New Developments of Methane Fermentation Technology in Japan
Professor Emeritus, Osaka Sangyo University
Methane fermentation is a biological process in which organic materials are converted to methane using anaerobic microbial metabolism centered on methanogenic bacteria under anaerobic conditions. It has long been known that combustible gas (biogas) is produced by anaerobic microbial metabolism in the sludge in lakes and rivers. Greenhouse gas in the atmosphere such as CH4 is likely to increase if this biochemical reaction can not be controlled well.
On the other hand, if biological methane produced in natural ecosystems is technologically utilized, it can lead to technologies for environmental protection, such as anaerobic digestion (sewage sludge treatments), anaerobic treatment (industrial wastewater treatment) and methane fermentation (fermentation field). We will briefly describe the status of methane fermentation in Japan.
Biogas obtained by anaerobic digestion treatment of sewage sludge is generally called digestion gas. There is a report that power generation using digestion gas at a sewage-treatment plant can generate 50% of the energy consumption at the sewage-treatment plant.
Application of anaerobic disposal treatment used for industrial wastewater treatment has been studied since 1950. Since 1960, continuous-stirred tank reactor and anaerobic activated sludge process have been used for purifying alcoholic fermentation wastewater and concentrated wastewater like pulp spent liquor. In particular, since the Upflow Anaerobic Sludge Blanket (UASB) process was developed in Holland in the 1980s, the high efficiency of anaerobic disposal (energy saving, and functions such as control of the extra amount of sludge generation) has been widely acknowledged and over 300 reactors using the UASB process and the EGSB (Expanded Granular Sludge Bed) process were built. They are employed as the standard technology for highly concentrated organic wastewater treatment.
From the beginning of this century, biomass production and utilization for the purpose of sustainable society formation has been promoted and attention has begun to be paid to biofuel. The Japanese government’s target for introduction of liquid biofuels for transportation is set at 4 million kl/yr of crude oil equivalent by FY 2030.
On the other hand, according to Professor Lee’s estimate, if methane gas from methane fermentation treatment of all typical waste biomasses generated in Japan, such as livestock discharges (89 million ton / year), kitchen waste (22 million ton / year) and sewage sludge (75 million ton / year) is recovered, energy from liquid biofuels at 3.95 million kl/yr of crude oil equivalent can be obtained.
Therefore, it's not too much to say that methane fermentation technology is an extremely potent technology as a means of biofuel production. Regarding the biomass production and utilization generated by methane fermentation, the following technologies, such as (1) biogas-fired boilers, (2) electric power generation by gas engine and biogas-fired boilers, (3) fuel utilization for town gas, (4) fuels for natural gas vehicles and (5) high-efficiency power generation by fuel cells are already established
Not only does methane fermentation technology produce biofuels, but it can also meet various challenges such as stabilization and sanitary disposal of waste, production of liquid fertilizer (disposal of livestock discharges) and reduction of the emission of greenhouse gas.
1.Tatsuya NOIKE: The Importance of Methane Fermentation for the Prevention of Global Warming
2.Masao SHIMADA: Present State and New Technologies on Biogas Production of Sewage Sludge
3.Yoshiyasu OKANIWA, et al.: Development of Small Scale Biogas System with Rural Sewage Treatment Plants
4.Takashi KAWANO: Energy Utilization by Hydrogen Methane Fermentation of Shochu Distillation Lees
5.Shinichiro WAKAHARA: Anaerobic Membrane Bioreactors for Food Industry
6.Yoshio OKUNO: Characteristics of Food Wastes Treatment by Water-needless Two-phase Circulated Methane Fermentation System
7.Jun KAWASHIMA: Methane Fermentation of Mixture Biomass in Hita City biomass Recycling Center