reactive oxygen species (ROS) from ozone, notably hydroxyl radical (${}^{•}OH$) [29,30,31,32]. Indirect catalytic ozonation has emerged as the predominant approach for degrading and mineralizing refractory organic compounds. The synergetic effect between ozone and hydrogen peroxide has long been recognized and extensively explored by researchers for the mitigation of emerging contaminants, such as pesticides, dyes, endocrine-disrupting chemicals (EDCs), pharmaceuticals, and personal care products (PPCPs) [33,34]. This synergistic reaction between ozone and hydrogen peroxide generates powerful reactive oxygen species (ROS), particularly the hydroxyl radical (${}^{•}OH$) (Equation (6)), significantly enhancing the efficiency of removing various ozone-resistant pollutants.

$$H_2{O}_2+O_3\to {}^{•}OH+•O_2^{-}+H^{+}+O_2$$

(6)

For example, Figure 5 shows the probable pathway of phenol degradation in the catalytic ozonation process over MgO/AC. Firstly, electrophilic hydroxyl radicals preferentially attack the adjacent or para position of the benzene ring in the reaction, and phenol is oxidized to the catechol or hydroquinone. The hydroxyl radicals may also attack the two positions of p-benzoquinone, and generate 1, 2, 4-benzenetriol, 2, 5-dihydroxy-1, 4-benzoquinone, and acetic acid. During the reaction, MS analysis also suggested that there might be macromolecular substances such as acid anhydride or ester, and the specific formation process needs to be further studied. The final products of both these possible pathways are CO₂ and H₂O, as shown in Figure 6 [35].

Figure 6 presents the probable reaction pathway for the ozonation degradation of phenol, highlighting the stepwise oxidative transformations mediated by ozone (O₃) and hydroxyl radicals (•OH). The process initiates with the electrophilic attack of ozone and/or •OH on the phenol molecule, leading to hydroxylation of the aromatic ring to form catechol, hydroquinone, and resorcinol as primary dihydroxybenzene isomers. These intermediates are susceptible to further hydroxylation, oxidation, and ring-cleavage reactions due to the high reactivity of the ozonation products, particularly in aqueous environments where •OH radicals are generated from ozone decomposition. Following dihydroxylation, the aromatic ring undergoes cleavage to form open-chain dicarboxylic acids such as muconic acid, which signifies a critical transition from aromatic to aliphatic structures. Muconic acid and its isomers undergo successive decarboxylation and hydroxyl radical-induced oxidation to yield smaller carboxylic acids, including maleic acid, fumaric acid, and eventually oxalic acid, formic acid, and acetic acid. These low-molecular-weight acids represent the terminal products prior to full mineralization. The final oxidative steps involve the breakdown of these acids to carbon dioxide (CO₂) and water (H₂O), completing the mineralization process. This pathway underscores the efficiency of ozone-based advanced oxidation processes (AOPs) in degrading phenolic pollutants through a combination of direct ozone attack and indirect oxidation by hydroxyl radicals. The multiple oxidation and ring-opening steps highlight the transformation of persistent aromatic compounds into environmentally benign end products. The sequence also reflects the importance of both electrophilic substitution and radical-driven mechanisms in ozone-induced phenol degradation.

3.3. Photocatalysis

Photocatalysis involves the use of both a catalyst and light energy to generate highly reactive species that can degrade organic pollutants [36,37,38]. The catalyst, usually a semiconductor material such as titanium dioxide (TiO₂) or zinc oxide (ZnO), absorbs photons and creates electron–hole pairs. These charge carriers then participate in redox reactions, leading to the degradation of pollutants. The underlying mechanism includes the generation of hydroxyl radicals (${}^{•}OH$) through reactions between the catalyst and species like water or oxygen [38,39,40]. A prerequisite for initiating a photocatalytic reaction is that the energy imparted by photons onto the photocatalyst surpasses the energy gap (approximately 3.2 eV for titanium dioxide) between the valence band (VB) and the conduction band (CB). Upon absorption of light energy equal to or exceeding 3.2 eV, electrons residing in the VB transition to the CB, resulting in the generation of photogenerated electrons (CB-e⁻) while leaving behind corresponding holes in the VB (VB-h⁺) (Equation (7)). In the presence of moisture in the ambient air, photogenerated electrons (CB-e⁻) and holes (VB-h⁺) interact with oxygen and water molecules, respectively. Photogenerated electrons (CB-e⁻) exhibit strong reducibility, facilitating the reduction of surface-bound oxygen molecules to superoxide free radicals ($•O_2^{-}$), which subsequently undergo a cascade of reactions leading to the formation of hydroxyl radicals (•OH) (Equations (8)–(10)). Conversely, the VB holes (VB-h⁺) possess robust oxidation potential, enabling the oxidation of hydroxide ions (−OH) (including those within water molecules) to generate free hydroxyl radicals (${}^{•}OH$) simultaneously (Equations (11) and (12)) [41,42]. The hydroxyl radical (${}^{•}OH$) emerges as the principal oxidant in the photocatalytic oxidative degradation of organic pollutants, owing to its formidable oxidation capabilities.

