Enhancing vinasse biodegradability through ozonation: a response surface approach toward biogas-oriented wastewater valorization.

Vinasse, a byproduct of the ethanol industry, poses significant challenges for anaerobic digestion due to its high concentration of recalcitrant phenolic compounds and its tendency to generate excessive foam, which destabilizes reactor hydrodynamics. This study introduces a methodologically transparent approach to pretreating vinasse for anaerobic digestion. While ozonation and polydimethylsiloxane (PDMS) antifoam are established individually, their combined application for processing highly recalcitrant agro-industrial wastewater requires precise control. PDMS was introduced as an operational prerequisite to suppress severe foaming and physically prevent reactor overflow. With physical stability maintained, Response Surface Methodology (RSM) via a central composite design (CCD) was employed to mathematically optimize the critical chemical process variables-pH, ozone flow rate, and contact time-to detoxify the substrate without inhibiting downstream microbial activity The results indicated that ozonation significantly enhanced biodegradability, with the optimal conditions determined at pH 4.0, an ozone flow rate of 2.0 L/min, and a contact time of 90 min. Under these conditions, the treatment achieved high removal efficiencies for COD and phenolic compounds while reducing the carbon-to-nitrogen (C/N) ratio to 16.7, thereby altering the substrate balance before final nutrient adjustment for methanogenesis. Validation experiments confirmed that the operationally stabilized ozonation process increased the methane yield to 0.22 L CH4/g COD, a 37.5% increase over untreated vinasse (0.16 L CH4/g COD). These findings demonstrate that integrating PDMS with ozonation shows strong lab-scale potential to overcome the mechanical and chemical barriers inherent in processing high-strength agro-industrial wastewater, warranting further pilot-scale engineering studies.