para‑Nitrophenol nano‑biodegradation using Turbinaria triquetra‑synthesized magnetic nanoparticles‑coated novel bacteria: a sustainable approach for refnery wastewater treatment

Abstract

Recently, nano-biodegradation is considered promising for environmental reclamation. In this study, selective enrichment technique was applied for isolating a novel bacterium, Bacillus nealsonii strain HN9 (NCBI Gene Bank Accession No. MZ081627) capable of degrading high concentrations of para-nitrophenol (pNP) via the hydroquinone pathway. Sustainable Turbinaria triquetra hot aqueous extract (TAE) was successfully used as a revolutionary reducing, stabilizing, and capping agent in a one-pot mild operating process for the green synthesis of ecofriendly, crystalline, non-toxic, polydispersed, multishaped, highly stable Fe3O4 NPs with average size, specifc surface area, and magnetic saturation of 26.31 nm, 82.48 m2 /g, and 57.57 emu/g, respectively. In a cutting-edge approach, response surface methodology and artifcial neural network were applied for modeling and optimizing the pNP nano-biodegradation batch process using the TAE-synthesized MNPs-coated HN9. Approximately complete removal of pNP was achieved at the predicted optimum operating conditions of 12,900 mg/L salinity, 30 °C, pH7, 0.38 g/g MNPs to biomass ratio (M/B), 170 RPM, and 400 mg/L pNP concentrations within 48 h. Relative to free cells, the MNPs-coated cells expressed a fve-times higher pNP biodegradation rate, higher storage and operational stability, and could be used for fve successive times without losing its activity, besides the advantage of magnetic separation. Upon the pioneering application of TAE-synthesized MNPs-coated HN9 for the nanobioremediation of refnery wastewater, the removal rate of BOD, COD, TPH, PAHs, and phenols recorded 12.15 mg/L/h, 12.10 mg/L/h, 1.68 mg/L/h, 4.27 mg/L/h, and 8.84 mg/L/h, respectively. That was approximately three-times higher than that recorded in batch bioreactor inoculated by free HN9.