$$\mathrm{T}\mathrm{i}{\mathrm{O}}_2+\mathrm{h}\mathrm{v}\to {\mathrm{e}}^{-}+\mathrm{T}\mathrm{i}{\mathrm{O}}_2\left({\mathrm{h}}^{+}\right)$$

(7)

$$\mathrm{n}\mathrm{T}\mathrm{i}{\mathrm{O}}_2\left({\mathrm{e}}^{-}\right)+{\mathrm{O}}_2\to \mathrm{n}\mathrm{T}\mathrm{i}{\mathrm{O}}_2+•{\mathrm{O}}_2^{-}$$

(8)

$$Ti{O}_2\left(e^{-}\right)+O_2+2H_{2}O\to Ti{O}_2+H_2{O}_2+2{OH}^{-}$$

(9)

$$Ti{O}_2\left(e^{-}\right)+H_2{O}_2\to Ti{O}_2+{}^{•}OH+{OH}^{-}$$

(10)

$$Ti{O}_2\left(h^{+}\right)+H_{2}O\to Ti{O}_2+H^{+}+{}^{•}OH$$

(11)

$$Ti{O}_2\left(h^{+}\right)+{OH}^{-}\to Ti{O}_2+{}^{•}OH$$

(12)

Traditional photocatalysts such as titanium dioxide (TiO₂) have been widely employed for the photodegradation of pesticide pollutants in water due to their strong oxidizing potential, chemical stability, and non-toxicity. However, TiO₂ exhibits significant limitations, particularly its wide bandgap (~3.2 eV for anatase), which restricts its activation to UV light (<387 nm), accounting for only about 5% of the solar spectrum. This limits its overall photocatalytic efficiency under natural sunlight. Moreover, TiO₂ can suffer from rapid electron–hole recombination, reducing its degradation performance over time [43,44].

To overcome these drawbacks, advanced photocatalysts have been developed, including doped semiconductors (e.g., N-doped TiO₂), composite materials (e.g., TiO₂/graphene, ZnO/CdS), and visible-light-active photocatalysts such as bismuth-based compounds (e.g., BiVO₄, Bi₂WO₆) and graphitic carbon nitride (g-C₃N₄). These materials exhibit narrower bandgaps, enabling activation under visible light (400–700 nm), which constitutes a larger portion of the solar spectrum. Additionally, heterojunctions and co-catalyst loading strategies have been shown to enhance charge separation, thereby improving photocatalytic efficiency and long-term stability during continuous operation in aqueous environments [45,46]. When exposed to radiation, photocatalysts become activated, generating highly reactive photo-induced charge carriers that interact with pollutants, as depicted in Figure 7. This process allows for the efficient removal of pollutants at ambient temperature and pressure, offering a solution to the high energy consumption typically associated with conventional methods.

3.4. UV/H₂O₂ Process

UV/H₂O₂ has demonstrated efficacy in degrading macromolecular organic pollutants in water, leading to the formation of smaller molecule organic species [47,48]. This process exhibits notable removal efficiency towards fluorescent compounds, substances containing benzene rings, or those with double bonds owing to the formation of high-redox-potential hydroxyl radicals (Equation (13)) [47,49]. The UV/H₂O₂ process employs three main degradation mechanisms: firstly, hydrogen peroxide’s strong oxidizing properties enable direct oxidation of organic compounds in water. Secondly, UV irradiation initiates molecular bond dissociation, leading to the breakdown of organic pollutants. Thirdly, under UV irradiation, hydrogen peroxide undergoes photolysis, generating hydroxyl radicals (${}^{•}OH$) that are instrumental in oxidizing and decomposing organic pollutants. This oxidation facilitated by hydroxyl radicals constitutes the primary reaction pathway in the UV/H₂O₂ process.

$${\mathrm{H}}_2{\mathrm{O}}_2+\mathrm{h}\mathrm{v}(\mathsf{\lambda }=250~254\mathrm{n}\mathrm{m})\to 2{}^{•}\mathrm{O}\mathrm{H}$$

(13)

