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

Hybrid process combining ultrafiltration and electro-oxidation for COD and nonylphenol ethoxylate removal from industrial laundry wastewater

Laundry wastewater is a significant source of nonylphenol ethoxylate (NPEO) at wastewater treatment plants, where its breakdown forms persistent nonylphenol (NP). NP poses risks as an endocrine disruptor in wildlife and humans. This study investigates the degradation of NPEO and COD in industrial laundry wastewater (LWW) using a two-stage process combining ultrafiltration (UF) and electro-oxidation (EO). UF was used to remove suspended solids, while soluble COD (COD0 = 239 ± 6 mg.L-1) and NPEO (NPEO0 = 341 ± 8 μg.L-1) were oxidized by the EO process. Different operating parameters were studied such as current density, electrolysis time, type of cathode and supporting electrolyte concentration. Using an experimental design methodology, the optimal conditions for COD and NPEO3-17 degradation were recorded. This included achieving 97% degradation of NPEO3-17 and 61% degradation of COD, with a total operating cost of 3.65 USD·m-3. These optimal conditions were recorded at a current density of 15 mA cm-2 for a 120-min reaction period in the presence of 4 g·Na2SO4 L-1 using a graphite cathode. The EO process allowed for reaching the guidelines required for water reuse (NPEO <200 μg.L-1, COD <100 mg.L-1) in the initial laundry washing cycles. Furthermore, our results demonstrate that both NP and NPEO compounds, including higher and shorter ethoxylate chains (NPEO3-17), were effectively degraded during the EO process, with removal efficiencies between 94% and 98%. This confirms the EO process's capability to effectively degrade NP, the by-product of NPEO breakdown.

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

Selecting the ideal anodic potential conditions and corresponding limiting current density to generate reactive oxygen species, especially the hydroxyl radical (•OH), becomes a major challenge when venturing into advanced electrochemical oxidation processes. In this work, a step-by-step guide for the electrochemical generation of •OH on boron-doped diamond (BDD) for beginners is shown, in which the following steps are discussed: i) BDD activation (assuming it is new), ii) the electrochemical response of BDD (in electrolyte and ferri/ferro-cyanide), iii) Tafel plots using sampled current voltammetry to evaluate the overpotential region where •OH is mainly generated, iv) a study of radical entrapment in the overpotential region where •OH generation is predominant according to the Tafel plots, and v) finally, the previously found ideal conditions are applied in the electrochemical degradation of amoxicillin, and the instantaneous current efficiency and relative cost of the process are reported.