Mitigation of sulfate contamination from brine using bioadsorbent derived from fermented date fruit pomace: preparation, characterization, and adsorption performance

Abstract

Appropriate management of fermentation residues which comprise valuable components, such as nutrients, organic compounds, and energy-rich molecules minimizes the reliance on new raw materials and promotes circular economy principles. In this study, fermented date fruit pomace, a solid residue after the lactic acid fermentation of date fruit pomace is converted to a bioadsorbent for sulfate removal from high-salinity rejected brine, which is a major challenge for desalination plants; the high sulfate content in brine creates environmental issues. Brine with high sulfate content accelerates the corrosion of pipelines, equipment, and metal structures, resulting in increased maintenance costs, safety risks, and potential leaks. The proposed process converts the fermented date fruit pomace to activated carbon using sodium hydroxide. Sulfate removal of 90.9% was achieved when 500 mg/L brine was treated with 20 g/L of activated carbon at 25 °C for 2 h with a BET surface area of 166.48 m2/g. The mechanism of the sulfate adsorption fits the Langmuir model (monolayer adsorption) with a maximum adsorption capacity of 415.2 mg/g. The adsorption isotherms and kinetic model indicate that the adsorption is exothermic in nature and follows a monolayer adsorption process in close alignment with both pseudo-first- and pseudo-second-order kinetics, indicating that sulfate adsorption is both physical and chemical in nature. Boyd’s plots indicate that sulfate adsorption is controlled by film diffusion or a chemical reaction. Post-adsorption analysis by XRD, SEM-EDS, and FTIR indicates that the bioadsorbent surface of the activated carbon was loaded with sulfate. This study demonstrates the value of converting date fruit pomace to a bioadsorbent.

Keywords: Activated carbon, Adsorption, Fermentation residue, Isotherms, Kinetic model, Langmuir