Hydroxyl radicals (${}^{•}OH$) initiate their attack on the carbaryl molecule, causing the disruption of chemical bonds within carbaryl. This reaction can also result in the hydroxylation of the carbaryl molecule, incorporating hydroxyl groups (OH−) into its structure. As a consequence, subsequent reactions may lead to the breakdown of the carbaryl ring, fragmenting the compound into smaller components and generating intermediate compounds. These intermediates, including hydroxylated carbaryl derivatives and other by-products, are formed throughout the degradation process [50]. Further oxidation and decomposition reactions, facilitated by hydroxyl radicals (·OH), proceed to break down complex structures into simpler, more readily mineralized compounds. The degradation sequence progresses until complete mineralization of carbaryl is achieved, yielding non-toxic inorganic end products such as carbon dioxide (CO₂) and water. The monitoring of by-products formed during the degradation process remains essential to validate the efficiency and safety of the treatment [50]. In Figure 8, the assessment of carbaryl elimination utilizing UV and UV/H₂O₂ processes was explored. It became evident that the use of UV alone without H₂O₂ for carbaryl removal exhibited minimal effectiveness. Conversely, the combination of UV irradiation with H₂O₂ significantly hastened the elimination process, resulting in complete degradation within 75 min, attributed to the heightened generation of hydroxyl radicals facilitated by H₂O₂. The postulated pathway mechanism was based on the analysis of aromatic intermediates, carboxylic acids, and anions through GC-MS and IC techniques. Key indicators supporting carbaryl decomposition by UV/H₂O₂ included variations in dissolved oxygen levels, pH, acidity concentrations, and formaldehyde presence. The results underscore that carbaryl pesticides are effectively degraded through UV and UV/H₂O₂ processes, highlighting the potential of this approach for pesticide removal in drinking water and wastewater treatment applications.

The degradation pathway of carbaryl (1-naphthyl-N-methylcarbamate) under the UV/H₂O₂ AOP is illustrated in Figure 8, highlighting a series of oxidative transformations driven by hydroxyl radicals (•OH). Upon exposure to UV irradiation, hydrogen peroxide decomposes to generate reactive •OH species, which initiate the degradation of the carbaryl molecule through electrophilic attack on the aromatic and carbamate functional groups. The initial steps involve hydroxylation, N-dealkylation, and cleavage of the carbamate moiety, forming a series of hydroxylated and restructured aromatic compounds such as 3-(2-ethylamino)-1-hydroxyethylphenol,(E)-1-phenyl-2-ynylbut-2-en-1-ol, and(Z)-2-(hydroxyimino)-3-phenylpropanoic acid. These intermediates reflect the diversity of oxidative attack points and radical-driven rearrangements occurring in the early stages of the process.

Subsequent transformations involve progressive breakdown of the naphthalene ring, generating hydroxylated monoaromatic derivatives such as naphthalen-1-ol and naphthalen-2-ol, as well as dicarboxylic acids like phthalic acid, indicative of ring-opening oxidation. These aromatic intermediates are further mineralized into low-molecular-weight aliphatic acids, including citric acid and malic acid, which signal partial mineralization of the original compound. Continued oxidation leads to the formation of simpler compounds such as formic acid, acetic acid, and oxalic acid, representing the final stages of carbon backbone cleavage. Ultimately, these are mineralized to carbon dioxide and water, confirming the efficacy of the UV/H₂O₂ process in achieving complete degradation and detoxification of carbaryl. This pathway highlights the capability of UV/H₂O₂ treatment to dismantle complex pesticide structures through a cascade of hydroxyl radical-mediated reactions.

3.5. UV/O₃ Process

The UV/O₃ process represents an advanced photochemical oxidation method where ozone and ultraviolet radiation are introduced simultaneously. This approach capitalizes on ozone’s oxidative properties and ultraviolet light’s photolytic capabilities, utilizing the active species generated from ozone decomposition under ultraviolet light to oxidize organic matter. Glaze et al. outlined the synergistic mechanisms between ultraviolet light and ozone (Equations (14)–(17)) [51]. Ozone (O₃) undergoes photolysis under UV radiation, resulting in the production of hydrogen peroxide (H₂O₂). Subsequently, hydrogen peroxide reacts with ozone to generate hydroxyl radicals (${}^{•}OH$), a process known as the peroxone process. Additionally, hydrogen peroxide can independently produce hydroxyl radicals (${}^{•}OH$) under UV radiation.

$$O_3+{OH}^{-}\to {}^{•}OH$$

(14)

$$O_3+H_{2}O\stackrel{hv}{\to }{H_{2}O}_2$$

(15)

$$O_3+{H_{2}O}_2\to {}^{•}OH$$

(16)

$${H_{2}O}_2\stackrel{hv}{\to }{}^{•}OH$$

(17)

In the combination of ultraviolet and ozone, another active species, ${HO}_2•$, is generated, which significantly contributes to the degradation of organic pollutants in water [52]. An outstanding advantage of this combined process is its ability to promote the indirect reaction of ozone and facilitate the transformation of organic compounds from ground-state molecules to active species. This creates favorable conditions for the oxidation of organic compounds, thereby enhancing their degradation efficiency.

3.6. Electrochemical Oxidation

Electrochemical oxidation involves the application of electrical energy to drive the oxidation of pollutants in an aqueous solution, resulting in their breakdown into less harmful substances. In AOPs, reactive species, primarily hydroxyl radicals (•OH), are generated, which are powerful oxidizers capable of decomposing a wide range of organic contaminants [53]. Figure 9 illustrates the mechanism of electrochemical degradation of organic pollutants using both non-active and active anodes.

