Among the advanced oxidation processes (AOPs), the Fenton reaction has attracted much attention in recent years for the treatment of water and wastewater. This review provides insight into a particular variant of the process, where soluble Fe(II) salts are replaced by zero-valent iron (ZVI), and hydrogen peroxide (H₂O₂) is replaced by persulfate (S₂O₈²⁻). Heterogeneous Fenton with ZVI has the advantage of minimizing a major problem found with homogeneous Fenton. Indeed, the precipitation of Fe(III) at pH > 4 interferes with the recycling of Fe species and inhibits oxidation in homogeneous Fenton; in contrast, suspended ZVI as iron source is less sensitive to the increase of pH. Moreover, persulfate favors the production of sulfate radicals (SO₄^•−) that are more selective towards pollutant degradation, compared to the hydroxyl radicals (^•OH) produced in classic, H₂O₂-based Fenton. Higher selectivity means that degradation of SO₄^•−-reactive contaminants is less affected by interfering agents typically found in wastewater; however, the ability of SO₄^•− to oxidize H₂O/OH⁻ to ^•OH makes it difficult to obtain conditions where SO₄^•− is the only reactive species. Research results have shown that ZVI-Fenton with persulfate works best at acidic pH, but it is often possible to get reasonable degradation at pH values that are not too far from neutrality. Moreover, inorganic ions that are very common in water and wastewater (Cl⁻, HCO₃⁻, CO₃²⁻, NO₃⁻, NO₂⁻) can sometimes inhibit degradation by scavenging SO₄^•− and/or ^•OH, but in other cases they even enhance the process. Therefore, ZVI-Fenton with persulfate might perform unexpectedly well in some saline waters, although the possible formation of harmful by-products upon oxidation of the anions cannot be ruled out.

Glyphosate is a widely used herbicide, and it is an important environmental pollutant that can have adverse effects on human health. Therefore, remediation and reclamation of contaminated streams and aqueous environments polluted by glyphosate is currently a worldwide priority. Here, we show that the heterogeneous nZVI–Fenton process (nZVI + H₂O₂; nZVI: nanoscale zero-valent iron) can achieve the effective removal of glyphosate under different operational conditions. Removal of glyphosate can also take place in the presence of excess nZVI, without H₂O₂, but the high amount of nZVI needed to remove glyphosate from water matrices on its own would make the process very costly. Glyphosate removal via nZVI–-Fenton was investigated in the pH range of 3–6, with different H₂O₂ concentrations and nZVI loadings. We observed significant removal of glyphosate at pH values of 3 and 4; however, due to a loss in efficiency of Fenton systems with increasing pH values, glyphosate removal was no longer effective at pH values of 5 or 6. Glyphosate removal also occurred at pH values of 3 and 4 in tap water, despite the occurrence of several potentially interfering inorganic ions. Relatively low reagent costs, a limited increase in water conductivity (mostly due to pH adjustments before and after treatment), and low iron leaching make nZVI–Fenton treatment at pH 4 a promising technique for eliminating glyphosate from environmental aqueous matrices.

Fat, oil, and grease (FOGs) are a significant challenge for water management services. FOG in wastewater is generated by the increasing number of food service establishments (FSEs), as well as the pharmaceutical industry. It is estimated that approximately 30–40% of sewer clogs are caused by deposits of FOG in sewer pipes, which results in increased annual maintenance expenses for sewer management. FSEs are required to recover FOG at the point of generation by installing grease interceptors (GIs) before releasing wastewater into the sewer system, thereby restricting the amount of FOG that is deposited. The successful control of FOG deposition is largely dependent on gaining a thorough understanding of its intricate features, pretreatment methods, and deposition mechanisms, as well as increasing public awareness of the issue. For the purpose of providing an overview of the components and characteristics of FOGs, this review is presented. Additionally, it critically discusses the potential sources of FOGs, the effects of FOGs on sewage systems, and the problems that are associated with wastewater treatment plants. In addition, it evaluates the mechanisms that are responsible for the deposition of FOG as well as potential control techniques. Various key removal procedures, such as physical, chemical, and biological approaches, have been described in this review. In order to help in the process of developing a sustainable urban environment, it is necessary to evaluate the progress that has been made in terms of procedures and techniques in order to identify the future evolution of FOG waste management. Graphical abstract

The UV treatment of 6:2 FTAB involves the mitigation of this persistent chemical by the impact of ultraviolet radiation, which is known for its resistance to environmental breakdown. UV treatment of PFOA and/or 6:2 FTAB, and the role of responsible species and their mechanism have been presented. Our investigation focused on the degradation of perfluorooctanoic acid (PFOA) and 6:2 fluorotelomer sulfonamide alkyl betaine (6:2 FTAB, Capstone B), using UV photolysis under various pH conditions. Initially, we used PFOA as a reference, finding a 90% decomposition after 360 min at the original (unadjusted) pH 5.6, with a decomposition rate constant of (1.08 ± 0.30) × 10⁻⁴ sec⁻¹ and a half-life of 107 ± 2 min. At pH 4 and 7, degradation averaged 85% and 80%, respectively, while at pH 10, it reduced to 57%. For 6:2 FTAB at its natural pH 6.5, almost complete decomposition occurred. The primary UV transformation product was identified as 6:2 fluorotelomer sulfonic acid (6:2 FTSA), occasionally accompanied by shorter-chain perfluoroalkyl acids (PFAAs) including PFHpA, PFHxA, and PFPeA. Interestingly, the overall decomposition percentages were unaffected by pH for 6:2 FTAB, though pH influenced rate constants and half-lives. In PFOA degradation, direct photolysis and reaction with hydrated electrons were presumed mechanisms, excluding the involvement of hydroxyl radicals. The role of superoxide radicals remains uncertain. For 6:2 FTAB, both direct and indirect photolysis were observed, with potential involvement of hydroxyl, superoxide radicals, and/or other reactive oxygen species (ROS). Clarification is needed regarding the role of $e_{aq}^{-}$ in the degradation of 6:2 FTAB.

This study aims to estimate the organic load of oily wastewater by using Chemical Oxygen Demand (COD) measurements, addressing the analytical challenges posed by the hydrophobic, nonpolar, and often emulsified nature of Fats, oil and grease (FOG). This study established a reproducible and practical methodology for measuring COD in wastewater containing FOG at a laboratory scale, utilizing the nonionic surfactant T80 as a solubilizing and emulsifying agent. Precise gravimetric methods were employed to measure the mass of T80 (indirectly from volume (100–1400 µL/L)) added, and its correlation with COD was established. A strong linear relationship (R² = 0.993–0.998) between T80 concentration and COD confirmed its stability and suitability as a calibration standard. Experiments with sunflower (1–4 mL/L) and rapeseed oils (1–3 mL/L) showed that COD increased linearly with oil concentration and stabilized after prolonged mixing (96–120 h), indicating complete emulsification and micellar equilibrium. Even under T80 overdose conditions, COD retained linearity (R² > 0.99), though absolute values were elevated due to excess surfactant oxidation. Temperature variation (5 and 20 °C) and mild heating of coconut fat (30–32 °C) showed no significant effect on COD reproducibility, indicating that mixing time and surfactant dosage are the dominant factors influencing measurement accuracy. Overall, the study establishes T80 as a reliable surfactant for solubilizing oily matrices, providing a consistent and repeatable approach for COD assessment of wastewater containing FOG. The proposed method offers a practical basis and a step towards environmental monitoring and process control in decentralized and industrial wastewater treatment systems.