Enhanced recalcitrant metalworking fluid remediation via hybrid systems integrating nano zero-valent iron, biodegradation, and adsorption processes

Metalworking fluids (MWFs) pose a significant challenge in industrial wastewater treatment due to their toxicity, pollution load, and recalcitrance. Therefore, developing more sustainable and efficient degradation technologies is critical to mitigate environmental hazards and threats to ecosystems. In this study, three treatment methods - nanoscale zero-valent iron (nZVI), biodegradation, and adsorption were investigated in different combinations for sustainable disposal of waste MWF with initial chemical oxygen demand (COD) concentrations of 11,950 mg/L and 50,000 mg/L. The three treatment methods were integrated sequentially into two Hybrid Systems (Hybrid System 1 - nZVI, biological treatment and adsorption, and Hybrid System 2 - biological treatment, nZVI and a final biological step) treatment protocols. The focus was to compare their treatment performance in terms of COD removal efficiency and toxicity reduction. The results demonstrate that Hybrid System 1 was superior in terms of COD removal efficiency, achieving removal rates of 93.94 % and 70.01 % for MWF at initial COD concentrations of 11,950 mg/L and 50,000 mg/L, respectively. Both hybrid treatment systems exhibited comparable toxicity reduction performance for MWF with an initial COD concentration of 11,950 mg/L, the effluent registering low toxicity, while for MWF with an initial COD concentration of 50,000 mg/L, toxicity was reduced by 86 %. These findings indicate that Hybrid System 1 holds significant potential for treating highly toxic and recalcitrant industrial wastewater.