4. Relationship Between Sustainability and AOPs for Pesticide Degradation

AOPs are increasingly recognized for their eco-friendly approach to degrading pesticide pollutants in water. These processes generate highly reactive oxidative species such as hydroxyl radicals (•OH), sulfate radicals (SO₄•⁻), and superoxide (O₂•⁻), which are capable of mineralizing complex pesticide molecules into benign end-products like carbon dioxide (CO₂), water (H₂O), and inorganic ions. This complete mineralization significantly reduces the formation of toxic intermediates, a notable improvement over conventional treatment methods like chlorination, which may produce harmful disinfection by-products [54]. In terms of energy and resource efficiency, many AOP technologies such as photocatalysis (e.g., TiO₂/UV), electrochemical oxidation, and ozonation are undergoing optimization to reduce their energy and reagent demands. This transition enhances their sustainability by lowering the overall carbon footprint and operational costs. Particularly promising are solar-driven systems and AOPs powered by renewable electricity sources, which align with global goals for green energy integration in water treatment [55]. Another major advantage of AOPs is their potential to minimize secondary pollution. For example, electrochemical AOPs such as electro-Fenton and electro-ozone systems rely on in situ generation of powerful oxidants like hydrogen peroxide (H₂O₂) and ozone (O₃), eliminating the need for external chemical additions. This feature greatly reduces chemical residue and sludge formation, offering a cleaner alternative to traditional oxidation methods that often generate environmentally burdensome waste streams [20].

AOPs also play a critical role in enabling circular water systems. Their effectiveness in achieving near-complete degradation of trace-level pesticides allows them to be seamlessly integrated into water recycling and reuse infrastructures. This capability is particularly vital in agriculture and industry, where water reuse is essential for sustainability under conditions of increasing water scarcity. In alignment with green chemistry principles, recent developments in AOPs emphasize the use of environmentally friendly catalysts and materials. These include biodegradable catalysts, biochar, and nanomaterials synthesized through green routes. By reducing dependence on rare, expensive, or potentially toxic substances, these innovations support a circular economy model in water treatment technologies [56]. Finally, the cost-effectiveness and scalability of AOP technologies are rapidly improving. Emerging systems like solar-activated peroxides, persulfate activation, and photo-electrochemical cells are being engineered for economic feasibility and large-scale deployment. This trend enhances sustainability by promoting broader and more equitable access to safe water treatment solutions, particularly in low- and middle-income regions where cost remains a critical barrier.

5. Pesticide Classification, Chemical Diversity, and Structure–Reactivity Relationships in AOPs

Pesticides are broadly classified based on their target organisms, with major categories including insecticides (targeting insects), herbicides (targeting weeds), fungicides (targeting fungi), rodenticides (targeting rodents), and algaecides (targeting algae) [57]. Each class encompasses a wide array of chemical structures, ranging from simple organic molecules to complex heterocyclic systems. For instance, insecticides like organophosphates (e.g., chlorpyrifos) and pyrethroids (e.g., permethrin) are structurally distinct from herbicides such as phenoxy acids (e.g., 2,4-D) or triazines (e.g., atrazine). This chemical diversity significantly influences their environmental behavior, persistence, and susceptibility to degradation processes.

Since AOPs rely on the generation of highly reactive species like hydroxyl radicals (•OH) and sulfate radicals (SO₄•⁻), the effectiveness of AOPs is strongly determined by the chemical structure of the pesticide. Compounds containing electron-rich aromatic rings, double bonds, or heteroatoms (such as nitrogen, sulfur, or phosphorus) typically exhibit higher reactivity toward oxidation [54]. For example, pesticides with activated aromatic systems or functional groups like amines, hydroxyls, and phenols are more readily attacked by radicals. In contrast, pesticides with strong electron-withdrawing groups (e.g., halogens in polychlorinated pesticides) or sterically hindered structures may resist oxidation, requiring more aggressive AOP conditions (higher oxidant doses, longer reaction times).

The structure–reactivity relationship is critical in designing and optimizing AOP treatments for pesticide-contaminated waters. Understanding molecular descriptors such as electron density, bond dissociation energy (BDE), and HOMO (highest occupied molecular orbital) energy levels helps predict degradation pathways and rates [58]. For instance, pesticides with lower BDE for C–H or C–Cl bonds are generally more susceptible to radical attack. Moreover, quantitative structure–activity relationship (QSAR) models have increasingly been used to forecast AOP effectiveness against diverse pesticide structures, guiding the selection of the most appropriate oxidation technology and operating parameters. Thus, integrating knowledge of pesticide chemical diversity with structure–reactivity principles enhances both the efficacy and sustainability of AOP applications in environmental remediation.

6. Advantages and Limitations of Advanced Oxidation Processes in the Dechlorination of Pesticide Pollutants

Table 1. Comparisons of different AOPs based on their advantages and limitations in the dechlorination of pesticide pollutants.

