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Biomass energy technology in Japan

Fumitake Tokuyama



The Research Association for Petroleum Alternatives Development (RAPAD) has concentrated its efforts on ethanol derived from cellulose. This paper reviews the research accomplishments of RAPAD, describes efforts elsewhere in methane fermentation and microalgae technology, and discusses the utilization of alternative energy systems in Japan. Conversion technologies and research trends are also reviewed.


Ethanol Production

RAPAD has directed its research toward the production of ethanol from cellulose and concentrated on pretreatment, cellulase enzyme activity, saccharification, and concentration. The primary aim of pretreatment is to break down the cellulose by chemical or physical means to make it more susceptible to enzymatic hydrolysis. RAPAD results have demonstrated that a combination of chemical treatment and explosion can yield high rates of enzymatic conversion. RAPAD has also attempted to screen and develop strong cellulase-producing microorganisms to enhance enzymatic hydrolysis. Mutants of Trichoderma reesei have been selected for further research. In addition, four new cellulase producers, including moulds and bacteria, have also been identified for further research.

To improve enzyme saccharification, RAPAD seeks to produce higher yields of glucose syrup in a shorter time. A continuous saccharification system that uses a low substrate concentration to obtain a high ratio of glucose conversion has been developed.

The research objectives for the fermentation process are to improve the technology for immobilizing yeast cells and to develop an efficient and highly productive fermentation system. RAPAD has developed an alginate-entrapped pilot system to immobilize yeast cells. In operation, the system has worked well. Because of the importance of the fermenter to the efficiency of ethanol conversion, RAPAD has examined fermentation systems and selected a fixedbed, parallel-flow reactor that is used in conjunction with sheets of immobilized yeast cells. RAPAD was able to solve the problems of sludge adhesion to the yeast sheets and of contamination during fermentation.

Methane Fermentation

Japanese research has shown that an immobilized methane-fermentation system improves the efficiency of methane fermentation by reducing the retention time from 16.9 d to 10.8 d and maintaining the same level of gas production. Conventional systems form the acid and gas in one batch, but the immobilized system ferments the methane in two phases (digestion or acid formation, and gasification or methane formation).

Microalgae Technology

Microalgae are capable of direct synthesis of oil. These microalgae are produced commercially for high-value pharmaceuticals and health foods, but there is no technology developed for energy production from these organisms. The Japanese began to develop microalgae technology in 1980. Research has focused on increasing oil yields by species selection and improvement, but this process can be lengthy. Another approach is to increase cell yield by improving the culturing process. The four common technologies for large-scale outdoor production of microalgae are the open bubbling method, the closed circulation method, the open circulation system, and the open sewage-circulation system. Japan is designing its own large-scale outdoor cultivation systems and must choose among an open or closed system, a shallow or deep system, and a synthetic or waste-products medium.

Utilization of Technologies and Systems Analysis

The only significant biomass technology in commercial use in Japan is a program that pellets waste wood to produce briquettes for industrial purposes. The use of ethanol fuel has been studied, and tests have demonstrated that there is no difference between neat ethanol and gasoline.

A comparison of biochemical, thermochemical, and direct combustion technologies reveals that biochemical conversion for ethanol and methane production requires large quantities of raw materials that could be used at a lower cost for electricity generation or for direct combustion. Direct combustion is most feasible because the technology is simple and requires less raw material. Other systems require more research and development to become commercially feasible. The cost of the feedstock and the conversion technology are the major factors that affect the economics of these biomass systems.

Suggestions for Further Research

Areas for further research in Japan include

· The production of liquid fuel from cellulosic biomass,

· The development of systems for local community use,

· The development of systems for international use,

· Cellulosic pretreatment, the establishment of a strong cellulase-producing culture, and the development of an energy-saving process to recover ethanol, and

· The development of a compact pelletizer, a compact gasifier, and gas- or solid-fuel generators to lessen the dependence of agriculture on fossil fuels.