Cultivating conditions optimization of the anaerobic digestion of corn ethanol distillery residuals using response surface methodology

This study investigated the individual and interactive effects of three factors — temperature, inoculum/substrate ratio (ISR) and inoculum typology — on the anaerobic digestion of corn ethanol distillery wastewater. Biochemical methane potential assays planned with factorial design with two independent quantitative variables on three levels (ISR: 1:1, 2:1 and 3:1; temperature: 30°C, 33.5°C, 37°C) and one independent qualitative variable (inoculum type: suspended, granular, mixed) have been performed. Response Surface Methodology has been used to study the effect of the factors with the aim of maximizing the specific methane yields (Y CH4 ) obtainable with this substrate. The results show that all three investigated factors influence in a significant matter the Y CH4 , the ISR having the strongest effect on it. The temperature has significant influence on the Y CH4 only in combination with high ISR values. The optimal conditions for the maximum Y CH4 (551 mL CH 4 g −1 VS added ) have been found at 37°C operating temperature, ISR=3:1 and using granular inoculum. These conditions gave rise to a 4-fold increase of Y CH4 with respect to the worst combination of factors (Y CH4 =129 mL g −1 VS added for the suspended inoculum type, at 30°C and ISR=1:1). The results improve the knowledge on the digestion of this substrate, providing information for successful process up-scaling.