Solophenyl Red 7BE Dye Biosorption Using Raw Sunflower Seed Hulls: Ionic Strength, Regeneration, and Real Textile Effluent Application.

Abstract

Despites its widespread use in the textile industry, Solophenyl Red 7BE dye remains poorly studied. This study investigates the removal of the anionic dye, Solophenyl Red 7BE (Direct Red 227), from aqueous solutions and subsequently validates the process using a real textile effluent. The low-cost lignocellulosic agro-industrial by-product, raw sunflower seed hulls, was used as biosorbent. Batch experiments achieved over 97% removal at neutral pH (7-7.5), 24°C ± 3°C temperature, 20 mg L^-1 dye concentration, 2.5 g L^-1 biosorbent, and 90 min contact time. The regeneration and reusability of the biosorbent were also evaluated using NaOH to assess its potential for repeated adsorption cycles. Results show that the removal is efficient until the third cycle. It is also found that NaOH is the suitable eluent for the desorption of anionic dyes. The adsorption process followed the pseudo-first-order kinetic model and was well described by the Temkin isotherm. Analysis techniques such as FTIR, XRD, XPS, BET, SEM-EDS, and thermogravimetric analysis (TGA) confirm the involvement of surface functional groups. Dye removal experiments from real textile effluent showed that adsorption increased from 17.6% to 84.6% after NaCl addition. This demonstrates that the controlled ionic strength is an effective operational strategy for enhancing the adsorption of Solophenyl Red 7BE under realistic wastewater conditions. These findings provide a practical basis for the sustainable treatment of saline textile wastewaters containing poorly investigated dyes and encourage further evaluation of low-cost biosorbents under realistic industrial conditions.