Photo-assisted electrochemical advanced oxidation processes for the disinfection of aqueous solutions: A review

Abstract

Disinfection is usually the final step in water treatment and its effectiveness is of paramount importance in ensuring public health. Chlorination, ultraviolet (UV) irradiation and ozone (O 3 ) are currently the most common methods for water disinfection; however, the generation of toxic by-products and the non-remnant effect of UV and O 3 still constitute major drawbacks. Photo-assisted electrochemical advanced oxidation processes (EAOPs) on the other hand, appear as a potentially effective option for water disinfection. In these processes, the synergism between electrochemically produced active species and photo-generated radicals, improve their performance when compared with the corresponding separate processes and with other physical or chemical approaches. In photo-assisted EAOPs the inactivation of pathogens takes place by means of mechanisms that occur at different distances from the anode, that is: (i) directly at the electrode’s surface (direct oxidation), (ii) at the anode’s vicinity by means of electrochemically generated hydroxyl radical species (quasi-direct), (iii) or at the bulk solution (away from the electrode surface) by photo-electrogenerated active species (indirect oxidation). This review addresses state of the art reports concerning the inactivation of pathogens in water by means of photo-assisted EAOPs such as photo-electrocatalytic process, photo-assisted electrochemical oxidation, photo-electrocoagulation and cathodic processes. By focusing on the oxidation mechanism, it was found that while quasi-direct oxidation is the preponderant inactivation mechanism, the photo-electrocatalytic process using semiconductor materials is the most studied method as revealed by numerous reports in the literature. Advantages, disadvantages, trends and perspectives for water disinfection in photo-assisted EAOPs are also analyzed in this work.

Hydrodehalogenation of Polychloromethanes on Silver‐Based Gas Diffusion Electrodes

“…In the last thirty years, the removal of halogen groups from organic substrates has gained a strong attention due to the possibility of applying this process for environmental purposes, [5–12] being more effective than the most popular electrooxidative process of total degradation. The interest in oxidative processes is confirmed by recent reviews [13–20] and different papers on the mineralization of chlorophenoxy herbicides, [21–23] mono‐ and poly‐halogenated phenolic wastes, [24–26] and other chlorinated organic compounds [27–29] . Oxidative electrochemical processes are more widely used and studied because these treatments can lead to the total degradation (mineralization) of the compounds [16,17] .…”

Floating Carbon-Doped TiO2 Photocatalyst with Metallic Underlayers Investigation for Polluted Water Treatment under Visible-Light Irradiation

“…One of the problems is that clean freshwater makes up only a small fraction of all water resources and they are unevenly distributed across the globe. Following the data presented by the World Health Organization, more than 2 billion people lack sanitation services and a huge part of them live in an area plagued by freshwater shortages [1]. The increasing scarcity of clean freshwater is the result of industrial growth, advanced manufacturing, increased water contamination and climate change as well as poor water treatment and insufficient disinfection [2].…”

“…Conventional water treatment technologies, such as biological treatment, chemical precipitation, membrane filtration, and chlorination have been proposed in order to solve this issue [1,2,4]. However, in some cases these techniques lack effectiveness, particularly in the decomposition of microorganisms (bacteria, viruses, fungi, and etc.)…”

“…AOPs are characterised by the in-situ generation of reactive oxygen species (ROS), especially superoxide anion (•O 2 − ) and hydroxyl radicals (•OH) which act as powerful oxidising agents capable of decomposing various organic compounds [2]. The oxidation power of hydroxyl radicals (oxidation potential 2.8 V) is higher than chlorine (oxidation potential 1.36 V) and even ozone (oxidation potential 2.07 V) [1]. There are various types of AOPs including the Fenton process [11], electrochemical oxidation [12], photocatalysis [13], electrical discharge [14], catalytic ozonation [15,16], sonolysis [17], or wet air oxidation [18].…”

Influence of the Metabolic Activity of Microorganisms on Disinfection Efficiency of the Visible Light and P25 TiO2 Photocatalyst

“…In contact with water molecules and dissolved oxygen, excited charges generate reactive oxygen species (ROS), that are universal oxidants and can neutralize various contaminants to form neutral compounds [4]. In comparison to the traditional wastewater treatment methods like UV irradiation and chlorination, photocatalytic water treatment has superior oxidation power [5], does not form carcinogenic disinfection by-products [6], and can be used for the treatment of pathogens which are resistant to chlorine [7].…”