Sustainable conversion of cassava bioethanol residues into activated carbon for COD and color removal from industrial wastewater and energy recovery

Abstract

This study presents a sustainable strategy for valorizing cassava-based bioethanol residues—peels, pulp, and wood ash—into activated carbon for industrial wastewater treatment. The activated carbon was produced via chemical activation with KOH, optimizing key parameters including biomass composition, impregnation ratio, and activation temperature. The optimal condition (1:4 impregnation ratio at 700 °C) yielded a porous carbon material with enhanced surface characteristics. Adsorption experiments using real bioethanol wastewater demonstrated efficient removal of chemical oxygen demand (COD) and color under optimal operational conditions (pH 5, 60 min contact time, and 80 g/L dosage), reducing COD to 46.08 mg/L and color to 198.8 ADMI—both within Thailand’s industrial discharge standards. The adsorption process followed the Freundlich isotherm model, indicating multilayer adsorption on a heterogeneous surface. In addition to pollutant removal, the spent activated carbon retained significant calorific value (1601.23 kCal/kg), enabling its reuse as a low-grade fuel in industrial boilers. This dual-function approach not only mitigates environmental impacts from agro-industrial waste but also supports circular economy principles through resource recovery and energy reuse. The proposed method offers a cost-effective and scalable alternative for wastewater treatment in the bioethanol industry and has broader implications for sustainable waste management in related sectors.