The current study aims to examine the concentration of some toxic elements such as, cadmium (Cd), chromium (Cr), lead (Pb) and nickel (Ni) and physicochemical parameters such as electric conductivity (EC), pH, total dissolved solids (TDS), and biological oxygen demand (BOD) in the wastewater of dye manufacturing, textile dyeing, and small dyeing industries. The concentrations of Cd, Cr, and Ni in wastewater samples of these industries were significantly higher than the permissible limits set by WHO for toxic metals in industrial wastewater. The highest level of EC was observed in wastewater samples of the small dying industry as compared to the other two types of industries. The BOD of the investigated wastewater samples was almost two to three-times exceeded than the suggested threshold level recommended by EPA for industrial wastewater. The elevated BOD levels might be due to the presence of the excess level of organic matter in wastewater discharged from the various activities of industries.

Titanium dioxide nanoparticles (TiO₂-NPs) were synthesized using the molten salt method and systematically characterized. TiO₂-NPs were evaluated for their capacity to promote the growth of Capsicum annuum cultivars together with the plant growth-promoting microorganisms (PGPMs) Bacillus thuringiensis (Bt) and Trichoderma harzianum (Th). The variables analyzed included physiological parameters and antioxidant responses. The capacity of TiO₂-NPs to scavenge free radicals was also investigated, along with their biocompatibility, using Artemia salina as an in vivo model. The results demonstrated that TiO₂-NPs exhibited a nanocuboid-type morphology, negative surface charge, and small surface area. It was noted that TiO₂-NPs enhanced the CFU and spore production of Bt (1.56–2.92 × 10⁸ CFU/mL) and Th (2.50–3.90 × 10⁸ spores/mL), respectively. It was observed that TiO₂-NPs could scavenge DPPH, ABTS, and H₂O₂ radicals (IC₅₀ 48.66–109.94 μg/mL), while not compromising the viability of A. salina at 50–300 μg/mL. TiO₂-NPs were determined to enhance the root length and fresh and dry weights of chili peppers. Similarly, TiO₂-NPs in synergy with Bt and Th increased the activity of β-1,3-Glucanase (2.45 nkat/g FW) and peroxidase (69.90 UA/g FW) enzyme activity, and increased the TPC (29.50 GA/g FW). The synergy of TiO₂-NPs with the PGPMs consortium also upregulated the total chlorophyll content: 210.8 ± 11.4 mg/mg FW. The evidence from this study unveils the beneficial application of TiO₂-NPs with Bt and Th as an efficient approach to promote the physiology and antioxidant responses of chili peppers.