Anaerobic Gasification of Liquefied Okara

Abstract

It is necessary to utilize Okara which is a byproduct of soybean processing. For this purpose, an anaerobic methane fermentation system is proposed to transform Okara to biogas which is used as recycling energy. In this experiment, a bench scale anaerobic contact process which is composed of CSTR's was experimentally used to treat the supernatant of liquefied Okara from the liquefaction reactors in the steady state. Four experimental runs with COD loading rates from 1980 to 3440mg/L/d were conducted at 30 days of HRT. It was found that the gasification process worked and showed the VS removal ratio from 72 to 80% as long as its pH was controlled within the range of neutrality. Obtained v_max and K_s as apparent kinetic parameters based on the material balance and the growth model for the process were 0.55mg-COD/mg-VSS/d and 5400mg-COD/L respectively. They indicated that the phase separation of methane fermentation activated the microbial growth and the reactors required the improvement in the mixing method. The simulation based on the energy yields in this experiment revealed that the feasibility of the anaerobic methane fermentation system to produce the recycling energy from Okara would be best improved by increasing the VA yield for the liquefaction rather than trying to improve the methane yield for the gasification.