Remediation of water pollution caused by pharmaceutical residues based on electrochemical separation and degradation technologies: A review

The presence of pharmaceutical micropollutants in the environment has become of major concern in the last decades. Many electrochemical technologies are currently available for the remediation of waters contaminated by refractory organic pollutants. They are mainly defined as eco-friendly water treatments since the main reagent involved is a clean species, the electron. Recent reviews have focused on the destruction of pharmaceutical residues by the application of methods like ozonation and advanced oxidation processes. Here, we present an overview on electrochemical methods devised for the removal of pharmaceutical residues from both synthetic solutions and real pharmaceutical wastewaters. The fundamentals and experimental set-ups involved in different technologies such as electrocoagulation, anodic oxidation, electro-oxidation with active chlorine, electro-Fenton, photoelectro-Fenton, and photoelectrocatalysis, among others, are discussed. Progress on the promising solar photoelectro-Fenton process devised and further developed in our laboratory is especially highlighted and documented. The destruction of the individual pharmaceuticals and the abatement of total organic carbon or reduction of chemical oxygen demand allow the comparison between the different methods. In some cases, the routes for the complete degradation of the initial pollutants are discussed.

Catalytic wet air oxidation of substituted phenols using activated carbon as catalyst

Enhancing wastewater treatment efficiency through hydrodynamic cavitation and advanced oxidation processes: Experimental insights and comparative analysis

In this study a comparative assessment using various advanced oxidation processes (UV/H2O2, UV/H2O2/Fe(II), O3, O3/UV, O3/UV/H2O2 and O3/UV/H2O2/Fe(II)) was attempted to degrade efficiently two fluoroquinolone drugs ENR [enrofloxacin (1-Cyclopropyl-7-(4-ethyl-1-piperazinyl)-6-fluoro-1,4-dihydro-4-oxo-3-quinolonecarboxylic acid)] and CIP [ciprofloxacin (1-cyclopropyl-6-fluoro-4-oxo-7-(piperazin-1-yl)-quinoline-3-carboxylic acid)] in aqueous solutions at a concentrations of 0.15 mM for each drug. The efficiency of the applied oxidation processes (AOPs) has been estimated by the conversion of the original substrate (XENR and XCIP) and the reduction of chemical oxygen demand (COD), total organic carbon (TOC). Special emphasis was laid on the effect of varying reaction pH as well as of the applied oxidant doses on the observed reaction kinetics for each advanced oxidation processes. High degradation efficiencies, particularly in terms of rates of TOC and COD abatement, were obtained for photo-Fenton assisted ozonation [O3/UV/H2O2/Fe(II)], compared to other advanced oxidation processes. At pH 3 and 25°C best results for the degradation of both investigated drugs were achieved when 10 mM H2O2, 0.5 mM Fe(II) and an initial dose of 8.5 mg L−1 ozone were applied. In addition, the evolution of toxicity of the reaction mixtures for different AOPs has been studied by the bioluminescence test (LUMIStox 300).

Electrochemical-based approaches for the treatment of pharmaceuticals and personal care products in wastewater

Most of electrochemical advanced oxidation processes (EAOP´s) such as the electroFenton (EF), photo electroFenton (PEF), solar photo electroFenton (SPEF) and electro-peroxone (E-peroxone) processes use hydrogen peroxide (H2O2) as its core reactant due to its possibility to react with some catalysts (Fe2+, O3) yielding high oxidant hydroxyl radicals to be used in the degradation of persistent organic pollutants [1]. Carbonaceous materials like carbon felt, carbon cloth and reticulated vitreous carbon (RVC) are the most used because of its capability to accumulate H2O2 [2,3]. The use of these materials is often in gas diffusion electrodes which are based in the injection of air from an external source to an air chamber located behind the electrode allowing the dispersion of the gas inside the electrode promoting the oxygen reduction [3]. This work deals with the in situ electrosynthesis of H2O2 in a flow through reactor using RVC as cathode material and Ti|Ir-Ta oxides expanded mesh as anode to improve the oxygen evolution reaction with subsequent reduction of O2 on the RVC to yield H2O2. The electrochemical cell consists of a flow channel where the electrodes are placed along its length, allowing the electrolyte to flow through them forcing the transport of oxygen bubbles inside the porous carbon material for its reduction to H2O2. [1] Sirés I., Brillas., E. Remediation of water pollution caused by pharmaceutical residues sed on electrochemical separation and degradation technologies: A review. Environmental International, 40 (2018) 212-229. [2] Coria G., Pérez T., Sirés I., Nava J.L., Mass transport studies during dissolved oxygen reduction to hydrogen peroxide in a filter-press electrolyzer using graphite felt, reticulated vitreous carbon and boron-doped diamond as cathodes. Journal of Electroanalytical Chemistry, 757 (2015) 225-229. [3] Pérez T., Coria G., Sirés I., Nava J.L., Uribe A.R., Electrosynthesis of hydrogen peroxide in a filter-press flow cell using graphite felt as air-diffusion cathode. Journal of Electroanalytical Chemistry, 812 (2018) 54-58.

