The presence of dyes in water stream is a major environmental problem that affects aquatic and human life negatively. Therefore, it is essential to remove dye from wastewater before its discharge into the water bodies. In this study, Banyan (Ficus benghalensis, F. benghalensis) tree leaves, a low-cost biosorbent, were used to remove brilliant green (BG), a cationic dye, from an aqueous solution. Batch model experiments were carried out by varying operational parameters, such as initial concentration of dye solution, contact time, adsorbent dose, and pH of the solution, to obtain optimum conditions for removing BG dye. Under optimum conditions, maximum percent removal of 97.3% and adsorption capacity (Qe) value of 19.5 mg/g were achieved (at pH 8, adsorbent dose 0.05 g, dye concentration 50 ppm, and 60 min contact time). The Langmuir and Freundlich adsorption isotherms were applied to the experimental data. The linear fit value, R² of Freundlich adsorption isotherm, was 0.93, indicating its best fit to our experimental data. A kinetic study was also carried out by implementing the pseudo-first-order and pseudo-second-order kinetic models. The adsorption of BG on the selected biosorbent follows pseudo-second-order kinetics (R² = 0.99), indicating that transfer of internal and external mass co-occurs. This study surfaces the excellent adsorption capacity of Banyan tree leaves to remove cationic BG dye from aqueous solutions, including tap water, river water, and filtered river water. Therefore, the selected biosorbent is a cost-effective and easily accessible approach for removing toxic dyes from industrial effluents and wastewater.

The removal of water pollutants by photocatalysis is a promising technique, mainly due to its environmentally friendly and sustainable nature. In this study, the degradation of a recalcitrant organic pollutant, malachite green (MG), was investigated in water by a microstructured silver oxide photocatalyst. The silver oxide (Ag₂O) microparticles (MPs) were synthesized by a low-cost, green method, mediated by green tea leaves extract. The surface, morphological and optical properties of the synthesized Ag₂O MPs were determined by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, X-ray diffraction (XRD) analysis, Fourier transform infrared (FTIR) spectroscopy, and ultraviolet-visible (UV-visible) spectrophotometry. The synthesized Ag₂O MPs showed good photoactivity, represented by 83% degradation of malachite green (MG) ([C]₀ = 0.4 mM, Ag₂O loading = 0.1 g L⁻¹) at neutral pH, in 3 h. Persulfate ions (PS) showed a strong synergistic effect on the efficiency of solar/Ag₂O photocatalysis, represented by complete MG removal in 15 min, in the presence of 1.6 mM PS. The results revealed that solar/Ag₂O, particularly solar/Ag₂O/PS photocatalysis is a promising method for the elimination of toxic organic pollutants, such as malachite green, from the water environment.

Diclofenac sodium was extensively used for treating arthritis, osteoarthritis and skeletal muscular injuries, which ultimately caused troubles for aquatic organisms as well as human beings. In this study, homogeneous catalytic advanced oxidation processes, including Fe²⁺/persulfate, Fe²⁺/peroxymonosulfate and Fe²⁺/H₂O₂, were used for the degradation of diclofenac sodium in water, without using UV-C light. About 89, 82 and 54% DCF sodium was decomposed by Fe²⁺/persulfate, Fe²⁺/peroxymonosulfate and Fe²⁺/H₂O₂, respectively, in 60 min. The degradation of diclofenac sodium followed the pseudo first-order kinetics, in all cases. The degradation efficiency of diclofenac sodium was significantly affected in the presence of various anions, such as NO₃⁻, HCO₃⁻ and SO₄²⁻. The mineralization studies revealed 62, 45 and 32% total carbon removal by Fe²⁺/persulfate, Fe²⁺/peroxymonosulfate and Fe²⁺/H₂O₂, respectively, in 60 min. In addition, the degradation byproducts of diclofenac sodium were determined by FTIR analysis. The results revealed that the Fe²⁺/oxidant system, particularly Fe²⁺/persulfate, was a promising technology for the elimination of toxic pharmaceuticals, such as diclofenac sodium, from the water environment.

Organochlorine pesticides (OCPs) have been used extensively as insecticides and herbicides. This study investigates the occurrence of lindane in surface water from the Peshawar valley (i.e., Peshawar, Charsadda, Nowshera, Mardan and Swabi districts of Khyber Pakhtunkhwa, Pakistan). Out of 75 samples tested (i.e., 15 samples from each district), 13 samples (including 2 from Peshawar, 3 from Charsadda, 4 from Nowshera, 1 from Mardan, and 3 from Swabi) are found to be contaminated with lindane. Overall, the detection frequency is 17.3%. The maximum concentration of lindane is detected in a water sample from Nowshera and found to be 2.60 μg L⁻¹. Furthermore, the degradation of lindane in the water sample from Nowshera, containing the maximum concentration, is investigated by simulated solar-light/TiO₂ (solar/TiO₂), solar/H₂O₂/TiO₂ and solar/persulfate/TiO₂ photocatalysis. The degradation of lindane by solar/TiO₂ photocatalysis is 25.77% after 10 h of irradiation. The efficiency of the solar/TiO₂ process is significantly increased in the presence of 500 μM H₂O₂ and 500 μM persulfate (PS) (separately), represented by 93.85 and 100.00% lindane removal, respectively. The degradation efficiency of lindane is lower in natural water samples as compared to Milli-Q water, attributed to water matrix effect. Moreover, the identification of degradation products (DPs) shows that lindane follows similar degradation pathways in natural water samples as the one in Milli-Q water. The results show that the occurrence of lindane in surface waters of Peshawar valley is a matter of great concern for human beings and the environment. Interestingly, H₂O₂ and PS assisted solar/TiO₂ photocatalysis is an effective method for the removal of lindane from natural water.

