Adsorption-supported ozonation of complex mariculture wastewater pharmaceuticals using a greener (Ni/Fe–C) nano-composite derived by co-pyrolysis of coconut shell and partially reduced iron: mechanism and implications

Abstract

Undeniably, intensive utilization of emerging antibiotics like oxytetracycline (OTC) and other complex pharmaceuticals in mariculture poses an ecological threat. Similarly, hazardous wastes like partially reduced iron ore (RI) and coconut shell residue (CNR) can potentially leach heavy metals and release greenhouse gases. Herein, a waste-based, inexpensive, and eco-friendly one-pot co-pyrolysis of RI and CNR (1 : 5) and Ni-wet impregnation (2.5%, 5%) at temperatures of 300 °C, 500 °C, and 700 °C under an N₂ atmosphere achieved synergistic Ni/Fe–C integration. Characterization of the bimetallic Ni/Fe–C nano-composite confirmed enhanced CO, C–O–C, and Fe/Ni oxide groups. Firstly, the adsorption-combined catalytic lean ozonation degradation-based strategy successfully enhanced the degradation of pharmaceuticals in real mariculture wastewater. 2.5% Ni/Fe–C at 700 °C exhibits optimum performance with minimal ozone usage and also recovers nutrients (P, K, and Ca). ICP-MS and toxicity tests showed 0.1 g as the safest dosage. High-performance liquid chromatography (HPLC) and triple quadrupole liquid chromatography-mass spectrometry (QTRAP ABI-3200) detected more than 28 pharmaceuticals, with enhanced removal (<0.01 ppm). 2.5%Ni/Fe–C-700 °C exhibited robust stability, reusability, and magnetization. Density functional theory (DFT) calculations and electron paramagnetic resonance (EPR) confirmed exceptional electron transfer and active sites for ozone depletion, while enhanced in situ singlet oxygen (¹O₂) generation was seen within hydroxyl (˙OH) and superoxide (O₂˙⁻) radicals. Life cycle assessment (LCA) and liquid chromatography-mass spectrometry (LC-MS) explored the greener degradation process, and the successful growth of Chinese cabbage, Escherichia coli, and zebrafish was seen in treated wastewater. These novel insights suggest efficient industrial waste utilization by adopting a cutting-edge, sustainable way of waste upcycling.