Recovery of polyphenols onto porous carbons developed from exhausted grape pomace: A sustainable approach for the treatment of wine wastewaters.

Removal of total polyphenols (TPP) is not only necessary as a pretreatment stepfor anaerobic digestion of wine wastewaters (WWW) but also the recovered polyphenols can be used as a dietary supplement. With a view to make the process sustainable, eco-efficient and cost effective, exhausted grape pomace (EGP) after the extraction of polyphenols was impregnated with ZnCl2 (1:1.5) and further activated at 450 °C for 1 h under inert atmosphere. The GPAC (grape pomace activated carbon) thus developed exhibited well-developed porosity with a predominance of micropores, high surface area and selective surface binding sites. Batch adsorption conducted on diluted WWW revealed the better performance of GPAC (84.3% removal) as compared to EGP (48.5% removal) under similar conditions; with maximum adsorption taking place at pH 3.8. While pH studies indicated a possible electron-donor-acceptor mechanism in the binding of TPP, kinetic studies indicated that diffusion was mediated by the porosity in GPAC. Isotherm studies conducted on GPAC and commercial carbon (CAC) revealed multilayer binding under WWW while Langmuir model was operative under simulated conditions. Contrary to the better performance of CAC, the same for GPAC was comparable at higher dosage where >80%TPP was removed from undiluted WWW. The phenol adsorption capacity of GPAC from real (28.4 mg/g) and from simulated wastewater (142.6 mg/g) was higher as compared to other reported adsorbents. Desorption of TPP from loaded GPAC was maximum (∼91%) with 1:1 ethanol-water solvent. The results reveal a sustainable eco-friendly solution for valorisation of exhausted grape pomace for recovery of polyphenols from wine wastewater.