Green Fabrication of Aspergillus terreus–Silver Oxide Bio-Nanocomposite for Sustainable Wastewater Treatments: Synthesis, Optimization, Toxicity Assessment, and Application

The discharge of azo-dye-containing wastewater from textile and related industries represents a major environmental challenge because of the persistence, toxicity, and poor bio-degradability of synthetic dyes. Congo red dye (CR), one of the most widely used azo dyes, poses serious ecological and public health risks when released into aquatic ecosystems. Although numerous biological adsorbents have been investigated for dye removal, the development of sustainable fungal-based nanocomposites with high adsorption efficiency, optimized operational conditions, and verified environmental safety remains limited. Therefore, the present work describes the development and evaluation of a novel Aspergillus terreus–silver oxide nanoparticle (Ag2O NPs) myco-nanocomposite as a promising eco-friendly biosorbent for CR dye removal from aqueous solutions and real wastewater. Aspergillus terreus (GenBank accession PX920301) isolated from dye-contaminated wastewater, the adsorption efficiencies of dried mycelia, and the myco-nanocomposite were compared. Myco-nanocomposite was characterized using ultraviolet visible spectroscopic analysis (UV/Vis), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). A. terreus–Ag2O NPs myco-nanocomposite exhibited the highest ad-sorption efficiency 92.73%, adsorption capacity (qe) 118.7 mg/g and lowest CR dye residual by 3.81 mg/L, while A. terreus non-autoclaved dried mycelia recorded 78.28% CR removal, adsorption capacity (qe) 100.2 mg/g and CR dye residual by 11.39 mg/L. Adsorption parameters were optimized using a four-factor Box–Behnken experimental design, producing a highly significant quadratic model (R2 = 0.986). The highest optimized conditions were obtained at run 17 in which 100 mg L−1 CR dye, pH 8, 0.05 g adsorbent dosage, and 48 h contact time, with removal efficiency of 96.88%, followed by run 14 using 50 mg L−1 CR dye, pH 6, 0.05 g adsorbent dosage, and 48 h contact time, with removal efficiency of 95.79%. Phytotoxicity and microbial toxicity assays demonstrated that the treated wastewater was environmentally safer than untreated CR dye, exhibiting no inhibitory effects on representative bacteria, yeast, and filamentous fungi while improving wheat seedling growth. Furthermore, application of the myco-nanocomposite to real industrial wastewater achieved 94.92% decolorization. This study provides a sustainable myco-nanocomposite of A. terreus–Ag2O NPs which represents a promising green technology for the remediation of dye-contaminated industrial effluents and supports the development of environmentally sustainable wastewater management strategies and applicability of reusing treated wastewater.