Biodiesel Production From Waste Cooking Oil: A Study Towards Zero‐Discharge Strategy via Pilot‐Scale Packed Adsorption Column for Wash Water Treatment and Reuse

Food-waste-derived-activated carbon offers a sustainable solution for treating alkaline, oil-rich biodiesel wash water. In order to assess its viability in pilot-scale biodiesel production, the physicochemical characterization of waste cooking oil (WCO), which included FFA (0.11 to 1.77%), moisture content (0.69 to 1.87%), viscosity (13.01 to 16.76 cSt), and density (0.910 to 0.94 g/cc). Low-FFA waste cooking oil was converted into biodiesel by single-step transesterification at 60°C-65°C utilizing a methanol-NaOH. Biodiesel was washed with hot water until a neutral pH was reached, producing 128-136 L of alkaline wash water each batch. Biodiesel wash water with high pH (10.9 to 11.7), turbidity (441 to 420 NTU), TSS (18.88 to 18.19 mg/L), TDS (84-88 mg/L), oil and grease (1.24 to 0.918 mg/L) concentration was targeted for recovery and reuse by adsorption utilizing food waste-activated carbon. In order to effectively recover and reuse in a zero-liquid-discharge process, a pilot-scale packed adsorption column utilizing mixed food waste-activated carbon was included into the biodiesel system to treat 128-136 L of alkaline, high-turbidity wash water each batch. Effective water purification was demonstrated by the treatment of mixed biodiesel wash water in the food waste-activated carbon (FWAC) column, which consistently lowered pH to ~7.1-7.3, turbidity to 1 NTU, TSS to 9-10 mg/L, and oil-grease to 0.15-0.17 mg/L. Fuel satisfying ASTM criteria was created by refining biodiesel using FWAC-treated wash water, showcasing a successful zero-discharge strategy that promotes the circular economy, GHG reduction, and India's Net Zero 2070 goal.