Produção de metano a partir da codigestão do caldo do capim elefante e vinhaça

Abstract

The production of energy by fossil sources can lead to great damages to environment. One way to reduce these damages is to use biomass as an energy source, such as elephant grass broth (EGB) and vinasse. However, the use of these biomasses together in the production of methane still has challenges to be overcome. One of these obstacles is the abrupt reduction of pH by EGB. Thus, the present study aimed to evaluate the potential for methane production through anaerobic co-digestion of EGB and vinasse in a batch reactor using sludge from a UASB reactor (Upflow Anaerobic Sludge Blanket) as inoculum from an STP. The experiments to study this system were performed according to the Box-Behnken statistical design of experiment and Response Surface Methodology. This design consists of three factors: addition of sodium bicarbonate; the proportion of substrates mix and inoculum concentration. Three levels of each factor were chosen: 0.05, 0.15 and 0.25 gHCO3:gCOD, for addition of sodium bicarbonate; 25:75, 50:50 and 75:25, for the proportion of EGB and Vinasse (EGB/V); and 10, 15 and 20% of inoculum concentration, in reference to the reaction volume. Through Box-Behnken planning, it was possible to provide a response surface to evaluate the interaction between the factors and the production of methane (CH4). The reactors were operated for 33 days, which resulted in an accumulated production of CH4 varying between 372 and 1092 mLCH4/gSV. The experimental design provided a quadratic regression equation with R2 of 0.9213. Through the model was possible to obtain the optimal points of each factor for the production of accumulated CH4, being 0.19 gHCO3:gCOD, 50.78:49.22 (EGB/V) and 15.60% for bicarbonate, mixing ratio and inoculum rate respectively, these optimal points resemble one of the reactors that most produced accumulated CH4. The highest production of accumulated CH4 had bicarbonate addition close to optimal point, so it can be understood that bicarbonate is a limiting factor in increasing the production of accumulated CH4.