Over the last years pharmaceuticals have been receiving a lot of attention as emergent pollutants worldwide. These compounds can reach the environment through many vias, i.e. excretion in urine and faeces of humans and livestock, household disposal or hospital wastes and their concentration in water can vary between ng L-1 to mg L-1 [1]. Despite their low concentration these persistent organics can have adverse effects on the environment, for this reason its elimination is a big concern. Different processes have been tried to remove these compounds from water among which are the electrochemical advanced oxidation processes (EAOP´s) like electroFenton (EF), photo electroFenton (PEF), solar photo electroFenton (SPEF) and electro-peroxone (E-peroxone) [1]. E-peroxone is a relatively new process that employs two reactants, the electrogenerated hydrogen peroxide (via O2 reduction in acidic media) and ozone to produce homogeneous hydroxyl radicals [2]. The E-peroxone process has been studied for the removal of several pharmaceuticals showing great potential in their elimination from water [3]. This work deals with the removal of the antibiotic Levofloxacin (LVN) from synthetic wastewater using the E-peroxone process. The electrolyzes were performed in a laboratory flow plant containing 1.5 dm3 of solution having 50 mg dm-3 of LVN and 0.05 M NaSO4 as background electrolyte at pH 3; a Ti-Ir-Sn-Sb oxides was used as anode and a graphite felt on top of carbon cloth was used as gas diffusion cathode [4], where compressed air was fed at 0.36 psi of pressure. The trials were conducted at a constant cathodic potential (Ecat ) of -0.3 V vs SHE at a volumetric rate (Q) of 1.5 dm3 min-1. The results showed a chemical oxygen demand (COD) decay of 70 % at 6 hours of electrolysis. The influence of current density, O3 feed and initial concentration of LVN on the rate of degradation of LVN and mineralization current efficiency was also analyzed. Finally, the by-products of LVN were followed by chromatographic techniques to propose a reaction pathway. [1] Sirés I., Brillas., E. Remediation of water pollution caused by pharmaceutical residues sed on electrochemical separation and degradation technologies: A review. Environmental International, 40 (2018) 212-229. [2] Li X., Wang Y., Yuan S., Li Z., Wang B., Huang J., Deng S., Yu G. Degradation of the anti-inflammatory drug ibuprofen by electro-peroxone process. Water Research, 63 (2014) 81-93. [3] Wang H., Zhan J., Yao W., Wang B., Deng S., Huang J., Yu G., Wang Y. Comparison of pharmaceutical abatement in various water matrices by conventional ozonation, peroxone (O3/H2O2), and an electro-peroxone process. Water Research, 130 (2018) 127-138. [4] Pérez T., Coria G., Sirés I., Nava J.L., Uribe A.R. Electrosynthesis of hydrogen peroxide in a filter-press flow cell using graphite felt as air diffusion cathode. Journal of Electroanalytical Chemistry, 812 (2018) 54-58.

Industrial wastewater containing dyes, antibiotics, heavy metal ions and other refractory organic pollutants has complicated components and poor biodegradability. Comparing to traditional bio-treatment processes, electrochemical technologies have significant advantage in treating such kinds of wastewater due to the electrochemically generated reactive species. Modifying the electrodes with catalytic components can enhance pollutant removal capacity in electro-catalytic (EC) or photo-electro-catalytic (PEC) integrated systems, but high energy consumption of electricity still restricts their implement. Self-biased fuel cells, including photocatalytic fuel cells (PFCs) and microbial fuel cells (MFCs), are more sustainable in industrial wastewater/pollutants treatment. Highly active catalytic electrodes are essential to promote pollutant removal and energy conservation. This article reviews the recent development of novel catalytic electrodes in preparation, optimization and sustainable application for industrial wastewater treatment. Technical advantages and optimization spaces of fuel-cell integrated systems (based on PFCs and MFCs) are introduced, and their challenges in large-scale application are pointed out. Catalytic electrodes have broader application fields than powder-form catalysts due to the easy-recyclability and the synergy of catalysis and electrochemistry. An ideal catalytic electrode should be conductive, highly (photo-)electro-active, physically and chemically stable, easy to prepare and low-cost. By optimizing the preparation/loading of novel catalytic materials (heterojunctions, single-atom catalysts etc.), various catalytic electrodes, in forms of self-standing (metal-based, carbon-based and others), film/membrane and particles, etc., can be obtained with extraordinary (photo-)electro-catalytic activity. Innovative design of catalytic electrodes in structure and component may in-situ integrate multiple technologies such as (photo-)electro-catalysis, advanced oxidation processes (AOPs) and membrane filtration, etc., which provides more possibility for enhancing electrochemical systems. Novel catalytic electrode of low-cost and high efficiency is still desirable for further optimization of integrated electrochemical systems. PFCs convert solar energy into electricity from the wastes (fuels). Various PFCs (single or dual photo-electrode(s)) have been developed for the degradation of dyes, antibiotics and other refractory pollutants. The electricity generation of novel PFC has been improved to 1 V (open circuit voltage) or more in some cases. Enhanced pollutant degradation and energy recovery by optimizing the function of electrode and structure of PFCs are still desirable for complex wastewater treatment. By using exoelectrogens, highly-active catalytic electrodes (anode and/or cathode) can be applied in MFC integrated systems to promote the degradation of refractory pollutants. The synergy of bacteria and catalytic electrodes broadens the application of bio-processes in industrial wastewater treatment, and also benefits the energy recovery (electricity, hydrogen, heavy metals, etc.) of systems. Innovative designs of systems are expected to further reduce the operating costs from ion-exchange membrane, light irradiation and aeration. Although pollutant removal and energy conservation of fuel cells can be further improved by integrating AOPs (Fenton process, sulfate or chlorine radical advanced oxidation, etc.) or combining other processes (EC, PEC, desalination, etc.), less chemical consumption and simpler system configuration/operation are the main trends of sustainable and cleaner production. In the future, efforts need to be done for large-scale industrial wastewater treatment by fuel cell systems: (1) Develop novel catalytic electrodes of low-cost with enhanced performance (visible light response) and integrated functions (photo- and/or electro-catalysis, filtration, AOPs, etc.). (2) Construct novel integrated fuel cell systems with highly active catalytic electrodes for multiple pollutant control and energy recovery. (3) Optimize large-scale preparation of catalytic electrodes, and simplify the operations of fuel cell systems, for energy-efficient and cost-effective treatment of real industrial wastewater, during long-term run.

