Electrochemical synthesis of chemicals and treatment of wastewater promoted by salinity gradients using reverse electrodialysis and assisted reverse electrodialysis

In the last years, an increasing attention has been devoted to the utilization of waters with different salt content to drive valuable redox processes at the electrodes by reverse electrodialysis processes (RED) or assisted RED (A-RED), thus allowing to significantly reduce the energetic costs associated to conventional electrolyses. In this review, the most relevant findings were presented and were critically discussed. The use of RED and A-RED for the synthesis of chemicals, the conversion of CO2, and the treatment of wastewater contaminated by organic and inorganic pollutants resistant to traditional biological processes was analyzed. The main advantages and disadvantages of these routes were commented, as well as the key points that should be addressed to favor the utilization on an applicative scale

Transesterification of rapeseed oil over acid resins promoted by supercritical carbon dioxide

The methanolysis of rapeseed oil catalyzed by commercial styrene-divinylbenzene macroporous acid resins was performed in a batch reactor at 100-140 \ub0C and 10-46 MPa to study the effect of supercritical carbon dioxide (scCO2) on the performances of the process. Reaction temperatures of 120-140 \ub0C were necessary to obtain high enough yields of fatty acid methyl esters. Upon addition of scCO2 faster transesterification kinetics was obtained also at the lowest investigated operating pressure (10-11 MPa), working in two fluid phase systems. Experiments performed changing the reaction time indicated that most of the esters were formed during the first 3 h. When the pressure was increased at 38-46 MPa, the fluid phases merged in a single one without significant modification of the performances of the process. The enhancement effect of scCO2 on the transesterification kinetics is tentatively discussed in terms of modification of the phase behaviour of the reaction system and swelling of the polymeric acid resin. \ua9 2010 Elsevier B.V. All rights reserved

Electrical power production from low-grade waste heat using a thermally regenerative ethylenediamine battery

Thermally regenerative ammonia-based batteries (TRABs) have been developed to harvest low-grade waste heat as electricity. To improve the power production and anodic coulombic efficiency, the use of ethylenediamine as an alternative ligand to ammonia was explored here. The power density of the ethylenediamine-based battery (TRENB) was 85 \ub1 3 W m2-electrode area with 2 M ethylenediamine, and 119 \ub14Wm2 with 3 M ethylenediamine. This power density was 68% higher than that of TRAB. The energy density was 478 Wh m3-anolyte, which was ~50% higher than that produced by TRAB. The anodic coulombic efficiency of the TRENB was 77 \ub1 2%, which was more than twice that obtained using ammonia in a TRAB (35%). The higher anodic efficiency reduced the difference between the anode dissolution and cathode deposition rates, resulting in a process more suitable for closed loop operation. The thermal-electric efficiency based on ethylenediamine separation using waste heat was estimated to be 0.52%, which was lower than that of TRAB (0.86%), mainly due to the more complex separation process. However, this energy recovery could likely be improved through optimization of the ethylenediamine separation process

Electrochemical incineration of oxalic acid in the presence of NaCl

Recent researches have demonstrated that electrochemical methods offer an attractive alternative to traditional routes for treating wastewaters containing toxic or/and refractory organic pollutants. The effectiveness of the electrochemical treatment depends on many factors including the presence in solution of specie able to act as mediators. In particular, the effect of chloride ions on the performances of the process has been the object of numerous researches. However, up to now, many practical and theoretical aspects about this argument are not completely clear. In the present work, the anodic incineration of oxalic acid (OA) in the presence of NaCl has been investigated with the aim of studying in a systematic way the influence of numerous parameters, such as the current density, the flow rate, the OA, the NaCl concentrations and the pH on the performances of the process and to individuate the optimal operative conditions. Oxalic acid was chosen as model substrate for its low reactivity toward anodic oxidation, which also results in an incomplete mineralization of more complex organics. Furthermore, the oxidation of this simple molecule does not involve the formation of stable intermediates thus giving rise to a more easy rationalizing of experimental results. Since the effect of NaCl on the process is expected to depend on the nature of the electrodic material, two very different anodes were used: the Ti/IrO2-Ta2O5 which presents a quite low oxygen overpotential and boron doped diamond (BDD) which is probably one of the more promising materials for the electrochemical incineration

Electrochemical remediation of phenol contaminated kaolin under low-strength electric fields

