Optimizing Biogenic Silica Recovery from Diatoms: A Life Cycle Analysis of Surfactant and Bleach Treatments

Abstract

The conventional acid and thermal treatments used for frustule recovery from diatom biomass are hazardous and unsustainable and may distort frustule structure. This is the first study to employ diatoms cultivated in domestic reverse osmosis reject wastewater for mesoporous biogenic silica production by investigating sustainable extraction routes using various surfactant types and bleach treatments at different concentrations. The highest organic matter removal of 81.68 ± 0.58% (w/w) was attained with a 4% (v/v) bleach treatment, while an 8% (v/v) anionic surfactant treatment yielded an organic matter removal of 81.62 ± 0.36% (w/w). The results have been confirmed through Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis, field emission scanning electron microscopy, energy-dispersive spectroscopy, carbon–hydrogen–nitrogen analysis, and Brunauer–Emmett–Teller analysis. FTIR peaks at 1109 cm^–1, 1101 cm^–1, and 3437 cm^–1 indicated silica in the extracted frustule. The bleach-treated frustules had mesoporous structure, exhibiting −17.6 ± 0.9 mV, 19 m² g^–1, and 31.99 ± 0.5 nm of surface charge, surface area, and average pore diameter, respectively. Life cycle assessment indicated that the bleach-cleaning process reduced the environmental impact by 99% compared to conventional acid treatment. Hence, this study presents a sustainable approach for extracting biogenic silica from diatoms, offering a greener alternative to conventional methods and reducing reliance on synthetic mesoporous silica.