Differential pulse voltammetry as a powerful tool to monitor the electro-Fenton process

Background:One of the basic practices in the field of waste management is the collection and treatment of leachate. Leachate from municipal waste due to high chemical oxygen demand (COD) and dark color is a potential pollutant of the environment, which causes a lot of problems in the absence of treatment and direct discharge to the environment. This study aimed to determine the efficiency of ultrasonic process in combination with coagulation and flocculation process using sodium ferrate in COD and color reduction.Materials and Methods:In this experimental study, all experiments were performed in batch conditions and with changing process variables such as pH and sonication time, and the effect of three parameters, including ultrasonic reaction time (15, 30, and 45 min), pH (2, 4, 5/5, and 7), and coagulant dosage (from 1 to 150 g/l) on the COD reduction and color removal, was evaluated. Coagulant concentration and then the removal efficiency of COD and color were analyzed by ANOVA using SPSS 18.Results:The COD reduction and color removal were 87.05% and 88.6% in optimal condition (using 120 g/L of sodium ferrate at pH 5.5), with coagulation/flocculation, after ultrasound (15 min). Ultrasound (15 min) + sodium ferrate (without coagulation/flocculation) achieved 46.25% of COD reduction and 90.35% of color elimination, whereas the ultrasonic process alone allowed removing the COD and color in the leachate by less than 50%.Conclusion:The results indicate that C–F followed by ultrasonic can be used to efficiently reduce the organic matter and color from municipal waste leachate, and it would be an ideal option for leachate treatment.

Herbicides have been largely utilized during the last decades to maintain the quality and quantity of agricultural crop, ensuring the need of an increasing world food production. However, these synthetic organics are highly biorecalcitrant and stable at mild conditions and cannot be effectively destroyed in conventional wastewater treatment facilities. Among the advanced oxidation processes used to remove herbicides, electrochemical technologies have been recently developed at bench scale as potential powerful treatments. This review presents a critical, exhaustive and detailed analysis on the application of single and combined electrochemical advanced oxidation processes to remediate wastewaters and soils contaminated with common herbicides, covering the period 2010–2019. Nine kinds of treatments, including single methods like anodic oxidation, anodic oxidation with electrogenerated H 2 O 2 , homogeneous and heterogeneous electro-Fenton, photoelectro-Fenton, solar photoelectro-Fenton and photoelectrocatalysis, as well as combined ones involving hybrid and sequential processes, have been examined. The fundamentals of each technology are briefly described, and the main results obtained for the removal of the most used herbicide families from synthetic solutions and soil-washing effluents are carefully exposed and discussed. The role of generated oxidizing agents and/or photolytic reactions in photo-assisted processes is explained to justify the mechanisms proposed for herbicide mineralization. The comparative oxidation ability of the different methods is discussed. Finally, future challenges remarking the need of treating real agricultural wastewaters and contaminated soils, the construction of electrochemical systems with stable electrodes at industrial scale and the realization of techno-economic studies are envisaged. • Review of 9 treatments with EAOPs for herbicide removal from wastewaters and soils (2010–2019). • Application of single and combined processes to synthetic herbicide solutions. • Rapid degradation of herbicides and overall mineralization feasible with BDD anodes. • Superiority of SPEF for wastewater treatment due to the positive action of sunlight irradiation. • Better performance for soil-washing effluents remediation by photoelectrolysis with UVC light.

Pretreatment of wastewater from triazine manufacturing by coagulation, electrolysis, and internal microelectrolysis

A comprehensive review of the Fenton-based approaches focusing on landfill leachate treatment

Application of pyrite to water pollutant removal: A review

Comparative overview of advanced oxidation processes and biological approaches for the removal pharmaceuticals