Eco-friendly Nanocomposites for the Degradation of Emerging Contaminants in Wastewater Systems

Abstract

Emerging contaminants (ECs) including pharmaceuticals, endocrine-disrupting compounds (EDCs), microplastics, and personal care products have become persistent pollutants in aquatic environments due to their resistance to conventional wastewater treatment methods. This study investigates the green synthesis, comprehensive characterization, and exceptional performance of biodegradable, plant-based nanocomposites for the removal and degradation of ECs from wastewater systems. Eco-friendly nanomaterials were synthesized using cellulose nanocrystals, chitosan, and starch matrices embedded with metal oxide nanoparticles (ZnO, TiO₂, CuO, Fe₃O₄), functionalized through phytochemical reduction using extracts from Camellia sinensis (green tea), Moringa oleifera, Aloe vera, and Azadirachtaindica (neem). The biosynthesized nanocomposites demonstrated optimal physicochemical properties with high surface areas (50–300 m²/g), nano-scale particle sizes (10–100 nm), and zeta potentials of ±30-50 mV ensuring colloidal stability. Remarkable removal efficiencies of 87.3–96.5% were achieved for diverse contaminants: Fe₃O₄/chitosan-green tea (94.2% tetracycline), ZnO/cellulose-moringa (89.7% BPA), TiO₂/alginate-aloe vera (91.5% microplastics), and CuO/starch-neem (87.3% ibuprofen), representing 3-15 fold improvements over conventional methods. Mechanistic studies revealed synergistic tri-modal action through physical adsorption via π-π interactions and hydrogen bonding, photocatalytic degradation generating reactive oxygen species (•OH, O₂•⁻), and enzymatic breakdown through laccase-mediated oxidation. Kinetic analysis confirmed pseudo-second-order behavior (R² > 0.99) with rate constants 2-5 times higher than conventional adsorbents, while thermodynamic parameters revealed spontaneous, exothermic processes (ΔG° = -22.8 to -30.2 kJ/mol). Exceptional reusability was demonstrated over 12-18 cycles with >85% efficiency retention. Comprehensive biodegradation studies under OECD 301F conditions showed >78% mass loss within 45 days, with microbial community analysis (16S rRNA sequencing) identifying specific degradative organisms (Bacillus subtilis, Trichoderma viride, Pseudomonas putida) and enzymatic activities (cellulase: 47.2 U/g, chitinase: 52.8 U/g, amylase: 38.9 U/g). Temperature-dependent kinetics revealed activation energies of 47.3-52.3 kJ/mol and Q₁₀ coefficients of 2.0-2.3, confirming biological degradation mechanisms. Extensive safety assessment showed metal leaching far below regulatory limits (Zn <0.05 μg/L, Cu 0.18 μg/L, Fe 0.45 μg/L), low bioaccumulation factors (BCF: 8-47, BAF: 0.18-0.89), and minimal ecotoxicity (LC₅₀>400-1000 mg/L for Daphnia magna and Lactuca sativa). Life cycle assessment using SimaPro 9.5 revealed dramatic environmental benefits: 68-85% reductions in greenhouse gas emissions, fossil fuel consumption, and human health risks compared to conventional nanomaterials, with negative carbon footprints (-12.8 to -18.5 kg CO₂-eq/kg) through composting scenarios. Material recovery rates of 78-90% contributed to exceptional circularity indices (0.89-0.95). This study establishes plant-derived nanocomposites as transformative, environmentally compatible solutions for mitigating emerging pollutants, offering unprecedented combination of high efficiency, biodegradability, safety, and sustainability for both centralized and decentralized water treatment applications.