Exploring the Synergistic Effects of Mixing, Initial pH Variability, and Light Wavelength on Diatom-Mediated Wastewater Remediation

Though diatoms as agents to remove silica pollutants have already been tested, the factors governing the photobiological process remain unexplored. The current process was developed to optimize various combinations of abiotic factors like pH (5, 6, 7, 8, and 9), mixing conditions (aeration, magnetic stirrer, and shaking-induced mixing), and light wavelength (red: 665–630 nm, blue: 465–430 nm, and white: 665–420 nm) for silica removal using diatom Navicula sp. from WC media. A combination of pH 7 and magnetic stirrer mixing (80–100 rpm) gave the best silica removal at 11.93 ± 0.15 mg L–1d–1. This optimized process with blue wavelength light increased the silica removal rate to 14.43 ± 0.37 mg L–1d–1 and biomass productivity to 95.15 ± 1.34 mg L–1d–1. Further, bioremediation of cooling tower blowdown water was tested under optimized and unoptimized conditions. A silica removal rate of 13.90 ± 0.26 mg L–1d–1 was achieved under optimized conditions, 3.69-fold greater than the unoptimized conditions (3.77 ± 0.42 mg L–1d–1). Additionally, this process removed >99% of total dissolved phosphate (3.05 ± 0.10 mg L–1d–1), nitrate nitrogen (12.27 ± 0.49 mg L–1d–1), and 54.27% chemical oxygen demand. Such optimization of abiotic factors using diatoms helps in achieving green silica-rich wastewater bioremediation.