Biogas Production from Co-Digestion Vinasse Waste and Tofu-Processing Wastewater and Kinetics

The biogas fermentation co-digestion vinasse waste (VW) and tofu-processing wastewater (TW) was investigated within a wide range of VW:TW of 0:100 - 100:0 (volume ratio). The VW:TW ratio of 0:100, 20:80, 40:60, 60:40, 80:20, 100:0 generated total biogas of 76.11, 159.01, 120.22, 19.96, 18.77, 10.64 mL/g COD respectively. Fitting error between measured and predicted biogas yield by using modified Gompertz model was less (1.18-9.79%) than that by using first order kinetic model (0.82-17.33%). The best variable was VW:TW of 20:80 (COD/N = 1042/7), which had kinetic constant of ym (mL/g COD), mu (mL/g COD/day), lambda (days) of 153.70, 8.49, 1.38 respectively through modified Gompertz equation. The effect of COD concentration on biogas production was successfully described by using Edward model (R-2 = 0.95). Meanwhile, the optimal COD/N obtained from Ratkowsky model was 414/7 (R-2 = 0.96). The developed equation of kinetic model of degradability nitrogen content (KMDNC) was Nt = (Ni/epsilon) - (N/COD)((ci/395) (yt - 395 + ym)).