Homogenous UV/periodate process in treatment of p-nitrophenol aqueous solutions under mild operating conditions

Thermo-activated periodate oxidation process for tetracycline degradation: Kinetics and byproducts transformation pathways

Periodate-based advanced oxidation processes have been diffusely practiced for pollutant decontamination. However, the thermo-activation of periodate process (heat/PI), an effective water pollution removal process, has been rarely discussed, and the degradation pathway of this heat/PI system requires investigation. In this work, tetracycline antibiotics were selected as the model micropollutant for the comprehensive evaluation of the heat/PI system. The heat/PI system exhibited good performance for tetracycline (TC) remediation with temperature increases. The principal reactive oxidative species in the heat/PI system was confirmed using quenching experiments and electron paramagnetic resonance experiments. Further, the potential reactive sites in the TC were identified based on the density functional theory calculation. Based on the detection results of intermediates, there was no significant difference in byproducts generated during TC degradation under various temperatures in the heat/PI system. The Toxicity Estimation Software Tool (T.E.S.T.) method was applied to calculate the individual toxicity of the byproducts. This study contributes to a comprehensive explanation of the process of the thermal activation of periodate, and in particular, it explains the source of oxidation power, the transformation of byproducts, and the toxicity of reaction systems.

Emerging periodate-based oxidation technologies for water decontamination: A state-of-the-art mechanistic review and future perspectives

With the ever-increasing severity of the ongoing water crisis, it is of great significance to develop efficient, eco-friendly water treatment technologies. As an emerging oxidant in the advanced oxidation processes (AOPs), periodate (PI) has received worldwide attention owing to the advantages of superior stability, susceptible activation capability, and high efficiency for decontamination. This is the first review that conducts a comprehensive analysis of the mechanism, pollutant transformation pathway, toxicity evolution, barriers, and future directions of PI-based AOPs based on the scientific information and experimental data reported in recent years. The pollutant elimination in PI-based AOPs was mainly attributed to the in situ generate reactive oxygen species (e.g., ^•OH, O(³P), ¹O₂, and O₂^•-), reactive iodine species (e.g., IO₃^• and IO₄^•), and high-valent metal-oxo species with exceptionally high reactivity. These reactive species were derived from the PI activated by the external energy, metal activators, alkaline, freezing, hydroxylamine, H₂O_2, etc. It is noteworthy that direct electron transport could also dominate the decontamination in carbon-based catalyst/PI systems. Furthermore, PI was transformed to iodate (IO₃^-) stoichiometrically via an oxygen-atom transfer process in most PI-based AOPs systems. However, the production of I₂, I^-, and HOI was sometimes inevitable. Furthermore, the transformation pathway of typical micropollutants was clarified, and the in silico QSAR-based prediction results indicated that most transformation products retained biodegradation recalcitrance and multi-endpoint toxicity. The barriers faced by the PI-based AOPs were also clarified with potential solutions. Finally, future perspectives and research directions are highlighted based on the current state of PI-based AOPs. This review enhances our in-depth understanding of PI-based AOPs for pollutant elimination and identifies future research needs to focus on the reduction of toxic byproducts.

Application of birnessite-type solids prepared by sol-gel and oxidation methods in photocatalytic degradation of 4-nitrophenol

Potassium birnessites were prepared using two methods, sol-gel or oxidation. The solids were characterised by element chemical analysis, powder X-ray diffraction, FT-IR spectroscopy, thermal analyses, and nitrogen adsorption. The evolution of the properties as a function of the preparation method was discussed. The photocatalytic performance of these solids was preliminarily tested for the degradation of 4-nitrophenol. The degradation pathway and the nature of the by-products were investigated by mass spectrometry. The solids showed good catalytic behaviour, although their preparation must be improved, mainly concerning the calcination step involved in sol-gel synthesis, which led to the formation of Mn₂O₃ that worsened the catalytic behaviour.

Improving waste activated sludge dewaterability with sodium periodate pre-oxidation on extracellular polymeric substances

The efficiency of sludge dewatering is affected by the structure and composition of hydrated extracellular polymeric substances (EPS). Degrading EPS can improve the sludge dewatering performance. As an oxidizing agent, sodium periodate (NaIO₄ ) has ability to oxidize organics, which is expected to decompose the protein and polysaccharide in EPS and improve the efficiency of sludge dewaterability. This study adopted NaIO₄ , for the first time, as an advanced oxidation agent to regulate EPS of waste activated sludge and was combined with anionic polyacrylamide (APAM) as a flocculant to subsequently enhance sludge dewatering. Response surface methodology (RSM) was used to determine the optimal conditions of pH, NaIO₄ , and APAM. The results showed that the composite conditioner's specific resistance of filtration (SRF) and the water content of the vacuum-filtered cake (Wc) were highly enhanced compared with those of the raw sludge (RS) under pH 6.5, a NaIO₄ concentration of 50 mg/g dry solids (DS), and an APAM concentration of 5 mg/g DS. Owing to the pre-oxidation achieved by NaIO₄ under a mildly acid environment, sludge flocs were broken. Subsequently, chemical coagulation (APAM) agglomerated the smaller particles into larger flocs of sludge by adsorption and bridging, thus improving sludge dewaterability. PRACTITIONER POINTS: A novel conditioner, pH/NaIO₄ /APAM, was explored for sludge dewatering. IO³ • and HO• oxidized extracellular polymeric substances (EPS). Degradation of the protein content of EPS released bound water. Highly enhanced sludge dewaterability was achieved under optimal conditions.

