Antibiotics, disinfectants and bacteria resistant to them have been detected in environmental compartments such as waste water, surface water, ground water, sediments and soils. Antibiotics are released into the environment after their use in medicine, veterinary medicine and their employment as growth promoters in animal husbandry, fish farming and other fields. There is increasing concern about the growing resistance of pathogenic bacteria in the environment, and their ecotoxic effects. Increasingly, antibiotic resistance is seen as an ecological problem. This includes both the ecology of resistance genes and that of the resistant bacteria themselves. Little is known about the effects of subinhibitory concentrations of antibiotics and disinfectants on environmental bacteria, especially with respect to resistance. According to the present state of our knowledge, the impact on the frequency of resistance transfer by antibacterials present in the environment is questionable. The input of resistant bacteria into the environment seems to be an important source of resistance in the environment. The possible impact of resistant bacteria on the environment is not yet known. Further research into these issues is warranted.

Resistance in the Environment

This exhaustive review focuses on the fundamental principles and applications of heterogeneous electrochemical wastewater treatment based on Fenton’s chemistry reaction. The elementary equations involved in formation of hydroxyl radical in homogeneous electro-Fenton (EF) and photo electro-Fenton (PEF) processes was presented and the advantages of using insoluble solids as heterogeneous catalyst rather than soluble iron salts (heterogeneous electro-Fenton process) (Hetero-EF) was enumerated. Some of the required features of good heterogeneous catalysts were discussed, followed by the mechanisms of catalytic activation of H2O2 to reactive oxygen species (ROS) especially hydroxyl radical ( OH) by heterogeneous catalyst in Hetero-EF system. Extensive discussion on the two configuration of Hetero-EF system vis-a-vis added solid catalysts and functionalized cathodic materials were provided along with summaries of some relevant studies that are available in literature. The solid catalysts and the functionalized cathodic materials that have been utilized in Hetero-EF wastewater treatment were grouped into different classes and brief discussion on their synthesis route were given. Besides, the use of solid catalysts and iron-functionalized cathodic materials in bioelectrochemical system (BES) especially bioelectro-Fenton technology (BEF) using microbial fuel cells (MFCs) with concurrent electricity generation for Hetero-EF treatment of biorefractory organic pollutants was discussed. In the final part, emphasis was made on the challenges and future prospects of the Hetero-EF for wastewater treatment.

Heterogeneous electro-Fenton and photoelectro-Fenton processes: A critical review of fundamental principles and application for water/wastewater treatment

Heterogeneous Fenton catalysts: A review of recent advances.

Various cell architectures of capacitive deionization: Recent advances and future trends.

Current advances and trends in electro-Fenton process using heterogeneous catalysts - A review.

Development of a novel graphene/Co3O4 composite for hybrid capacitive deionization system

Environmental Applications of Boron‐Doped Diamond Electrodes: 1. Applications in Water and Wastewater Treatment

Conversion of sewage sludge into biochar: A potential resource in water and wastewater treatment.

Oxidation of recalcitrant organic contaminants via the electrogenerated sulfate radicals (SO4 −) with boron doped diamond (BDD) electrode is one of the most efficient techniques. In this review, fundamental mechanisms of sulfate (SO42−), persulfate (PS, S2O82−) and peroxymonosulfate (PMS, HSO5−) activation with BDD anode and its environmental applications are discussed. Significance of BDD electrode properties such as sp3/sp2 ratio, doping agents and substrate material, and the influence of electrolyte medium, current density and the presence of other inorganic ions (chloride, carbonate, nitrate, phosphate) on the electrogeneration of reactive sulfate species and its reactivity is comprehended as followingly, (i) BDD-sulfate process explains the fundamental reaction mechanisms involving in the electrogeneration of SO4 −and S2O82− via radical and non-radical routes, (ii) electrochemical activation of electrogenerated/externally added PS and PMS via the direct/indirect pathways and its promotional reactions are detailed, and (iii) mode of reactivity of the electrogenerated reactive sulfate species with organic contaminants in synthetic and real water, wastewater and soil matrices is elaborated. Most of the studies reported the activation of SO42− at current densities ≥10 mA cm−2, and the energy consumption in the range of 41–190 kW h m−3 was reported for the treatment (95–100% removal efficiency) of high organic content real wastewaters. In later section, the importance of coupling other processes such as electrogeneration of H2O2, UV irradiation, and membrane distillation with BDD/sulfate system to enhance the performance efficiency is discussed. Future perspectives of the research and application is presented at the end.

Govindaraj Divyapriya

Papers

Development of a novel graphene/Co3O4 composite for hybrid capacitive deionization system

Environmental Applications of Boron‐Doped Diamond Electrodes: 1. Applications in Water and Wastewater Treatment

Conversion of sewage sludge into biochar: A potential resource in water and wastewater treatment.

Electrochemically generated sulfate radicals by boron doped diamond and its environmental applications

Ferrocene functionalized graphene based electrode for the electro-Fenton oxidation of ciprofloxacin.