The preservation of forage crops as silage depends upon the production of sufficient acids to inhibit the activity of undesirable microorganisms under anaerobic conditions. The epiphytic lactic acid bacteria (LAB) that naturally present on forage crops convey sugar into lactic acid in the ensiling process. It is well established that LAB play an important role in silage fermentation. LAB is a major component of the microbial flora which lives in various types of forage crops. The LAB commonly grow with other plant-associated microorganisms during silage fermentation, and they generally define the fermentation characteristics of silage. Moist dairy farm silage is based on natural lactic acid fermentation. The epiphytic LAB transform the water-soluble carbohydrates into organic acids during the ensiling process. As a result, the pH is reduced and the forage is preserved.

However, when the silo is opened and aerobic conditions prevail at feeding time, the silage is subject to aerobic microbial growth and is therefore potentially unstable. Furthermore, the deteriorated silage increases in dry matter loss and reduces in the nutritional value. Generally, the well-preserved silages are considered to be more liable to aerobic deterioration than poorly — fermented silages and some aerobic microorganisms can be harmful to the health of livestock. Therefore, the prevision of aerobic deterioration is an important task in making silage.

New and Renewable Energy Promotion law enacted in 2002 approves bioenergy as a renewable energy and supports its implementation. The total exemption of excise duty is now available for biodiesel used as motor fuel. The current excise duty of diesel is about $0.5/L. All Korean oil refineries should mix a certain amount of biodiesel in their diesel oil products (Table 7.2.2).

7.2.2 Targets

For bioenergy, the following targets have been set up by Korean Ministry of Commerce, Industry and Energy (KMOCIE) in 2002 (Table 7.2.3).

8.1 Small-Scale Biomethanation

8.1.1. What are biomethane and biomethanation?

Biomethane (sometimes referred to as "Biogas) is generated from organic materials as they decay. The main component of biomethane is CH4 (55%-70%) and CO2 (25%-40%). Biomethane can be used for cooking, lighting, heating, generating electricity and so on.

Biomethanation is the process of conversion of organic matter in the waste (liquid or solid) to biomethane and manure by microbial action in the absence of air, known as "anaerobic digestion."

8.1.2. Situation of biomethane in China

The annual quantity of waste in China is more than 150 million tons. The production and disposal of large quantities of life and industrial waste without adequate or proper treatment result in widespread environmental pollution. While some of these wastes can be collected and biomethane is generated from anaerobic digesters where the manure decomposes. Especially in some far rural area where the transportation of electricity is expensive, biomethane is a good way to provide energy for cooking, lighting and heating, etc.

Since 1950s, Chinese governments encouraged small-scale biomethanation using animal and agricultural waste as feedstock. Table 1 shows the rural biomethane development in China. Till 2006, about 20 million families in rural area are using biomethane for cooking and lighting. Annual consumption reaches 5 million standard coal equivalent. Subsidy of 2.5 billion RMB from government is for small-scale biomethanation development, which means one small-scale biomethanation can get subsidy of 800-1200 RMB. China nation government plans to build 30 million biomethane digesters in 2010 and 45 million biomethane digesters in 2020.

The economies of all countries, and particularly of the developed countries, are dependent on secure supplies of energy. Energy security means consistent availability of sufficient energy in various forms at affordable prices. These conditions must prevail over the long-term if energy is to contribute to sustainable development. Attention to energy security is critical because of the uneven distribution of the fossil fuel resources on which most countries currently rely. The energy supply could become more vulnerable over the near term due to the growing global reliance on imported oil. Biomass is a domestic resource which is not subject to world price fluctuations or the supply uncertainties as of imported fuels.

Productivity of E. crassipes was recorded as 11-23 kgFW (fresh weight)/m2.year (0.5-1.2 kgDW (dry weight)/m2.year) during growing season in Japan, and reached 21.1 kgDW /m2.year under sufficient light and nutrients. Eel grass productivity is 0.3-0.8 kgDW/m2.year (120-320 gC/m2.year), and that of Thalassia reached 5 gDW/m2.day during 8 months in Florida, U. S.A.

Red alga, Hypnea, had productivity of 12-17gDW/m2.day in outdoor tank (Slesser and Lewis, 1973). Productivity of micro-algae is 2-10 gDW/m2.day in outdoor tank on average, and increases to 500 gDW/m2.day under the optimum condition.

In China, the effects of CCB use for an economy and an environment are estimated as follows; As for the consumption of coal decrease 20%, because CCB includes a biomass of 20%. And, by improvement of flammability of fuel, about 25% heat efficiency becomes higher than a present coal boiler. When CCB were consumed 1,000,000 t/year in China, it is estimated that

400,0 t/year of coal consumption, 5,000 t/year of smoke emission and 15,000 t/year of sulfur dioxide are decreased.

