Refer to Sec. 1.14, Chap. 1, for more details on biomass. Solid products fall under the following categories:

1. Direct outcome of photosynthesis: Products from forest, shrubs, agri­cultures, and aquacultures.

2. Nonphotosynthesis: Mushrooms, animal biomass, indirect from photofixation.

3. Wastes: Forests and agricultural products.

4. Municipal solid wastes: Not all solid biomass may be suitable for dif­ferent end uses, i. e., energy production or energy recovery. For exam­ple, mushrooms are notably useful as food, feed, or fodder, not otherwise. Biomass properties are guidelines to further and more fruitful end uses. The properties depend on the following:

a. Water or moisture content (aqueous/dry)

b. Calorific or combustion value

c. Dry residues/ash content/silicates, and so forth

d. Alkali metal/oxides in the ash

e. Ratio of cellulose/liquid/oils/fats/of other carbonaceous matters

f. Ratio of solid/liquid/volatiles

Direct combustion of biomass for heat generation is the most inefficient technique in energy economy, heat being the most inefficient of all forms of energy. The best way to utilize biomass is to recycle biomass for pro­duction of other or further biomass, namely, agriculture, horticulture, aquaculture, poultry, animal farming, and so forth. Randomness is reduced (low entropy change), and environmental chaos is lessened. Properties (a), (c), and (d) are significant for farming; (b) and (f) are important for hydrolytic processes; and (e) is important for biofuels and biodiesel. All the points are important for fermentations and in biore­fineries. Biorefinery has become a new science and technology harmony for a promising future, which takes care of different aspects of biosafety, minimizes waste, and maximizes energy efficiency. It is a field of engi­neering and technology for the future. Biorefinery is a system similar to that of petroleum in its requirements for producing fuels and chemicals from biomass. A biorefinery is a capital-intensive project and is based on a conversion technology process of biomass. Hence, several technologies— thermochemical, chemical, biochemical, and so forth—are combined to reduce the overall cost. Fernando et al. suggest an integrated biorefinery process from bio-oil produced from pyrolysis of biomas (see Fig. 2.12),

which will not only produce sugar but also different by-products and electricity [24]. The process can produce its own power.

Fermentation is equally important. Anaerobic and restricted aerobic digestion with selected algae species allow us to harvest hydrogen and clean fuels, without much loss of biomass and with the least amount of waste products. In an aerobic process, the process is carried out by oxi­dizing the volatile matter into biodegradable organic fractions of solid waste. Air acts as a source of oxygen, and aerobic bacteria act as a cata­lyst. The change occurring during the process may be represented as

Biomass + O2 (Aerobic bacteria) s CO2 + H2O + Organic manure

Anaerobic digestion is carried out by segregating the nonbiodegrad- ables and the biodegradables at the same time. This may be done man­ually or mechanically. The smaller pieces of inorganic materials like clay and sand may be removed by washing the biomass with water. The washed material is then shredded into a size that will not interfere with mixing and may be more amenable to bacterial action. The shred­ded biomass is then mixed with sufficient quantity of water, and slurry is fed into a digester system. If necessary, nutrients like nitrogen, phos­phorus, and potassium have to be added to the digester. The process involves four groups of bacteria in the digested slurry as follows:

1. Hydrolytic bacteria catabolize carbohydrates, proteins, lipids, and so forth contained in the biomass to fatty acids, H2, and CO2.

2. Hydrogen-producing acetogenic bacteria catabolize certain fatty acids and some neutral end products to acetate, CO2, and H2.

3. Homoacetogenic bacteria synthesize acetate, using H2, CO2, and formate.

4. In the final phase, called the methanogenic phase, methanogenic bacteria cleave acetate to methane and CO2.

Water acts as a catalytic agent in methane formation. Thus water is acted upon by enzymes, itself breaking down to hydrogen and oxygen. Hydrogen is used by microorganisms to reduce CO2 to CH4, while oxygen oxidizes carbon dioxide, i. e., makes it acidic (H2CO3). In simple terms, acetate (in presence of CoI) is simultaneously oxidized to CO2 and reduced to CH4. For details, refer to Chap. 1, methanation, and Baker’s and Ganzalus pathway. Thus, methane-forming bacteria play an impor­tant role in the circulation of substances and energy turnover in nature. They absorb CO, CO2, and H2 to give hydrocarbon and methane and help synthesis of their own cell substances. During anaerobic digestion, gas containing mainly CH4 and CO2 is produced. The gas is known as biogas, which is used for the generation of electricity or fuel. The residual biomass comes out of the digester in the form of a slurry, which is separated into a sludge, which is used as fertilizer and a stream of waste water. Research is ongoing to produce renewable energies from different plant sources, which will necessarily dominate the world’s energy supply in the long-term. Using renewable-energy system technologies will create employment at much higher rates than any other technologies would [1]. There are economic opportunities for industries and craft jobs through production, installation, and maintenance of renewable energy systems.