Kinetic Model of Biogas Yield Production from Vinasse at Various Initial pH: Comparison between Modified Gompertz Model and First Order Kinetic Model

Abstract

Anaerobic treatment using anaerobic digestion can convert organic materials of vinasse into biogas. The purpose of this study was modeling kinetic of biogas production using modified Gompertz model and first order kinetic model at variation of initial pH. Substrates were consisted of two kinds of compositions, which were vinasse+rumen (VR) and vinasse+rumen+urea (VRU). Initial pH in each substrate was 6, 7 and 8. Degradation process was done in 30 days using batch anaerobic digesters at room temperature. Both, at VR and VRU, initial pH of 7 generated the more total biogas than the others two (initial pH of 6 and 8). Biogas formed at substrate of VRU was more than that at substrate of VR. The best condition was substrate of VRU and initial pH of 7. At best condition, kinetic constants of biogas production model using modified Gompertz were ym (biogas production potential) = 6.49 mL/g VS; U (maximum biogas production rate) = 1.24 mL/g VS. day; &lambda (minimum time to produce biogas) = 1.79 days. Whereas kinetic constants of biogas production model using first order kinetic were ym (biogas production potential) = 6.78 mL/g VS; k (biogas production rate) = 0.176 /day. The difference between the predicted and measured biogas yield (fitting error) was higher with the first-order kinetic model (1.54-7.50%) than with the modified Gompertz model (0.76-3.14%).