Natural water resources are severely exploited by the inevitable addition of emerging contaminants (ECs). ECs are newly identified synthetic or naturally occurring chemicals or biological agents that are released in the environment from various anthropogenic or natural sources. These contaminants, including pharmaceuticals and personal care products (PPCPs), pesticides, dyes, microplastics, per-and polyfluoroalkyl substances (PFAS), industrial chemicals or additives, nanomaterials and microcystin, are ubiquitous, toxic and persistent in the environment, and represent long-term and unpredictable threats to human beings and ecosystem (Shah et al., 2025). Many different techniques, including physical, biological and chemical methods are used for removal of ECs from water. Among them, advanced oxidation processes (AOPs) such as photocatalysis, Fenton, photo-Fenton, ionizing radiation, nonthermal plasmas, sonolysis, photolysis, electrochemical and ozonation have shown promising results in water treatment (Iqbal et al., 2024).Photocatalysis and UV-based AOPs have gained significant attention in water treatment, owing to the convenient and sustainable nature. Reaction mechanism is a useful tool in understanding the underlying principles of pollutant degradation. Evidence of reactive species generated during AOPs, as well as identification of degradation products provide enormous information on pollutants degradation pathways (Khan et al., 2024). The most common reactive species produced during AOPs include hydroxyl radicals, sulfate radicals, superoxide radical anions, and singlet oxygen. The hydroxyl and sulfate radicals react with organic compounds via addition, hydrogen abstraction and/or electron transfer mechanism. Kinetics studies are useful in evaluating process validity and optimization of reaction conditions in real-world environmental applications. The detection of emerging contaminants in various environmental samples is a growing research area in determining water quality-a desired parameter in water treatment.Biodegradation is an attractive research topic in recent years, owing to its cheap and environmentally friendly nature. Tremendous research is going on in developing novel, efficient and sustainable AOPs for water treatment and environmental remediation.Although AOPs are considered as very effective methods in the field of water purification, these methods face a number of challenges which need to be addressed and overcome to make these processes practically implemented. For example, many AOPs are costly due to the need of expensive reagents and oxidants, high energy consumption and reactor installation. These processes also face limited scalability, formation of toxic byproducts, and hindrance of their efficiency by different water constituents especially inorganic ions and organic matter. In photocatalysis, the photocatalyst recovery and leaching is the biggest hurdle in practical implementation of these processes.Fortunately, researchers are tirelessly trying to develop new strategies to overcome the limitations of AOPs. These strategies include the integration of AOPs with biological treatment methods for cost reduction, integration of different AOPs with each other for synergistic effects and efficiency enhancement, development of visible light active photocatalysts to fully utilize the renewable and freely available solar light, improving catalyst stability, recovery and reusability via film formation and magnetization, optimizing reactor design for better and effective mass transfer, and so on. In conclusion, this field is still open for researchers to utilize their specialized know-how, practical skills and expertise to develop newly integrated AOPs for long-term and large-scale applications at affordable cost.The research topic "Emerging trends in advanced oxidation processes for water treatment" of the special issue, contained four original research articles, expressing the presence of contaminants in environmental compartments and discussing new achievements in the field of AOPs for water treatment. These contributions cover the detection of an emerging pollutant-N-(1,3dimethylbutyl)-N′-phenyl p-phenylenediamine)-quinone (6PPD-quinone)-in the runoff water samples, the kinetics and mechanism of degradation of emerging contaminants by using more convenient and sustainable photocatalytic and UV-based AOPs, strategy for developing novel immobilized TiO2 photocatalyst using newly designed photoreactor for efficient removal of organic pollutant, and reusability potential of the photocatalysts.This collection features works that strengthen the sample preparation and analytical methods for emerging pollutant detection in water, the kinetics and mechanism of degradation of emerging contaminants by promising AOPs, i.e., UV/TiO2 photocatalysis, UV/H2O2, and UV/Fe 2+ /H2O2 processes, as well as biodegradation. The concentrations of a low quantity of a widely used and a model organic pollutant, 6-PPD-quinone, in the runoff water from different sources of Norway were detected. Meanwhile, the degradation of a mixture of four quinolone antibiotics of emerging concern, i.e., ofloxacin, norfloxacin, ciprofloxacin and enrofloxacin by biodegradation was investigated using mixed strain bacteria. i.e., 4-dimethylamino-benzophenone (DABP), 4-amino-benzophenone (ABP), and 4dimethylamino-phenol (DAP) (Figure 1). It was emphasized that proper focus should be given on removal of DPs, besides the removal of the target pollutants. Thus, UV/H2O2 and UV/H2O2/Fe 2+ were proved to be highly efficient methods for relieving the harmful environmental impacts of the dyes, such as malachite green. norfloxacin (NOR), ciprofloxacin (CIP) and enrofloxacin (ENR) by mixed strain bacteria. The strains were divided into two groups, i.e., in group mix and ENR, the resistant bacteria played the primary role of microorganisms and degrading bacteria had a secondary role, while in group mix and NOR, the...