Efficiency and mechanism of 2,4-dichlorophenol degradation by the UV/IO4- process

This study explores the efficiency and kinetics of the photoactivated periodate process for the degradation of 2,4-dichlorophenol (2,4-DCP) in water. The obtained results show that the degradation rate was considerably higher for UV/IO₄^- compared to UV irradiation alone. Pseudo first-order reaction rate kinetics were obtained for all process conditions. The pH did not have a significant impact on the decomposition of 2,4-DCP using photoactivated periodate. Therefore, the applied method can be used to treat (waste)water at various pH. By raising the initial concentration of periodate to 5 mM, the degradation rate increased, while it decreased again at a concentration of 8 mM. As the 2,4-DCP concentration increased, the removal rate decreased. The extent of degradation was observed to be proportional with the UV intensity. A mechanistic study revealed that iodine radicals dominated the degradation of 2,4-DCP by photoactivated periodate, whereas OH and O(³P) only played a minor role. At pH 5.0, all chlorine atoms in 2,4-DCP were released as chloride ions in the UV/IO₄^- process, hence reaching a total dechlorination. Finally, the presence of inorganic salts, even at high levels, did not significantly impact the degradation. According to the results achieved in this study, the UV/IO₄^- system can be considered as a valuable alternative to treat effluents containing chlorinated organic compounds such as pulp and paper mill effluents and brine (waste)water.

Production of Reactive Oxygen Species by the Reaction of Periodate and Hydroxylamine for Rapid Removal of Organic Pollutants and Waterborne Bacteria

Periodate (PI, IO₄^-) can be activated by hydroxylamine (HA), resulting in the rapid removal of organic pollutants within seconds. While the previous studies on PI-based advanced oxidation processes (AOPs) have proposed iodate radical (^•IO₃) as the major reactive species, no evidence of ^•IO₃ production was found in the present PI/HA system. Reactive oxygen species (ROS) including ^•OH, HO₂^•, and ¹O₂ are proposed to be the main oxidants of the PI/HA system, which is supported by various tests employing the scavengers, chemical probes, and spin-trapping electron paramagnetic resonance (EPR) technique. To minimize the risk of toxic iodinated byproduct formation caused by reactive iodine species such as HOI and I₂, the molar ratio of HA/PI was optimized at 0.6 to achieve the stoichiometric conversion of IO₄^- to iodate (IO₃^-), a preferred nontoxic sink of iodine species. The PI/HA system also efficiently inactivated both Gram-positive and -negative bacteria with producing ¹O₂ as the dominant disinfectant. The mechanism of ROS production was also investigated and is discussed in detail. This work offers a simple and highly efficient option for PI activation and ROS production which might find useful applications where urgent and rapid removal of toxic pollutants is needed.

Catalytic degradation of p-nitrophenol by magnetically recoverable Fe3O4 as a persulfate activator under microwave irradiation

In this study, Fe₃O₄ and microwave (MW) were combined to activate persulfate (PS) for the removal of organic matter, resulting in the enhanced degradation of p-nitrophenol (PNP) in solution. During the preparation of Fe₃O₄, the effect of sodium acetate was examined, and the results showed that the concentration of sodium acetate had little effect on the catalytic activity of the Fe₃O₄/PS/MW system but did have an effect on the Fe₃O₄ yield. In addition, with regards to the representative environmental factors, the degradation experiment showed that humic acid and the co-existing anions of chloride, sulfate, nitrate, and phosphate had little effects on p-nitrophenol removal; however, carbonate had a negative effect. In addition, the Fe₃O₄/PS/MW system performed well in the initial pH range of 3.0-9.0. According to the quenching experiment and electron paramagnetic resonance (EPR) detection, sulfate radicals and a minority of hydroxyl radicals play dominant roles in the degradation process. In addition, the role of Fe₃O₄ was confirmed to take part in the degradation process by X-ray photoelectron spectroscopy (XPS) analysis. Because of the good performance observed in the water matrices of tap water and the Songhua River, these results demonstrate the potential application of the Fe₃O₄/PS/MW system for wastewater treatment.