World First Biogas Plant to Recover Hydrogen and Methane Quickly from Kitchen Waste
- An Semi-pilot Biogas Plant Based on Two-Stage Fermentation Process -

Energy Technology Research Institute (ETRI) of National Institute of Advanced Industrial Science and Technology (AIST), an independent administrative institute, has established a high efficiency hydrogen/methane fermentation semi-pilot plant to decompose kitchen refuse, paper waste and food waste with anaerobic microbes and to recover hydrogen and methane at the AIST Tsukuba West, in collaboration with Nishihara Environment Technology, Co., Ltd , Ebara Corp., Kajima Corp. and Japan Bioindustry Association. (See Photo.1.)

The R&D work was carried out under a project entrusted by the New Energy and Industrial Technology Development Organization (NEDO), another independent administrative organization,High Efficiency Bioenergy Conversion Project / Development of Highly Efficient Hydrogen-Methane Fermentation Process using Organic Wastes (FY 2001~05)

In the course of R&D works, the effectiveness of the hydrogen / methane fermentation was verified at a laboratory scale with simulated kitchen refuse, paper waste and food waste, and a semi-pilot scale plant will be put into operation at 1/10 to 1/100 of real scale from July.

It has been difficult to dispose high water content kitchen refuse, paper waste and food waste, quickly through the methane fermentation. The R&D work aims at putting the new technology into practical application for decomposing organic waste through anaerobic microbes into hydrogen and carbon dioxide.

The semi-pilot plant, consisting of two-stage processing: solubilization-hydrogen fermentation and methane fermentation, is characterized by reduction of overall processing time from 25days to 15days, upgrading of percent energy recovery from 40~46% to 55%, and high speed and high efficiency decomposition of organic waste to hydrogen and methane, for separate recovery, in comparison to the conventional methane fermentation. (See Photo.2.)

Biomass constitutes renewable organic resource, and its utilization as energy source will serve for environmental clean-up and mitigation of global warm-up. It has been proposed to harness the eco-friendly energy resources at a massive scale. At the Cabinet Meeting in December 2002 it was endorsed to utilize the biomass to the maximal extent in view of reducing greenhouse gas emission and building up recycling-oriented society under the Biomass Nippon Comprehensive Strategy with a specific roadmap for development and introduction.

The methane fermentation has been known as microbe-based technology for producing biogas out of livestock manure and organic sludge, but its application has been limited because of lower decomposition efficiency and slower processing rate. In reality, more than 100million tons of organic waste are, at present, being disposed by incineration and land reclamation without effective recycling.

Under such a circumstance, it has been regarded as serious obstacles for the effective utilization of high water content organic waste, to accelerate decomposition rate of methane fermentation, to upgrade percent energy recovery, to extend processable waste species, and to reduce residual mass.

The two-stage fermentation of hydrogen-methane based on anaerobic microbes is expected not only to solve these problems, but also to contribute to creation of renewable energy, reduced use of fossil fuels, suppression of carbon dioxide emission, lowered burden of waste disposal and creation of new markets.

The construction of the semi-pilot plant is a part of a project Development of Highly Efficient Hydrogen-Methane Fermentation Process using Organic Wastes which was proposed jointly by five expert groups in response to a public offering project High Efficiency Bioenergy Conversion Project (FY 2001-05) and accepted by NEDO for the purpose of developing technology of deriving gas and/or liquid fuel from organic waste.

The semi-pilot plant has been realized on the basis of the development of element technologies since the start of the R&D project, spec decision for tanks of two-stage fermentation and the completion of basic flow for the total system.

The R&D work consists of introducing the solubilization and hydrogen fermentation utilizing the complex microflora established by the recent studies, as a preliminary stage of the methane fermentation, to derive hydrogen and methane from solid organic waste of relatively high water contents. The process of solubilization and hydrogen fermentation increases percent gasification of organic waste and reduces the overall processing time, saving input energy requirements for heating and operation, to improve the percent energy recovery. The final goal of the development is to put the high efficiency hydrogen-methane fermentation plant to practical application in the real scale, aiming at 55% or higher recovery.

It is estimated that the development of the new process reduces the overall process time from 25days to 15days, upgrades the percent decomposition of organic waste from 60-65% to 80%, and improves the overall energy recovery of the system from 40-46% to 55% or more (in term of heat quantity) in comparison to the conventional methane fermentation.

The semi-pilot plant is to verify the effectiveness of the hydrogen-methane two-stage fermentation system through a trial run at 1/10 to 1/100 of real size, using garbage (50kg/day) collected from the cafeteria of the AIST as raw materials, recovering hydrogen fermentation gas 0.5~1m³ per day and methane fermentation gas 5~10m³ per day. (See Table1.)

The R&D work is characterized by separate delivery of hydrogen through the fermentation (See Fig.), and the construction of a semi-pilot scale plant for the hydrogen-methane two-stage fermentation of kitchen garbage is the world first achievement.

Element technologies for the development of the semi-pilot plant carried out by the ETRI-AIST and other collaborative organizations "include Development of anaerobic solubilization process", "Development of hydrogen-methane fermentation process using food waste", "Development of hydrogen-methane fermentation process using recalcitrant organic wastes", "Development on improvement of methane fermentation and its bioengineering",and "Development of cluster hydrothermal process. Through these efforts, essential element technologies such as analysis and control of methane fermentation microflora, solubilization, hydrogen-methane fermentation, have been established.

On the basis of these achievements, the collaboration in joint R&D efforts has been made for the "Development of a Total System" including design, execution, operation and assessment of a semi-pilot plant. The present semi-pilot plant was completed in July 2004, based on the results of element technology R&D

It is expected that the results of the R&D work will contribute to business deployment over a broad area, including the application of hydrogen for fuel cells, and that of methane for gas engines, boilers and fuel cells.