This paper analyzes the advantages and drawbacks of the combination of UV irradiation with electrolysis with the aim to give insight about the feasibility of the application of this technology for the reclaiming of conventionally-treated wastewater. The oxidation of synthetic solutions containing five selected model complex pollutants has been compared, showing that UV irradiation improves the results of electrolysis for progesterone, metoprolol and caffeine and deteriorates the performance for the degradation of sulfamethoxazole and dimethyl-phthalate. Differences observed becomes lower when mineralization is compared showing that the effects of UV irradiation are diluted when a mixture of species is oxidized. Results suggest that high ThOD/TOC (Theoretical Oxygen Demand/Total Organic Carbon) ratios improve the synergistic coupling of technologies while low values lead to a clear antagonistic effect. Because during oxidation progress this ratio is decreased, the observed effect on mineralization is much lower than in the oxidation of the raw molecule. Opposite to this low effect on the oxidation of organics, the improvement in the performance of the disinfection by coupling UV to electrolysis is much clearer. In addition, UV irradiation modifies significantly the chlorine speciation and helps to prevent the formation of hazardous species such as chlorate and perchlorate during the electrochemical processes.

In this work, a novel integrated electrochemical process for urban wastewater regeneration is described. The electrochemical cell consists in a Boron Doped Diamond (BDD) or a Dimensionally Stable Anode (DSA) as anode, a Stainless Steel (SS) as cathode and a perforated aluminum plate, which behaves as bipolar electrode, between anode and cathode. Thus, in this cell, it is possible to carry out, at the same time, two different electrochemical processes: electrodisinfection (ED) and electrocoagulation (EC). The treatment of urban wastewater with different anodes and different operating conditions is studied. First of all, in order to check the process performance, experiments with synthetic wastewaters were carried out, showing that it is possible to achieve a 100% of turbidity removal by the electrodissolution of the bipolar electrode. Next, the effect of the current density and the anode material are studied during the ED-EC process of actual effluents. Results show that it is possible to remove Escherichia coli and turbidity simultaneously of an actual effluent from a WasteWater Treatment Facility (WWTF). The use of BDD anodes allows to remove the E. coli completely at an applied electric charge of 0.0077 A h dm(-3) when working with a current density of 6.65 A m(-2). On the other hand, with DSA anodes, the current density necessary to achieve the total removal of E. coli is higher (11.12 A m(-2)) than that required with BDD anodes. Finally, the influence of cell flow path and flow rate have been studied. Results show that the performance of the process strongly depends on the characteristics of the initial effluent (E. coli concentration and Cl(-)/NH(4)(+) initial ratio) and that a cell configuration cathode (inlet)-anode (outlet) and a higher flow rate enhance the removal of the turbidity from the treated effluent.

This work presents an integrated electrodisinfection/electrocoagulation (ED-EC) process for urban wastewater reuse that employs iron bipolar electrodes. Boron doped diamond (BDD) was used as the anode and stainless steel (SS) as the cathode. A perforated iron plate was introduced between the anode and cathode to function as a bipolar electrode. This ED-EC combined cell makes it possible to conduct the simultaneous removal of microbiological content and elimination of turbidity from urban wastewater. The results show that current densities greater than or equal to 6.70 A m(-2) enable complete disinfection of the effluent and the removal of more than 90% of its initial turbidity. Hypochlorite and chloramines formed during the ED-EC process were found to be the main compounds responsible for the disinfection process. Furthermore, a cell configuration of cathode (inlet)-anode (outlet) improves the process performance by enhancing turbidity removal. Finally, the influence of the bipolar electrode material (iron or aluminium) was assessed. The results indicate that the efficiency of the electrodisinfection process depends mainly on the anodic material and is not influenced by the material of the bipolar electrode. In contrast, the removal of turbidity is more efficient when using iron as a bipolar electrode, especially at low current densities, due to the formation of a passive layer on the aluminium that hinders the dissolution of the bipolar electrode.

In recent years, thousands of scientific articles have considered the application of electrochemical technologies to remediate environmental problems ranging from the treatment of polluted soils to the removal of hazardous species from industrial liquid wastes. New research topics continue to emerge. Despite such research efforts, the technology readiness level (TRL) for many of those technologies remains very low; although most are considered promising, many are far from being introduced as efficient processes into the market. Important barriers need to be overcome to reach high TRLs. Some of these are scientific or technological and generate the opportunity for critical, applied research. Others are related to the lack of components in the value chain of the technology and generate opportunities for entrepreneurs to benefit from an improvement in the TRL. In this short review, a brief description of the current state of the most relevant technologies which are still in low TRL is carried out, highlighting barriers that must be removed to achieve full-scale applications in industry.

