Dosing low-level ferrous iron in coagulation enhances the removal of micropollutants, chlorite and chlorate during advanced water treatment

An insight into the role of experimental parameters in advanced oxidation process applied for pharmaceutical degradation

The advanced oxidation process (AOP) is an efficient method to treat recalcitrance pollutants such as pharmaceutical compounds. The essential physicochemical factors in AOP experiments significantly influence the efficiency, speed, cost, and safety of byproducts of the treatment process. In this review, we collected recent articles that investigated the elimination of pharmaceutical compounds by various AOP systems in a water medium, and then we provide an overview of AOP systems, the formation mechanisms of active radicals or reactive oxygen species (ROS), and their detection methods. Then, we discussed the role of the main physicochemical parameters (pH, chemical interference, temperature, catalyst, pollutant concentration, and oxidant concentration) in a critical way. We gained insight into the most frequent scenarios for the proper and improper physicochemical parameters for the degradation of pharmaceutical compounds. Also, we mentioned the main factors that restrict the application of AOP systems in a commercial way. We demonstrated that a proper adjustment of AOP experimental parameters resulted in promoting the treatment performance, decreasing the treatment cost and the treatment operation time, increasing the safeness of the system products, and improving the reaction stoichiometric efficiency. The outcomes of this review will be beneficial for future AOP applicants to improve the pharmaceutical compound treatment by providing a deeper understanding of the role of the parameters. In addition, the proper application of physicochemical parameters in AOP systems acts to track the sustainable development goals (SDGs).

Advanced oxidation of recalcitrant chromophores in full-scale MBR effluent for non-potable reuse of leachate co-treated municipal wastewater

Wastewater non-potable reuse involves further processing of secondary effluent to a quality level acceptable for reuse and is a promising solution to combating water scarcity. Recalcitrant chromophores in landfill leachate challenge the water quality for non-potable reuse when leachate is co-treated with municipal wastewater. In this study, we first use multivariate statistical analysis to reveal that leachate is an important source (with a Pearson's coefficient of 0.82) of recalcitrant chromophores in the full-scale membrane bioreactor (MBR) effluent. We then evaluate the removal efficacies of chromophores by chlorination, breakpoint chlorination, and the chlorination-UV/chlorine advanced oxidation treatment. Conventional chlorination and breakpoint chlorination only partially remove chromophores, leaving a colour level exceeding the standards for non-potable reuse (>20 Hazen units). We demonstrate that pre-chlorination (with an initial chlorine dosing of 20 mg/L as Cl2) followed by UV radiation (with a UV fluence of 500 mJ/cm2) effectively degraded recalcitrant chromophores (>90%). By quantifying the electron donating capacity (EDC) and radical scavenging capacity (RSC) of the reclaimed water, we demonstrate that pre-chlorination reduces EDC and RSC by up to 64%, increases UV transmittance by 32%, and increases radical yields from UV photolysis of chlorine by 1.7-2.2 times. The findings advance fundamental understanding of the alteration of dissolved coloured substances by (photo)chlorination treatment and provide implications for applying advanced oxidation processes in treating wastewater effluents towards sustainable non-potable reuse.

Microwave-Reactor-Based Preparation of Red Iron Oxide Pigment from Waste Iron Sulfate

This article presents a two-step method of iron red synthesis based on waste long-term deposited iron(II) sulfate. The first step is the purification of waste iron sulfate, and then the pigment is synthesized by precipitation using a microwave reactor. The newly developed method of purification allows for quick and thorough purification of iron salt. The use of a microwave reactor in the synthesis of iron red makes it possible to reduce the temperature of the goethite-hematite phase transition from 500 °C to 170 °C and skip the calcination process. A temperature reduction in the synthesis decreases the formation of agglomerates of synthesized materials compared to commercial ones. The results of the research showed a change in the physicochemical properties of the obtained pigments depending on the conditions of synthesis. Waste iron(II) sulfate is a promising raw material for the synthesis of iron red pigments. Laboratory pigments are found to be differ from commercial pigments. The difference in properties speaks in favor of synthesized materials.

Photolysis of chlorite by solar light: An overlooked mitigation pathway for chlorite and micropollutants

Chlorite (ClO₂^-) is an undesirable toxic byproduct commonly produced in the chlorine dioxide and ultraviolet/chlorine dioxide oxidation processes. Various methods have been developed to remove ClO₂^- but require additional chemicals or energy input. In this study, an overlooked mitigation pathway of ClO₂^- by solar light photolysis with a bonus for simultaneous removal of micropollutant co-present was reported. ClO₂^- could be efficiently decomposed to chloride (Cl^-) and chlorate by simulated solar light (SSL) at water-relevant pHs with Cl^- yield up to 65% at neutral pH. Multiple reactive species including hydroxyl radical (•OH), ozone (O₃), chloride radical (Cl•), and chlorine oxide radical (ClO•) were generated in the SSL/ClO₂^- system with the steady-state concentrations following the order of O₃ (≈ 0.8 μΜ) > ClO• (≈ 4.4 × 10^-6 μΜ)> •OH (≈ 1.1 × 10^-7 μΜ)> Cl• (≈ 6.8 × 10^-8 μΜ) at neutral pH under investigated condition. Bezafibrate (BZF) as well as the selected six other micropollutants was efficiently degraded by the SSL/ClO₂^- system with pseudofirst-order rate constants ranging from 0.057 to 0.21 min^-1 at pH 7.0, while most of them were negligibly degraded by SSL or ClO₂^- treatment alone. Kinetic modeling of BZF degradation by SSL/ClO₂^- at pHs 6.0 - 8.0 suggested that •OH contributed the most, followed by Cl•, O₃, and ClO•. The presence of water background components (i.e., humic acid, bicarbonate, and chloride) exhibited negative effects on BZF degradation by the SSL/ClO₂^- system, mainly due to their competitive scavenging of reactive species therein. The mitigation of ClO₂^- and BZF under photolysis by natural solar light or in realistic waters was also confirmed. This study discovered an overlooked natural mitigation pathway for ClO₂^- and micropollutants, which has significant implications for understanding their fate in natural environments.

Chlorine dioxide-based oxidation processes for water purification：A review

Chlorine dioxide (ClO₂) has emerged as a broad-spectrum, safe, and effective disinfectant due to its high oxidation efficiency and reduced formation of organochlorinated by-products during application. This article provides an updated overview of ClO₂-based oxidation processes used in water treatment. A systematic review of scientific information and experimental data on ClO₂-based water purification procedures is presented. Concerning ClO₂-based oxidation derivative problems, the pros and cons of ClO₂-based combined processes are assessed and disinfection by-product (DBP) control approaches are proposed. The kinetic and mechanistic data on ClO₂ reactivity towards micropollutants are discussed. ClO₂ selectively reacts with electron-rich moieties (anilines, phenols, olefins, and amines) and eliminates certain inorganic ions and microorganisms with high efficiency. The formation of chlorite and chlorate during the oxidation process is a crucial concern when utilizing ClO₂. Future applications include the combination of ClO₂ with ferrous ions, activated carbon, ozone, UV, visible light, or persulfate processes. The combined process can reduce by-product generation while still ensuring ClO₂ sterilization and disinfection. Overall, this research could provide useful information and new insights into the application of ClO₂-based technologies.