Soil degradation is a global concern. Electrochemical remediation (ER) technology is considered an appealing strategy for soil remediation because it is a low-cost, adaptable, and effective noninvasive in situ technology. Currently, the remediation of soil characterized by fine grains, low-hydraulic permeability, heterogeneous conditions, and mixtures of contaminants is still challenging since other conventional technologies are poorly effective. ER of soil is based on the application of low potentials between a couple of electrodes which induces an electric field (E) in the contaminated field. In this work, very low values of electric field (E ≤ 0.25 V cm−1) were used for the ER of contaminated kaolin. Phenol was selected as model hazardous organic compound and kaolin as model, reproducible and low buffering and low permeability clay. The effect of several factors, including the nature of the electrodes, treatment time, kind of current, the strength of the E and the nature of supporting electrolyte, on the performance of the process was investigated in detail and discussed in terms of the normalized phenol concentration and its total removal from the kaolin. Overall, the main finding is that the use of very low value of E (0.15 V cm−1) can allow to simultaneously desorb, mobilize and also in-situ degrade phenol. The highest removals of phenol up to approximately 80% and 90% from the kaolin under both direct and sinusoidal E, respectively, were reached using compact graphite as electrodes in presence of Na2SO4 into the kaolin

A critical review on latest innovations and future challenges of electrochemical technology for the abatement of organics in water

Updated water directives and ambitious targets like the United Nations’ Sustainable Development Goals (SDGs) have emerged in the last decade to tackle water scarcity and contamination. Although numerous strategies have been developed to remove water pollutants, it is still necessary to enhance their effectiveness against toxic and biorefractory organic molecules. Comprehensive reviews have highlighted the appealing features of the electrochemical technologies, but much progress has been made in recent years. In this timely review, a critical discussion on latest innovations and perspectives of the most promising electrochemical tools for wastewater treatment is presented. The work describes the performance of electrocatalytic anodes for direct electrochemical oxidation, the oxidation mediated by electrogenerated active chlorine, the electrocatalytic reduction as well as coupled approaches for synchronous anodic and cathodic processes combined with homogeneous and heterogeneous catalysis. The last section is devoted to the assessment of scale-up issues and the increase in the technology readiness level

Electrochemical remediation of kaolin-soil contaminated by phenol: effect of several operative parameters

Electrochemical remediation technology is considered an appealing strategy for the remediation of fine- grained soils, characterized by a low hydraulic conductivity and large specific surface area, contaminated with inorganic, organic, and mixed pollutants. In both Electrokinetic (EK) and Electrochemical Geo-Oxidation (ECGO) technologies, an electric field is imposed on the contaminated soil to remove the pollutants by the combined mechanisms of electroosmosis, electromigration, and/or electrophoresis. Moreover, ECGO uses low voltage and both direct and alternating amperage (DC/AC) applied in a proprietary series to induce reduction-oxidation reactions on soil surfaces at the micro-scale. According to the literature, in this method, each soil particle acts as a micro-capacitor that charges and discharges in a cyclic fashion. The energy burst on discharge at the micro-scale is intense, theoretically allowing the conversion of most organic contaminants to carbon dioxide and water near the conducting particle surface [2-4]. However, the effectiveness of the technology strongly depends on the physical-chemical states of the soils and the contaminants, pH, sorption of contaminants on soil particle surfaces and different effects induced by the hydrogen ions and hydroxide ions generated at the electrodes. In this work, the effect of several factors, including the intensity and mode of the applied electric field, duration of treatment, nature of supporting electrolytes, on the electrochemical remediation of kaolin-soil contaminated by phenol (200 mgPhenol/kgsoil) was investigated. It was found that a proper selection of the operative parameters is the key- factor to improve the electrochemical remediation of the contaminated soil. High removal of phenol from the kaolin up to 88% was achieved after 93 hours of treatment using graphite electrodes and a gradient electric field of 0.15 V cm-1. [1] A. T. Yeung et al. J. Hazard. Mater. 2011, 195, 11 [2] D. Rahner et al. Electrochim. Acta 2002, 47, 1395 [3] J. Röhrs et al. Electrochim. Acta 2002, 47, 1405 [4] L.M. Zanko et al. Electrochim. Acta 2020, 354, 13669

The influence of sludge retention time on mixed culture microbial fuel cell start-ups

In this work, the start-ups of air-cathode microbial fuel cells (MFCs) seeds with conventional activated sludge cultivated at different solid retention times (SRTs) are compared. A clear influence of the SRT of the inoculum was observed, corresponding to an SRT of 10 days to the higher current density exerted, about 0.2 A m 122. This observation points out that, in this type of electrochemical device, it is recommended to use high SRT seeds. The work also points out that in order to promote an efficient start-up, it is not only necessary to use high SRT seeds, but also to feed a high COD concentration. When feeding 10,000 ppm COD and keeping SRT of 10 d differences of current densities up to 0.1 A m 122 were observed within a cycle. Additionally it was observed that SRT influences direct and indirect electron transfer mechanisms, being the direct mechanisms the most relevant ones, accounting for more than 95% of the total electricity production