This work focused on the removal of persistent organic pollutants (POPs) from wastewater using irradiation-assisted electrochemical technologies, i.e. sonoelectrolysis, photoelectrolysis and sono-photoelectrolysis. Single-irradiation processes (sonolysis and photolysis) and electrochemical oxidation using conductive diamond anodes (current density of 30 mA cm -2 ) were also evaluated for comparison. Three POPs with different molecular structures (sulfamethoxazole, metoprolol and caffeine, initial concentration of 100 mg dm -3 ) were studied to evaluate the robustness of the selected technologies and the oxidation mechanisms involved in each case. Results show that the single application of the irradiation technologies led to the removal of only a small amount of POPs and no mineralisation, with the nature of the pollutant showing a marked effect; the opposite was observed for the single application of conductive diamond electrochemical oxidation (CDEO), which is a highly robust and efficient technology for the degradation of all types of POPs. Sonoelectrolysis, photoelectrolysis and sono-photoelectrolysis processes (ultrasound conditions: 200 W, ultraviolet conditions: 254 nm, 4 W) may show synergistic, antagonistic or nil effects with respect to a single electrochemical oxidation event, depending on the nature of the treated molecule. The differences observed may be related to the different chemical nature of the organic species studied, indicating an important role of mediated oxidation processes, which may be enhanced with ultrasounds and ultraviolet radiation techniques.

This work focuses on the application of electrolysis with carbon felt cathodes for the reclamation of actual effluents from municipal wastewater treatment facilities (WWTFs) in combination with different anode materials (dimensionally stable anodes-DSA, conductive diamond anodes-CDA and iron-Fe). First of all, the efficiency of electrodisinfection with CDA and DSA was assessed, finding that total elimination of Escherichia coli (E. coli) can be attained at applied electric charges below 0.03 Ah dm-3 , and that the disinfection process is more efficient when using CDA. Furthermore, it was observed that the formation of hydrogen peroxide on carbon felt cathodes limits the concurrence of disinfection by-products (chlorates, perchlorates and organic chlorinated by-products), an interesting result that broadens the potential of CDA for the regeneration of urban wastewater. Results with Fe anodes show that it is possible to attain the complete removal of microorganisms with comparable efficiency to that of CDA (due to the contribution of Fenton's reaction) and that it was possible to totally remove the turbidity of the effluent when working at current densities from 12.50 A m-2. Finally, it was found that Fe is the most efficient anode material (lowest power consumption) at low current densities and CDA is the most appropriate one at current densities higher than 5 A m-2. According to these results, the pairs anode-cathode CDA-carbon felt and Fe-carbon felt behave as the most promising electrode materials to be applied in wastewater reclamation processes.

No abstract

In this work, the removal of Procion Red MX-5B dye by electrochemical oxidation with boron doped diamond (BDD) anodes was investigated. The impact of current density, flow rate, initial pH, and supporting electrolyte was evaluated on dye and organic matter removal. Furthermore, the use of dimensionally stable anodes (DSA) was tested to evaluate process performance. Results show that after 240 minutes, it is possible to achieve full dye and COD (chemical oxygen demand) removal, regardless of applied current density. This is due to the generation of powerful oxidantsi.e. hydroxyl radicals and peroxodisulfate-, which attack the organic matter in the wastewater, promoting its complete degradation. However, process efficiency increases when using lower current densities (10 mA cm-2): electric charges of about 5 Ah dm-3 are sufficient to fully remove both dye and COD, while charges higher than 15 Ah dm-3 are required when working at higher current densities (> 30 mA cm-2). This fact is related to the production of large amounts of hydroxyl radicals, which are wasted in other reactions at higher current densities. On the other hand, higher flow rates (300 dm 3 h-1) promote Procion Red MX-5B and organic matter degradation, due to improved mass transfer within the system. Regarding the impact of initial pH on dye removal, no significant differences were observed. Conversely, COD is clearly affected by this parameter: it is only possible to fully remove the organic matter when working at natural pH. Finally, with DSA anodes, higher dye removal efficiencies are attained than with BDD electrodes, when 100 mg dm-3 chlorides are added to the supporting electrolyte. Likewise, higher chloride concentration (100-1000 mg dm-3) was observed to enhance process efficiency when using DSA as anode material. However, during electrolysis with both BDD and DSA, chloride ions in the supporting electrolyte promote the production of 3 intermediate organochlorinated compounds. Therefore, under these conditions, no full organic matter removal can be achieved, regardless of the anode material employed.