Innovative Use of Spent Brewer's Yeast for Tannin Adsorption from Treatment Solution

This study aimed to evaluate the capacity of spent brewer's yeast (BSY) to adsorb tannins and other phenolic compounds from an alkaline-extracted chestnut shell tannin solution (CS tannin extract). The alkaline extraction process used 5% NaOH (v/v), a method commonly employed to extract cellulosic material from chestnut shells (CSs). The findings of this research contribute to the development of more sustainable laboratory practices and enhance the economic viability of cellulosic material extraction from CS.

Various treatments—lyophilization, immobilization in calcium alginate beads, and both alkaline and acid treatments—were applied to BSY to determine which method resulted in the highest tannin adsorption capacity from the CS tannin extract. Kinetic and equilibrium adsorption studies were performed to identify the best adsorption approach. The tannin content was analyzed using the Folin–Ciocalteau method, with results expressed as milligrams of tannic acid equivalents (TAEs) per milliliter of extract solution. The adsorbent material was characterized before and after the experiments; the characterization methods included the determination of the point of zero charge (pH_PZC), Fourier Transform Infrared (FT-IR) Spectroscopy, and Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM/EDS).

Equilibrium was reached within 10 minutes, with the highest (p<0.05) biosorption capacity of tannins from the CS tannin extract observed in lyophilized BSY (35.51 ± 0.97 mg TAE per gram of BSY). The Sips models provided an adequate description of the adsorption process, indicating that tannin biosorption by BSY is driven by chemisorption. FTIR analysis identified various functional groups in BSY, with carboxyl, amino/hydroxyl, and amide groups playing a significant role in the biosorption process.

Overall, these findings suggest that BSY has potential as a delivery system for the valorization of tannins from treatment solutions.