Advanced Oxidation Process (AOPs)	Advantages	Limitations	References
Photocatalysis	- Broad applicability: Photocatalysis can effectively degrade a wide range of pesticides, including various chemical classes. - High degradation efficiency: The generation of highly reactive hydroxyl radicals (·OH) through photocatalysis enables efficient and complete pesticide degradation. - Regeneration of catalyst: Catalyst materials like TiO2 or ZnO can be regenerated and reused, leading to cost savings.	- Catalyst selectivity: Not all pesticides can be efficiently degraded by photocatalysis, as the process’s effectiveness depends on the pesticide’s adsorption and reaction properties. - Light dependency: Photocatalytic reactions require a light source, preferably ultraviolet (UV) radiation. This dependency may limit operation under certain conditions and increase energy consumption. - Catalyst recovery and recycling challenges: Separating the catalyst from the treated water or waste stream can be challenging, affecting the overall efficiency and practicality of photocatalysis.	[60,61]
Ozonation process	- Wide pesticide applicability: Ozone is highly reactive and effective in degrading various pesticide classes, including herbicides, insecticides, and fungicides. - Rapid reaction kinetics: Ozonation offers fast reaction rates, resulting in relatively quick degradation of pesticides. - No chemical byproduct formation: Ozone decomposes into oxygen, leaving no harmful residues or additional chemical pollutants.	- Limited persistence: Ozone has a short half-life and readily decomposes. Therefore, its effective contact time with the pesticide may be limited and require continuous ozone generation for sustained degradation. - Selectivity: While ozone can degrade many pesticides, there may be variations in reactivity, and some pesticides might require longer contact times or higher ozone concentrations. - Off-gas management: The removal and treatment of ozone-rich off-gases can be challenging, requiring appropriate air pollution control measures.	[62,63]
Fenton process	- Effective for complex matrices: Fenton’s reaction can efficiently degrade pesticides even in complex matrices like wastewater or soil samples, where other treatments may encounter difficulties. - Wide pH range: The Fenton reaction can operate under a wide pH range, allowing flexibility in treating different environmental conditions. - High reactivity: Fenton’s reaction generates highly reactive hydroxyl radicals, leading to rapid and effective degradation of pesticides. - Efficient in acidic conditions (pH 3–4). - Cost-effective compared to other AOPs	- Catalyst limitations: Selecting the proper iron catalyst and maintaining its activity is crucial. Iron catalysts may lose efficiency over time due to precipitation, fouling, or other factors, necessitating replacement or regeneration. - Hydrogen peroxide requirement: The Fenton’s reaction relies on the addition of hydrogen peroxide, which can be costly and pose safety concerns in large-scale applications. - pH adjustment: Fenton’s reaction often requires pH adjustment to initiate the reaction. This step adds complexity to the process and might limit its application in some scenarios.	[64]
UV/H2O2	- UV/H2O2 is effective in degrading many pesticide classes and complex mixtures. - It offers relatively fast reaction rates and can achieve high degradation efficiencies. - The process can be easily controlled by adjusting the dosages of UV light and hydrogen peroxide. - No sludge production, and H2O2 decomposes into water and oxygen.	- UV/H2O2 requires a sufficient supply of hydrogen peroxide, which can add to the operational costs. - The presence of certain water constituents can inhibit or compete with the reaction, reducing overall efficiency. - UV/H2O2 may not be suitable for treating large volumes of water due to the limited penetration depth of UV light.	[65]
Sonochemical degradation	- Efficiency: Sonochemical degradation can achieve high levels of pollutant degradation due to the intense cavitation and localized hotspots created by ultrasound waves. - Versatility: It can be applied to a wide range of pollutants, including organic compounds, pesticides, and pharmaceuticals. - Green process: Sonochemical degradation is generally considered a green process as it operates at ambient temperatures and pressures, reducing energy consumption.	- Energy-intensive: Sonochemical degradation requires high-power ultrasound waves, making it an energy-intensive process. - Limited scalability: Sonochemical reactors for large-scale applications can be challenging due to issues such as uneven distribution of cavitation and scale-up complexities.	[66]
Electrochemical oxidation	- Selectivity: Electrochemical oxidation allows for selective degradation of specific pollutants, depending on the choice of electrode material and operating conditions. - Continuous operation: It enables continuous pollutant removal as long as a sufficient supply of electricity is available. - Easy control: Parameters such as current density and electrode potential can be adjusted to optimize the degradation process. - No chemical addition is needed.	- Electrode fouling: Fouling of the electrodes can occur during the electrochemical oxidation process, reducing its efficiency. - Limited applicability: Electrochemical oxidation may not be suitable for certain types of pollutants that are less amenable to oxidation or require specific reaction pathways. - Cost: The cost associated with electrical power consumption, electrode maintenance, and system setup can be a limitation.	[5,67]
Advanced oxidation with peroxides	- Versatility: Advanced oxidation with peroxides can effectively degrade a wide range of organic pollutants, including hard-to-treat compounds. - Simplicity: Peroxide-based AOPs often have straightforward reactor designs, making them easier to implement and operate. - No need for external energy: In certain cases, the reactions involving peroxides can be initiated by natural light rather than requiring additional energy sources.	- Cost: The use of peroxides in AOPs can contribute to higher operational costs due to the procurement and handling of reagents. - By-products formation: Depending on the reaction conditions, some AOPs involving peroxides can produce undesired by-products, which need further treatment or disposal. - pH sensitivity: The effectiveness of peroxide-based AOPs can be pH-dependent, and optimizing the reaction conditions may be necessary to achieve optimal degradation efficiency.	[68,69]

