Abstract
<title>Abstract</title> <p>Laboratory waste liquids (LWL) contaminated with hexavalent chromium (Cr(VI)) constitute a hazardous waste stream that is commonly managed through off-site treatment and disposal services. This approach is costly and limits the implementation of on-site remediation technologies that could reduce waste management requirements. In this work, chitosan-supported zero-valent iron nanocomposites (nZVI@CS) were optimized, scaled up and evaluated for Cr(VI) removal in recirculating packed-bed columns. Different coagulation and crosslinking strategies using NaOH and sodium tripolyphosphate (TPP) were investigated, and their influence on structural stability, mechanical properties, and preservation of the α-Fe phase was assessed through capillary viscometry, dynamic mechanical analysis (DMA), X-ray diffraction (XRD), and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS). TPP incorporation increased the structural stability of the NCs but compromised the preservation of α-Fe by promoting iron oxidation. The optimized NCs were successfully applied as packing material in recirculating packed-bed columns. A 2³ factorial design showed that packing configurations, flow directions, and flow rate had no statistically significant effect on Cr(VI) removal within the investigated operating range. Although flow direction showed the greatest influence on cumulative removal capacity, upward-flow configurations achieved the best performance, reaching a maximum cumulative removal capacity of 22.4 mg Cr(VI) g⁻¹ nZVI after successive reuse cycles. The recirculating packed-bed configuration reduced treatment costs by approximately 57% relative to conventional batch operation and by 39% relative to off-site waste management. These findings demonstrate the technical feasibility and economic competitiveness of nZVI@CS-based recirculating packed-bed systems as a decentralized treatment strategy for Cr(VI)-contaminated laboratory waste liquids.</p>