Study on improvement of biohydrogen and biomethane fermentation using hot compressed water treatment

概要

Renewable energy demand is predicted to be increased for next decade. Biomass and biofuel-based energy are estimated to grow 4 and 10 times the current amount at 2030, respectively. Biogas is one of the bioenergy sources that can be produced through the fermentation process. In conventional anaerobic digestion (AD), the biogas from biomass sources produces through some stages: hydrolysis, acidogenesis, acetogenesis and methanogenesis. In recent AD, those stages are separated into 2 physical reactors, which is called two-phase anaerobic digestion (TPAD). In this system hydrogen and methane will be generated in the first and second reactor, respectively. Hydrogen is an ideal energy carrier for the future. Low hydrogen and methane yield is a common problem on anaerobic digestion. Therefore, a certain treatment is needed to improve the yield. In this study, physical treatment using hot compressed water (HCW) is applied to improve the biohydrogen and biomethane production.

To identify the improvement of biogas using HCW treatment, The HCW treatment is applied to inoculum source, biomass as carbon source, and also applied to recirculated-TPAD as a continuous fermentation system. Gas production during fermentation is measured using Gas Chromatography with Thermal Conductivity Detector (GC-TCD) from Shimadzu. The liquid-end products (sugar and organic acid) composition and concentration are measured and calculated using HPLC. Other parameters also recorded using appropriate devices, for instance pH meter, micro-flow meter, etc. The gas production data analysed using modified Gompertz model equation and its derived equation.

The result showed that hydrogen production will increase during several experimental conditions. While using a biomass waste as a natural buffer, hydrogen will reach the highest yield when 1 g/L eggshell powder is used to prevent the pH sharp drop. In other experiment, the application of the HCW condition at 130oC, 0.5MPa for 60 minutes to sake lees (carbon source) and biogas slurry (bacteria source) obtained the highest hydrogen yield, and Clostridium sp and P. agglomerans are interestingly found in this reactor. In a two-phase continuous system (RTAD), HCW treatment at inoculum and substrate resulted in a better reactor performance with higher hydrogen-methane production compared to no-HCW treatment at substrate.

Based on those results, the HCW will improve the biogas production in several ways. First, HCW could improve biohydrogen production by suppressing the methanogens bacteria. Second, HCW will improve biohydrogen production through increasing carbohydrate degradation and increase simple sugar production. Third, HCW will improve the biohydrogen and biomethane production by the combination of suppressing methanogens (that may occur in substrates or effluent of methane reactors) in the inflow of biohydrogen fermentation and hydrolysis of the waste biomass.