compares the advantages and limitations of different AOPs in the dechlorination of pesticide pollutants. AOPs offer significant advantages for the dechlorination of pesticide pollutants, including high efficacy in breaking down recalcitrant chlorinated compounds (e.g., DDT, chlorpyrifos) via hydroxyl radicals (•OH) that cleave C–Cl bonds, often achieving >90% dechlorination and mineralization to CO₂, H₂O, and Cl⁻ ions. AOPs like UV/H₂O₂, photocatalysis, and plasma treatment operate at ambient conditions, avoid sludge generation, and can be tailored to target specific pollutants (e.g., selective dechlorination of atrazine). However, limitations include high energy and chemical inputs (e.g., H₂O₂, UV lamps), formation of toxic intermediates (e.g., chlorinated byproducts from incomplete degradation), and pH dependence (e.g., Fenton’s reagent requires acidic conditions). Scalability remains challenging due to cost and complexity, necessitating hybrid systems (e.g., sonoelectrolysis) for sustainable implementation [59].

7. Studies on Pesticide Treatment in Aqueous Environment Using AOPs

Table 2. Categorization of the studies based on the type of pesticide, AOP utilized, and their key findings.

Studies	AOPs Method	Target Pesticide	Key Findings	References
Photocatalytic degradation of atrazine using TiO2	Photocatalysis (TiO2/UV)	Atrazine	95% degradation under UV in 120 min	[70]
Advanced oxidation of chlorpyrifos by Fenton’s reagent	Fenton (Fe2+/H2O2)	Chlorpyrifos	98% degradation at pH 3 in 30 min	[49]
Ozonation of imidacloprid in aqueous solutions	Ozonation (O3/H2O2)	Imidacloprid	90% removal in 20 min (O3 dose: 5 mg/L)	[71]
Anodic oxidation of glyphosate on BDD electrodes	Electrochemical (BDD)	Glyphosate	>90% TOC removal at 100 mA/cm2 in 4 h	[72]
The effect of UV/H2O2 treatment on disinfection by-product formation potential under simulated distribution system conditions	UV/H2O2	Atrazine	80% degradation	[73]
Mechanism and kinetics of parathion degradation under ultrasonic irradiation	Sonochemical	parathion	85% degradation	[74]

summarizes recent studies on pesticide degradation using AOPs, demonstrating their versatility and efficiency across diverse contaminants. For instance, TiO₂ photocatalysis achieved 95% degradation of atrazine under UV light in 120 min, while the Fenton process rapidly degraded 98% of chlorpyrifos within 30 min at pH 3, leveraging hydroxyl radicals for efficient oxidation. Ozonation (O₃/H₂O₂) showed 90% removal of imidacloprid in just 20 min, though its reliance on ozone dosing may limit scalability. Electrochemical oxidation using boron-doped diamond (BDD) electrodes achieved >90% total organic carbon (TOC) removal for glyphosate, highlighting its potential for complete mineralization, albeit with higher energy demands. Complementary studies on UV/H₂O₂ (80% atrazine degradation) and sonochemical processes (85% parathion degradation) further underscore the adaptability of AOPs to different pesticide classes, though challenges such as energy costs, byproduct formation, and process-specific limitations (e.g., pH dependence for Fenton) must be addressed for large-scale applications. Collectively, these studies illustrate the promise of AOPs while emphasizing the need for tailored solutions based on pollutant characteristics and operational constraints.

8. Factors Influencing Pesticide Degradation in Aqueous Environment

The efficiency of AOPs is strongly influenced by the pH of the reaction medium, with different pesticides showing varying degradation rates at different pH levels. Optimization and adjustment of pH to suit the specific AOPs and pesticides are crucial for maximum efficiency [9,75]. Temperature is another critical factor affecting AOPs efficiency, as higher temperatures generally enhance reaction rates by increasing kinetic energy. However, extremes in temperature can impact the stability of catalysts or reactants, necessitating the maintenance of an appropriate temperature range [7,76]. Catalysts play a key role in AOPs by improving reaction rates and selectivity. The selection of suitable catalysts compatible with both the pesticide and AOP system significantly influences overall efficiency. Furthermore, the duration of AOP treatment, initial pesticide concentration, and presence of other substances in the matrix can all affect degradation efficiency [75,77]. Optimizing reaction time, considering initial pesticide concentrations, and understanding the impact of coexisting substances are essential for effective pesticide degradation processes. It is worth noting that the impact and optimal conditions of these factors can vary depending on the specific pesticide, AOP method, and environmental conditions. Therefore, conducting preliminary investigations and optimization studies considering these factors is crucial to ensure effective pesticide treatment using AOPs.

