Sulfate radical-based advanced oxidation processes (SR-AOPs) employing heterogeneous catalysts to generate sulfate radical (SO4 −) from peroxymonosulfate (PMS) and persulfate (PS) have been extensively employed for organic contaminant removal in water. This article aims to provide a state–of–the–art review on the recent development in heterogeneous catalysts including single metal, mixed metal, and nonmetal carbon catalysts for organic contaminants removal, with particular focus on PMS activation. The hybrid heterogeneous catalyst/PMS systems integrated with other advanced oxidation technologies is also discussed. Several strategies for the identification of principal reactive radicals in SO4 −–oxidation systems are evaluated, namely (i) use of chemical probe or spin trapping agent coupled with analytical tools, and (ii) competitive kinetic approach using selective radical scavengers. The main challenges and mitigation strategies pertinent to the SR-AOPs are identified, which include (i) possible formation of oxyanions and disinfection byproducts, and (ii) dealing with sulfate produced and residual PMS. Potential future applications and research direction of SR-AOPs are proposed. These include (i) novel reactor design for heterogeneous catalytic system based on batch or continuous flow (e.g. completely mixed or plug flow) reactor configuration with catalyst recovery, and (ii) catalytic ceramic membrane incorporating SR-AOPs.

Generation of sulfate radical through heterogeneous catalysis for organic contaminants removal: Current development, challenges and prospects

Application of peroxymonosulfate and its activation methods for degradation of environmental organic pollutants: Review

Advanced oxidation processes (AOPs) constitute important, promising, efficient, and environmental-friendly methods developed to principally remove persistent organic pollutants (POPs) from waters and wastewaters. Generally, AOPs are based on the in situ generation of a powerful oxidizing agent, such as hydroxyl radicals (•OH), obtained at a sufficient concentration to effectively decontaminate waters. This critical review presents a precise and overall description of the recent literature (period 1990–2012) concerning the main types of AOPs, based on chemical, photochemical, sonochemical, and electrochemical reactions. The principles, performances, advantages, drawbacks, and applications of these AOPs to the degradation and destruction of POPs in aquatic media and to the treatment of waters and waste waters have been reported and compared.

Advanced Oxidation Processes in Water/Wastewater Treatment: Principles and Applications. A Review

Over the last decades, research efforts have been made at developing more effective technologies for the remediation of waters containing persistent organic pollutants. Among the various technologies, the so-called electrochemical advanced oxidation processes (EAOPs) have caused increasing interest. These technologies are based on the electrochemical generation of strong oxidants such as hydroxyl radicals ( OH). Here, we present an exhaustive review on the treatment of various synthetic and real wastewaters by five key EAOPs, i.e., anodic oxidation (AO), anodic oxidation with electrogenerated H 2 O 2 (AO-H 2 O 2 ), electro-Fenton (EF), photoelectro-Fenton (PEF) and solar photoelectro-Fenton (SPEF), alone and in combination with other methods like biological treatment, electrocoagulation, coagulation and membrane filtration processes. Fundamentals of each EAOP are also given.

Electrochemical advanced oxidation processes: A review on their application to synthetic and real wastewaters

A critical review on textile wastewater treatments: Possible approaches.

The increase in the disposal of refractory organics demands for newer technologies for the complete mineralization of these wastewaters. Advanced oxidation processes (AOPs) constitute a promising technology for the treatment of such wastewaters and this study presents a general review on such processes developed to decolorize and/or degrade organic pollutants. Fundamentals and main applications of typical methods such as Fenton, electro-Fenton, photo-Fenton, sono-Fenton, sono-photo-Fenton, sono-electro-Fenton and photo-electro-Fenton are discussed. This review also highlights the application of nano-zero valent iron in treating refractory compounds.

A review on Fenton and improvements to the Fenton process for wastewater treatment

Advanced oxidation of phenol: A comparison between Fenton, electro-Fenton, sono-electro-Fenton and photo-electro-Fenton processes

Removal of phenol by heterogenous photo electro Fenton-like process using nano-zero valent iron

The present work focuses on the performance of Fenton, sono-Fenton, and sono-photo-Fenton processes for the oxidation of phenol present in aqueous solution. The effects of H 2 O 2 concentration, Fe 2+ concentration, pH, and initial phenol concentration on the oxidation of phenol were studied. The optimum Fe 2+ and H 2 O 2 concentrations for the Fenton process were 45 and 800 mg/L, respectively. For the sono-Fenton process, the optimum Fe 2+ and H 2 O 2 concentrations were 30 and 800 mg/L. respectively. The optimal conditions for the sono-photo-Fenton process were found to be 20 mg/L of Fe 2+ and 700 mg/L of H 2 O 2 . The optimum pH was found to be 3 for the processes investigated in the present study. The analysis of results showed that the sono-photo-Fenton method reduced the Fe 2+ concentration by 30-50% and the H 2 O 2 concentration by 12.5%. It was found that the sono-photo-Fenton technique showed better performance than the Fenton and sono-Fenton processes for the oxidation of phenol. A lumped kinetic model was used to predict the chemical oxygen demand reduction and the model was found to fit the data.

Degradation of Phenol in Aqueous Solution by Fenton, Sono‐Fenton and Sono‐photo‐Fenton Methods

This study presents the degradation of phenol by the photoelectro-Fenton method using nano zero-valent iron (nZVI) immobilized in polyvinyl alcohol–alginate beads. The effect of nZVI loading, H2O2 concentration, pH, and initial phenol concentration on phenol degradation and chemical oxygen demand reduction was studied. The scanning electron microscope images of the nZVI beads were used to analyze their morphology, and their diameters were in the range of 500–600 μm. The concentration of nZVI in the beads was varied from 0.1 to 0.6 g/L. Fe2+ leakage of 1 and 3 % was observed with 0.5 and 0.6 g/L of nZVI, respectively, and the observed beads' fracture frequency was 2 %, which confirmed the stability of the beads. The optimum operating conditions that arrived for better degradation were 0.5 g/L of nZVI, pH 6.2, and 400 mg H2O2/L. The treatment of effluent by this method increased the biodegradability index of the effluent, and the degradation data were found to follow pseudo first-order kinetics.

Arjunan Babuponnusami

Papers

A review on Fenton and improvements to the Fenton process for wastewater treatment

Advanced oxidation of phenol: A comparison between Fenton, electro-Fenton, sono-electro-Fenton and photo-electro-Fenton processes

Removal of phenol by heterogenous photo electro Fenton-like process using nano-zero valent iron

Degradation of Phenol in Aqueous Solution by Fenton, Sono‐Fenton and Sono‐photo‐Fenton Methods

Treatment of phenol-containing wastewater by photoelectro-Fenton method using supported nanoscale zero-valent iron