Electrochemical degradation of surfactants in domestic wastewater using a DiaClean® cell equipped with a boron-doped diamond electrode

Abstract

Treating domestic wastewater has become more and more complicated due to the high content of different types of detergents. In this context, advanced electro-oxidation (AEO) has become a powerful tool for complex wastewater remediation. The electrochemical degradation of surfactants present in domestic wastewater was carried out using a DiaClean® cell in a recirculation system equipped with boron-doped diamond (BDD) as the anode and stainless steel as the cathode. The effect of recirculation flow (1.5, 4.0 and 7.0 L min−1) and the applied current density (j = 7, 14, 20, 30, 40, and 50 mA cm−2) was studied. The degradation was followed by the concentration of surfactants, chemical oxygen demand (COD), and turbidity. pH value, conductivity, temperature, sulfates, nitrates, phosphates, and chlorides were also evaluated. Toxicity assays were studied through evaluating Chlorella sp. performance at 0, 3, and 7 h of treatment. Finally, the mineralization was followed by total organic carbon (TOC) under optimal operating conditions. The results showed that applying j = 14 mA cm−2 and a flow rate of 1.5 L min−1 during 7 h of electrolysis were the best conditions for the efficient mineralization of wastewater, achieving the removal of 64.7% of surfactants, 48.7% of COD, 24.9% of turbidity, and 44.9% of mineralization analyzed by the removal of TOC. The toxicity assays showed that Chlorella microalgae were unable to grow in AEO-treated wastewater (cellular density: 0 × 104 cells ml−1 after 3- and 7-h treatments). Finally, the energy consumption was analyzed, and the operating cost of 1.40 USD m−3 was calculated. Therefore, this technology allows for the degradation of complex and stable molecules such as surfactants in real and complex wastewater, if toxicity is not taken into account.

Step-by-step guide for electrochemical generation of highly oxidizing reactive species on BDD for beginners

“…BDD is a “non-active” electrode when acting as an anode, and the HORS that are generated when a high oxidation overpotential is applied do not drastically change their chemical nature; this property makes it a unique material and is the basis for a large number of applications including in the area of environmental remediation ( Sánchez-Montes et al, 2020 ; Carrera-Cevallos et al, 2021 ; Cisneros-León et al, 2023 ; Long et al, 2023 ). Therefore, studying the surface terminations of the crystal lattice of this material becomes key and is addressed in this section.…”

“…For water treatment, electrochemical oxidation can take advantage of the complexity of mixtures of organic and inorganic species that can be found in typical contaminated water since, depending on the composition of the inorganic electrolyte in the system to be treated, the so-called HORS can be generated ( Wen et al, 2017 ; Xu et al, 2021 ; Ahmed et al, 2022 ; Parvulescu et al, 2022 ; dos Santos et al, 2023 ; Mousset, 2023 ). Most HORS are “free” radicals and detrimental to most biological systems; the opposite is true for advanced oxidation processes, where they contribute to the oxidation of organic and inorganic matter ( Murphy et al, 2022 ; Cisneros-León et al, 2023 ). HORS covers a wide spectrum of inorganic radicals, ions, and neutral molecules in aqueous media whose redox potentials are varied ( Ross and Neta, 1982 ; Armstrong et al, 2015 ).…”

“…It is a non-active electrode; i.e., its chemical structure is not compromised by the redox processes to which it may be subjected, although its reticular terminations are susceptible to slight changes during oxidation and reduction (Berenguer et al, 2019). As it has a very wide potential, this electrode has been used for multiple applications in electroanalytical chemistry (Wei et al, 2011b;Joshi et al, 2022), electrosynthesis (Ivandini and Einaga, 2017;Lips and Waldvogel, 2019), and AEO for water treatment (Cisneros-León et al, 2023).…”