Solar-assisted electrooxidation process for enhanced degradation of bisphenol A: Performance and mechanism

PMS coupled Mn(II) mediated electrochemistry processes (E-Mn(II)-PMS) on the efficient RB19 wastewater treatment: Focus on the regulation and reinforcement of Mn(III)/Mn(II)

Dye wastewater, represented by reactive blue 19 (RB19), severely threatens the aquatic ecological environment and human health, such that an efficient RB19 wastewater treatment technology should be urgently developed. Based on manganese ion-mediated electrochemistry, PMS was introduced to develop a novel electrocatalytic system (E-Mn(II)-PMS) that can efficiently remove and degrade RB19. The synergistic effect between E, Mn(II), and PMS was verified in this study through comparative experiments of a wide variety of systems. The removal efficiency of RB19 reached 95.1% in 50 min under reasonable power consumption (3.29 kWh/m3). Moreover, the effects exerted by different operating conditions (e.g., initial pH, current density, RB19 concentration, Mn(II) concentration, as well as PMS concentration) and water matrix on the degradation efficiency of RB19 were explored through single factor experiments. The active oxidation species (ROS) and their contribution rate for the degrading and removing RB19 were studied through quenching experiments, EPR experiments, TMT-15 metal capture experiments, as well as PP complexation experiments. The role played by non-free radicals took on critical significance in the oxidation removal of RB19, which comprised direct electro oxidation, Mn(III) oxidation, and 1O2 oxidation. The enhancement effect of free radicals (SO4·- and HO∙) was not sufficiently significant, with a low degree of contribution. The oxidation effect of the anode facilitated the conversion of Mn (II) to Mn (III), which was employed in PMS for expediting the production of 1O2. The reduction effect of the cathode blocked the production of Mn (IV) as a side reaction, such that the continuous circulation of manganese ions between divalent and trivalent was promoted. Meanwhile, the cathode reacted with PMS to generate a small part of SO4·- and HO∙. In addition, the reaction active site of RB19 was predicted, and a possible degradation pathway was proposed in accordance with the mass spectrometry results and the DFT calculation. As revealed by the results of the QSAR analysis and the plant culture experiments, the biological toxicity of RB19 was markedly reduced after the sample was administrated with E-Mn(II)-PMS. E-Mn(II)-PMS-mediated electrochemical technology displays several advantages (e.g., high efficiency, low consumption, recyclability, wide pH window, and strong applicability) while showing promising market development and utilization for treating dye wastewater.

Bisphenols in water: Occurrence, effects, and mitigation strategies

Bisphenols (bisphenol A (BPA), bisphenol S (BPS), bisphenol F (BPF) and bisphenol AF (BPAF)) are widely used as additives in numerous industries and therefore they are ubiquitously present throughout the world's natural environment including water. A review of the literature is presented on their sources, pathways of entry into the environment, and especially aquatic contexts, their toxicity to humans and other organisms and the technologies for removing them from water. The treatment technologies used are mostly adsorption, biodegradation, advanced oxidation, coagulation, and membrane separation processes. In the adsorption process, several adsorbents, especially carbon-based materials, have been tested. The biodegradation process has been deployed and it involves a variety of micro-organisms. Advanced oxidation processes (AOPs) such as UV/O₃-based, catalysis relevant AOPs, electrochemical AOPs and physical AOPs have been employed. Both the biodegradation process and AOPs generate by-products which may be toxic. These by-products need to be subsequently removed using other treatment processes. Effectiveness of the membrane process varies depending on the porosity, charge, hydrophobicity, and other properties of the membrane. The problems and limitations of each treatment technique are discussed and methods to overcome them are presented. Suggestions are articulated to use a combination of processes to improve the removal efficiencies.

A critical review of textile industry wastewater: green technologies for the removal of indigo dyes

The denim textile industry represents an important productive sector. It generates wastewater with low biodegradability due to the presence of persistent pollutants, which can produce toxic and carcinogenic compounds; therefore, wastewater treatment reduces risks to aquatic life and public health. This paper presents a review of 172 papers regarding textile industry wastewater treatment for the removal of contaminants, especially indigo dyes used in the denim industry, in the context of green technologies. The physicochemical characteristics of textile wastewater, its environmental and health impacts, and the permissible limit regulations in different countries were reviewed. Biological, physicochemical and advanced oxidation processes for the removal of indigo dyes were reviewed. The goal of this study was to analyze the characteristics of green technologies; however, the research does not clearly demonstrate an effect on energy consumption savings, carbon footprint decreases, and/or waste generation. Advanced oxidation processes showed the highest color removal efficiency (95 and 97% in synthetic or real wastewater, respectively). Photocatalysis and Fenton reactions were the most efficient processes. None of the revised works presented results regarding upscaling for industrial application, and the results should be discussed in terms of the guidelines and maximum permissible limits established by international legislation. New technologies need to be developed and evaluated in a sustainable context with real wastewater.