The efficiency of AOPs in degrading pesticides in aqueous environments is influenced by multiple interdependent factors, as demonstrated by specific studies. For instance, pH plays a critical role, with the Fenton process achieving 98% degradation of chlorpyrifos at pH 3 but dropping below 50% at higher pH due to Fe²⁺ precipitation [78]. The oxidant dosage must be carefully balanced, as excessive H₂O₂ (>100 mg/L) can quench hydroxyl radicals, reducing atrazine degradation from 95% to 60% [79]. The water matrix also significantly impacts outcomes; natural organic matter (NOM) scavenges radicals, lowering glyphosate degradation by 30% in river water compared to ultrapure water, while inorganic ions like Cl⁻ hinder sonochemical degradation of parathion by 20% [80]. Temperature and catalyst selection further modulate efficiency, as seen in electro-Fenton systems where 2,4-D degradation improved from 70% to 90% at 40 °C [81], and boron-doped diamond (BDD) electrodes outperformed Pt electrodes in mineralizing glyphosate due to higher •OH yields [82]. Additionally, the initial pesticide concentration affects radical availability, with chlorpyrifos degradation declining from 95% (1 ppm) to 60% (10 ppm) in UV/persulfate systems. These examples underscore the need for tailored AOP optimization to address variable conditions and ensure effective pesticide removal while minimizing energy and chemical costs.

Table 3. A synthesis table summarizing each AOP’s strengths, weaknesses, appropriate conditions, and targeted pesticide types.

AOP Type	Strengths	Weaknesses	Optimal Conditions	Type of Pollutant and Reference
UV/H2O2	Simple setup, strong •OH generation, no catalyst needed	UV dependency, H2O2 cost and instability, limited sunlight use	Low pH (~3–4), UV source required	Phenoxy herbicides (e.g., 2,4-D), atrazine [83]
O3 (Ozonation)	Strong oxidant, can decompose into •OH under alkaline pH	Limited mineralization, pH-sensitive, ozone instability	Alkaline pH (>8), pre-oxidation step often required	Carbamates, organophosphates, simazine [84]
Photo-Fenton (UV/Fe2+/H2O2)	Cost-effective, works well under UV, high •OH yield	Narrow optimal pH (~2.5–3.5), iron sludge formation	Acidic pH, UV-A or solar radiation	Chlorinated pesticides, 2,4-D, diuron [85]
TiO2 Photocatalysis (UV)	Stable, reusable, effective under UV	UV-only activation, electron–hole recombination	UV light required, slightly acidic to neutral pH	Atrazine, paraquat, chlorpyrifos [26]
Visible-light Photocatalysis (g-C3N4, BiVO4)	Solar-driven, tunable bandgap materials	Often lower efficiency than UV systems, stability issues	Visible light, neutral pH	Broad-spectrum degradation: triazines, phenylureas [20]
Electrochemical AOPs (EAOPs)	No chemicals needed, controllable via voltage, scalable	High energy cost, electrode degradation	Conductive water, optimized current density	Persistent pollutants like glyphosate, 2,4-D, pesticides with halogens [83]

summaraized different AOPs strengths, weaknesses, appropriate conditions, and targeted pesticide types.

When and Why a Hybrid AOP System Is Preferable over Standalone Systems

Hybrid AOPs are preferable over standalone systems when the target pollutants exhibit high chemical stability, low reactivity toward single oxidants, or when the water matrix contains scavengers that hinder radical activity. Standalone AOPs, such as UV/H₂O₂ or ozonation, often face limitations such as narrow pH operating ranges, incomplete mineralization, or inefficient generation of reactive oxygen species (ROS) under natural light. In contrast, hybrid systems—such as UV/O₃, photo-Fenton, or electro-Fenton—synergistically combine the strengths of individual AOPs, enhancing hydroxyl radical (•OH) generation and promoting more efficient degradation of recalcitrant compounds. For instance, the UV/O₃ process benefits from both direct ozone oxidation and UV-induced radical pathways, significantly improving pesticide removal compared to UV or ozone alone [83]. Similarly, the electro-Fenton process offers continuous in situ production of H₂O₂ and regeneration of Fe²⁺ at the cathode, enabling high and sustained mineralization of persistent herbicides like atrazine or 2,4-D under mild conditions [85]. Hybrid AOPs are especially valuable in real water matrices (e.g., wastewater or agricultural runoff) where natural organic matter and ions can interfere with oxidant performance. By enhancing ROS yield, reducing treatment time, and broadening operational flexibility, hybrid systems provide a more robust and cost-effective solution for treating complex pesticide mixtures in aqueous environments [20].

