Improving the Treatment Efficiency and Lowering the Operating Costs of Electrochemical Advanced Oxidation Processes

Influence of Water Hardness and Complexing Agents on Electrochemical Hydrogen Peroxide Generation

Recently, many studies have been published regarding electrochemical oxygen reduction reaction for generating hydrogen peroxide (H2O2) using gas diffusion electrodes (GDEs) for various applications. Sodium salts solved in deionized water were usually used as supporting electrolytes. In technical applications, however, tap water-based electrolytes with hardeners are particularly relevant and have only been considered in a few studies to date. In this work, we investigated the influence of hardeners on H2O2-generation at 150 mA cm-2 and were able to show that scaling occurs predominantly on the GDE-surface and not in its pore structure. With the novel method in electrochemical synthesis by using complexing agents to bind hardeners, we were able to significantly reduce the scaling. Even after 10 h of operation, the reactor still achieves a faradaic efficiency (FE) of above 70 % (>67 mg h-1 cm-2), comparable to the experiments without hardeners and complexing agents in the electrolyte. Furthermore, we demonstrate that the complexing agents are not electrochemically converted at the carbon-based GDE and behave inertly. If the cell is operated with complexing agents and rinsed with acidic liquid (anolyte) between batches, scaling can be completely avoided.

Removal of pharmaceuticals and personal care products from wastewater via anodic oxidation and electro-Fenton processes: current status and needs regarding their application

This review provides a current opinion on the most recent works that have been published toward the application of electrochemical advance oxidation processes (EAOPs) for the degradation of pharmaceutical and personal care products (PPCPs) in water streams. Advances in the application of anodic oxidation (AO)- and electro-Fenton (EF)-based processes are reported, including operational conditions, electrode performance, and removal. Although AO- and EF-based processes can easily reach 100% removal of PPCPs, mineralization is desirable to avoid the generation of potential toxic byproducts. The following section exploring some techno-economic aspects of the application of EAOPs is based on electrode selection, operational costs as well as their use as cotreatments, and their synergistic effects. Finally, this short review ends with perspectives about the emerging topics that are faced by these technologies applied for the degradation of PPCPs in research and practice.

Treatment of petroleum hydrocarbon contaminated soil by combination of electro-Fenton and biosurfactant-assisted bioslurry process

Removing petroleum hydrocarbons (PHCs) from polluted soil is challenging due to their low bioavailability and degradability. In this study, an experiment was carried out to treat soil polluted with petroleum hydrocarbon using a hybrid electro-Fenton (with BDD anode electrode) and biological processes stimulated with long-chain rhamnolipids (biosurfactants). Electro-Fenton treatment was applied as a pretreatment before the biological process to enhance PHC biodegradability, which would benefit the subsequent biological process. The effects of initial pH, hydroxide concentration, soil organic matter composition, PHCs intermediates during the electro-Fenton process, and total numbers of bacteria in the biological process were analyzed to determine the optimum conditions. The results showed that the optimized electrolysis time for the electro-Fenton was 12 h. The change induced during pretreatment at a specified time was found suitable for the biological process stage and led to 93.6% PHC degradation in combination with the electro-Fenton-and-biological process after 72 h. The combined system's performance was almost 40% higher than individual electro-Fenton and biological treatments. GC-MS analysis confirms the formation of 9-octadecen-1-ol (Z), 2-heptadecene, 1-nonadecene, 1-heneicosene, and pentacosane as fragmentation during the PHCs degradation process. Thus, the electro-Fenton process as pretreatment combined with a biological process stimulated with rhamnolipids (biosurfactants) could be effectively applied to remediate soil polluted with PHCs. However, the system needs further research and investigation to optimize electrolysis time and biosurfactant dose to advance this approach in the soil remediation process.

PbO2 modified BDD electrode by dicationic ionic liquids assisted electrodeposition for efficient electrocatalytic degradation of pesticide wastewater

Pesticide wastewater is difficult to treat, and it is necessary to develop a new anode material electrochemical oxidation to efficiently degrade pesticide wastewater. DIL-PbO₂-Ti/BDD electrodes with better electrocatalytic oxidation performance were obtained by using dicationic ionic liquid (DIL) for assisted electrodeposition of PbO₂ modified boron-doped diamond (BDD) electrodes. At a current density of 100 mA cm^-2 and a temperature of 25 °C, the DIL-PbO₂-Ti/BDD electrode was used as anode and titanium plate as cathode. The electrochemical window and oxygen evolution potential (OEP) of the DIL-PbO₂-Ti/BDD electrode obtained by CV testing at a scan rate of 50 mV s^-1 in 1 M H₂SO₄ were 4.12 and 3.29 V, respectively. Under the conditions of current density of 100 mA cm^-2, 25 °C, pH 12, salt content of 8%, chemical oxygen demand (COD) of 24,280.98 mg L^-1, and total nitrogen (TN) content of 5268 mg L^-1, after electrification for 12 h, the removal efficiency of COD and TN reached 64.88 and 67.77%, respectively, indicating that the DIL-PbO₂-Ti/BDD electrode has excellent electrocatalytic performance. In order to further understand the mechanism of electrochemical degradation of pesticide wastewater, HPLC-MS was used to detect the intermediates in the degradation process, and the possible degradation pathways were proposed in turn.

Combined Electrocoagulation and Physicochemical Treatment of Cork Boiling Wastewater

Cork boiling wastewater (CBW) is a highly polluted and difficult to treat effluent resultant from the cork manufacturing industry. This study aims to evaluate a new, reliable, efficient, and sustainable process to treat this effluent. This paper tested electrocoagulation as a pre- and post-treatment to improve the already existing physicochemical treatment in a cork production facility in Portugal. In the physicochemical procedures (PC), the addition of different volumes of coagulant (ferric chloride (III) 40% w/w), neutralizer (sodium hydroxide, 32% w/w), and flocculant (polyacrylamide, 0.2 g/L) were evaluated. Electrocoagulation (EC) was performed in a bench-scale reactor, using aluminum and stainless-steel electrodes. For EC, different initial pH, current density, and current tension values were tested. When electrocoagulation was used as a post-treatment, better performances were achieved. However, treatment costs were increased significantly. Coagulation/flocculation offers a viable and cheap treatment, achieving removal efficiencies of 88.2%, 81.0%, 76.9%, and 94.2% for total chemical oxygen demand (tCOD), total carbon (TC), total nitrogen (TN), and soluble chemical oxygen demand (sCOD), respectively. With a PC-EC combination, it is possible to achieve removal efficiencies of 92.4%, 88.0%, 91.4%, and 91.4% for tCOD, TC, TN, and sCOD, respectively. The increased TN removal efficiency can translate into great benefits for certain discharge conditions and should be taken into consideration for improving the sustainability of cork industry. On the other hand, when EC is used as a pre-treatment, there are no benefits either in terms of treatment performance or operating costs.