Three-Dimensional Electrolysis Reactor Using Automotive Scrap Metals for the Treatment of Water-Soluble Cutting Fluid Solution

This study investigated the efficacy of electrochemical treatment of a water-soluble cutting fluid (SCF) solution using Al, Fe, and stainless steel (SUS304) scraps as three-dimensional (3D) electrode packing materials. The SCF solution had an initial CODCr of approximately 109,000 mg·L−1, a TOC of approximately 25,000 mg·L−1, and an initial pH of 9.65. During treatment, the pH remained in the alkaline range (9.99–10.67), and the solution conductivity was approximately 1000 μS·cm−1. Using a conventional two-dimensional (2D) configuration, Al exhibited the highest removal efficiencies (TOC: 58.55%; CODCr: 57.12%). An applied current of 0.8 A, corresponding to a current density of 5.00 mA·cm−2 based on the geometric electrode area, and an inter-electrode distance of 40 mm provided an optimal balance between treatment performance and energy consumption. Under these optimized conditions, the introduction of metal scraps as 3D packing media significantly enhanced treatment efficiency. Al scrap (20 g) achieved the highest TOC removal (69.55%), while Fe scrap showed superior CODCr removal (87.42% at 40 g) with the lowest specific energy consumption (0.27 kWh·kg−1 CODremoved). The energy consumption of the baseline D system was 0.46 kWh·kg−1 CODremoved(cage O) and 0.72 kWh·kg−1 CODremoved(cage X). Overall, scrap-based 3D electrodes effectively improved organic removal and energy performance, demonstrating their potential as low-cost and sustainable electrode materials for the electrochemical pre-treatment of high-strength oily wastewater.