Treatment of wastewater from the flocculation process of waste cutting fluid by zerovalent iron catalyst

Abstract

Waste cutting fluids are considered as hazardous wastes because they contain numerous different components causing environmental problems. Normally, a flocculation method is applied to treat preliminarily. However, the output wastewater still needs treating further to meet the national standards of industrial wastewater before disposal. So, this research reports the secondary treatment stage of the waste cutting fluid collected from an industrial factory in Vietnam using zero valent iron (ZVI) catalyst. This catalyst was synthesized via a redox reaction between sodium borohydride (NaBH₄) and ferric chloride (FeCl₃). Key factors affecting the quality of the ZVI particles such as the concentration of the NaBH₄ reductant, reaction temperature, and dropping rate were investigated systematically. At the optimum synthesis conditions, viz. the NaBH₄ concentration of 0.2 M, reaction temperature of 25 ^oC and the dropping rate of 3 ml/min, the synthesized ZVI exhibited a narrow range of particle size distribution with a mean size of 3.9 μm, followed by a high surface area, and good catalytic activity. As a catalyst for secondary treatment of the waste cutting fluid, the synthesized ZVI demonstrated a moderate chemical oxygen demand (COD) removal performance of  49%, corresponding to COD reduction for from 4023 mg/l to about 2059 mg/l.