Further Information

Johanson, J. R. ;The Use of Laboratory Tests In The Design and Operation of Briquetting Presses, Proceedings, IBA, 13, 135(1975)

Maruyama, Coal-wood formed fuel Binder effect of woody materials, Hokkaido Industrial Research Institute, No.279, 183(1980)

Maruyama, Briquetting characteristics of coal-wood composite fuel, Report of Hokkaido Industrial Research Institute, No.282,195(1984)

Groring, D. A. I.;Thermal Softening of Lignin, Hemicellulose and Ceullulose, Pulp Paper Mag., T-517~ 527(1963)

The Japan Institute of Energy, Biomass Handbook, p224-228(2002)

When organic compounds are maintained at 5-70°C and neutral pH under anaerobic conditions, spontaneously biomethanation will happen. Biogas is often produced from underground of landfill. Kitchen garbage and sewage sludge have been used as substrates of biomethanation. Organic wastewater from food factory containing sugars and starch has been also used as substrate for biomethanation.

Biomethanation is composed of hydrolysis, acetogenesis and methanogenesis. Fig. 5.1.1

indicates an outline of biomethanation. Polysaccharides are decomposed to monosugars, proteins are to amino acids, and fats are to fatty acids and glycerol. Fermentative bacteria are for example Bacteroides spp. and Clostridium spp. Sugars and amino acids are decomposed to acetate and propionate by acidogens. Finally, methanogens convert acetate or hydrogen and carbon dioxide to methane. Acidogenesis is a complex process in which microflora of anaerobes collaboratively decomposes organic compounds to low molecular organic acids. Acetate, lactate, succinate, ethanol, butanol, acetone and etc. can be produced from glucose by acidogens. In wastewater treatment, 70% of methane is produced from acetate, and 30% is produced from hydrogen and carbon dioxide. Formula of acetoclasic reaction is as follows;

CH3COOH—CH4+CO2

Formula of hydrogenotrophic reaction is as follows;

CO2+4H2——CH4+2H2O

Methanogens are anaerobes which can grow using acetate or hydrogen and can produce methane. Representative methanogens are Methanobacter spp. and Methanosaeta spp.

Methanogens are killed by exposure to oxygen; therefore, methane formation requires obligate anaerobic conditions. Phylogenetic analyses indicate that methanogens are placed in Archaea group, distinguished from eukaryote and prokaryote. Methanogens can only use hydrogen, formate, acetate, 2-propanol, 2-buthanol, methylamine, methanol, methylmercaptan to produce methane.

For biomass utilization, pretreatment such as transportation from plantation site, crushing (tipping), and drying are required.

Although each conversion technology requires particular chip size and moisture content of biomass, Table 6.2.5 shows an example (transportation energy, crushing energy, and drying energy). To calculate the transportation energy, it was assumed that 5 t-dry biomass was transported by the track whose maximum load is 20 t and fuel mileage is 3 km/L. The crushing energy was obtained from the reference. Drying energy was calculated, assuming that biomass is dried till water content becomes 20% from 50%, considering approximately 20% heat loss in addition to the evaporation heat.

When transportation distance is 30 km, preprocessing energy is 75 MJ/t-dry (3.6%) for transportation, 0.786 MJ/t-dry (0.037%) for milling and 2,032 MJ/t-dry (96.4%) for drying respectively. This shows that energy consumption in transportation stage is relatively small on this assumption. Energy consumption in drying stage would be reduced by natural drying or drying with waste heat.

□ 94 % of fuel wood is used directly as fuel,

□ 6 % of fuel wood is converted to charcoal,

□ 90 % of total fuel wood supply is consumed directly by households in rural areas,

□ 8 % of total fuel wood supply is used in other urban households,

□ Less than 1 % of total fuel wood supply is used in industrial sector,

□ Less than 1 % of total fuel wood supply is used in service sector

□ The other biomasses such as wood, wood waste and rice husk are used by brick kilns, bakeries, and food processing,

□ Cane husk, palm branches and tree leaf are used by cane sugar and palm sugar producers,

□ Coconut branches, coconut husk and rice husk are used by rural households for cooking animal food,

□ Some rural households use coconut branches, palm branches, rice straw with cow dung, rice husk and wood waste for cooking their food.

□ They use these biomasses for directly firing.

8.5.1 What is a good source for ethanol production?

In Thailand, most existing commercial ethanol production plants use molasses as a feedstock but with increasing new facilities to use cassava in the near future. However, these two energy crops are still considered as food, which may interfere with the ‘food vs. fuel’ issue. As a result, more people are looking for alternative non-edible energy crops. Among many others, lignocellulose from various agricultural residues has received a great deal of attention, commencing the era of 2nd generation lignocellulosic bioethanol.

8.5.2 Lignocellulosic biomass feedstock for ethanol in Thailand

Each year in Thailand, agricultural industries generate millions of tons of various lignocellulosic biomass feedstock known as agricultural residues, including rice straw, sugar
cane bagasse, corn stover/fiber and wood chip. Sugarcane and rice, mostly concentrated in the North and Northeastern provinces, are the first two largest national agricultural productions (in weight) as shown in the table below.

Table 8.5.1. The first four largest agricultural production in Thailand (2004).

In general, these residues are inefficiently utilized, which most often, also causes environmental problems. Rice straw is considered wastes and disposed off through various methods such as open-air burning (as shown in Fig. 8.5.1 and 8.5.2), dumping or animal feeding. A rather more attractive method to mange these abundantly available rice straws is through cellulosic ethanol