9. The Current Challenges and Limitations Faced in the Application of AOPs for Pesticide Treatment in Aqueous Environment and Future Directions

The implementation of AOPs for pesticide remediation presents several noteworthy challenges and limitations. To begin with, the diverse chemical compositions of pesticides lead to varying degradation rates and pathways when exposed to AOPs. This variability complicates the development of effective treatment methods, requiring tailored strategies for individual pesticides, thereby augmenting the intricacy and cost of the treatment process [86]. AOPs often rely on high-energy sources like UV radiation, ozone, or hydrogen peroxide, which can be demanding in terms of resources and expenses, especially when considering large-scale applications. The generation of potentially harmful by-products during AOP treatment raises alarming concerns regarding water quality and environmental repercussions, compelling the necessity of thorough monitoring and mitigation measures. The efficacy of AOPs is susceptible to water quality factors such as pH, temperature, and the presence of assorted organic and inorganic components, further complicating their practical implementation in real-world treatment scenarios [87].

The application of AOPs for pesticide treatment is an evolving field that offers promising future directions. One key direction is the development of more efficient and cost-effective AOPs tailored specifically for different types of pesticides. Future research efforts may focus on enhancing the selectivity and effectiveness of AOPs to target a wider range of pesticides with improved degradation rates and pathways. There is a growing emphasis on developing integrated treatment approaches that combine AOPs with other innovative technologies to enhance pesticide removal efficiency while minimizing the formation of harmful by-products. Moreover, future directions in AOPs for pesticide treatment may involve the optimization of operating conditions, such as pH, temperature, and reactor design, to ensure consistently high treatment performance and scalability from lab-scale to field-scale applications. Continuous advancements in AOP technology, including the use of alternative energy sources and novel catalyst materials, can further enhance the sustainability and practicality of AOPs for pesticide treatment [88].

Despite their efficacy, AOPs face significant challenges in large-scale pesticide treatment. A key limitation is high operational costs, exemplified by UV/H₂O₂ systems requiring expensive UV lamps and continuous H₂O₂ dosing, with energy demands reaching 50–100 kWh/m³ for complete atrazine mineralization. Toxic byproduct formation further complicates implementation; for instance, ozonation of imidacloprid generates carcinogenic nitrosamines, while incomplete degradation of chlorpyrifos via photocatalysis yields more persistent chlorinated intermediates. Matrix interference (e.g., NOM scavenging radicals in natural waters) reduces glyphosate degradation efficiency by 30–50%, and pH sensitivity limits Fenton applications to acidic conditions. Future research is directed toward the development of hybrid systems—such as solar-driven photocatalysis combined with electro-Fenton processes—to minimize energy consumption. Advances in catalytic ozonation using doped nanomaterials are also gaining attention for their potential to reduce the formation of harmful byproducts. Additionally, artificial intelligence is increasingly being integrated to optimize operational parameters for complex, real-world water matrices. Emerging scalable and energy-efficient AOPs, including non-thermal plasma and piezoelectric catalysis, are showing promise in overcoming current technological and economic barriers.

10. Conclusions

Advanced oxidation processes have proven highly effective in degrading diverse pesticides, consistently reducing their concentrations below regulatory limits. Among the tested methods, UV/H₂O₂ and UV/O₃ systems demonstrated superior degradation rates compared to standalone ozone or UV treatments. Comparative studies of AOPs, such as UV, ozone, and the combined UV/O₃ approach revealed that hybrid methods outperform individual techniques, emphasizing the value of synergistic oxidation strategies. Key operational parameters, including pH, temperature, reaction duration, initial pesticide concentration, and catalyst choice, significantly influence degradation efficiency. These factors exhibit variable impacts depending on pesticide properties and reaction conditions, underscoring the need for meticulous optimization of AOP parameters to maximize performance.

While AOPs offer notable advantages, such as broad applicability, rapid kinetics, high degradation efficiency, and catalyst reusability, challenges persist. Limitations include reliance on light sources, treatment selectivity, transient effects, catalyst constraints, and operational costs. Addressing these drawbacks is critical for scalable and sustainable implementation. Future research should prioritize three areas: (1) catalyst innovation: developing selective, stable catalysts through novel materials (e.g., nanostructured composites, catalytic coatings) and mechanistic studies on pesticide-catalyst interactions. (2) Parameter optimization: investigating how pH, oxidant concentration, irradiation intensity, and sequential/simultaneous treatment modes affect degradation pathways and by-product formation. (3) Sustainability enhancements: reducing energy consumption and costs while improving long-term efficacy for real-world wastewater treatment scenarios.