Transformation of sugars into alcohols by fermentation is a common practice. Fermentation is carried out by a group of living organisms: yeasts or bacteria. Ethyl alcohol, commonly known as alcohol is one of the most important and popular industrial fermented products. It is a liquid fuel, and can be used as an alternative to automobile fuels. The sugar enriched materials like cane sugar, beet sugar, fruit sugar, potato, com, rice or any other crop of high sugar contents can be used as substrates mainly, along with starchy and ligno-cellulosic materials.

A Materials for fermentation
Following are the types of substrates used for alcehot production.

1. Sugary materials
Examples of sugary materials like sugarcane and its biproducts (bagasse, molasses) and sugarbeet, fruit juice, sweet sorghum, sweet-potatoes etc. Sugarcane molasses is largely being used in many countries for alcohol production. The yield of ethanol is directly proportional to the amount of sugar present.

2. Starchy materials
Tapioca, maize, wheat, barley, oat, sorghum, rice and potatoes are the starchy materials that are used in ethanol production. It has been estimated that 11.7 kg of corn starch can be converted into about 7 liters of ethanol.

3. Lignocellulosic materials
The sources of cellulose and lignocellulosic materials are the agricultural wastes and wood. On the basis of technology available today, about 409 litres of ethanol can be produced from one tonne of lignocellulose.

B Process of fermentation
Micro-organisms can grow on carbohydrates such as sugars, under anaerobic conditions. During anaerobic growth, sugars or other fermentable carbohydrates are oxidized and ethyl alcohol is produced as a product of the fermentation process. Optimum temperature requirement for alcohol production is 30-38°C and optimum pH ranges from 3 to 8. Proper balance of macro (nitrogen, phosphorus, potassium, sulphur etc.) and micro (iron, zinc, manganese, copper etc.) nutrients are required for the growth of micro-organisms.

When fermentation is over, which normally takes 4-10 days, the resultant product consists of a mixture of alcohols and water. Ethanol (ethyl alcohol) can be recovered by distillation process i.e. vaporization of alcohol-water mixture.

XI. Production of Biomass


Biomass production can be studied under these sub-heads.

1. Energy plantations
Energy plantation is the practice of planting trees, purely for their use as fuel. Terrestrial biomass i.e. the wood plants has been used since long time to generate fire for cooking and other purpose. In recent years, to meet the demand for energy, plantation of energy plants has been re-emphasized. Government has started many plans like afforestation, agri-horticultural practices etc.. It has been estimated that at present, only l/7th of the world's total energy comes from biomass and a large amount of it remains untapped. In view of getting maximum biomass afforestation, forest management systems will have to be developed. These must include social forestry, silvi-culture tree-use systems, drought tolerant, salt tolerant, pollutant resistant plantations and high density energy plantations.

Annual plants in energy plantations should have fast growth, stress resistance, less palatable to cattle and other animals, high calorific value, absence of deleterious volatiles when smoke comes out, high yield of biomass and should be disease and pest free.

2. Social forestry
Plantation through social forestry has been much emphasized by the government of India to meet the demand of fuel and fodder in rural areas. This includes planting trees along road sides, canals, railway lines and wastelands in village. Some of the important plants are Acacia nilotica, Albizia lebbek, Cassia fistula, Eucalpytus globulus, Ficus glome rata, Morus alba, Ferminalia arjuna etc.

3. Silvi-culture energy farms
These are known as short rotation forestry. These silviculture farms employ techniques more similar to agriculture than forestry. The chief objective of energy plantation is to produce biomass from the selected trees and shrub species in the shortest possible time (generally 5-10 years) and at the minimum cost, so as to satisfy local energy needs. This would certainly relieve the pressure on the consumption of fossil fuel like kerosene and prevent the destruction of plant cover, which is one of the primary component of life support system. Due to its high yield per unit area, smaller land requirements for biomass output, shorter life span, increased labour efficiency are the advantageous to adopt silviculture.

Different sources of biomass, their forms, their conversion process to respective forms of. energy are given in Table no. 4.

Sl.No	Sources of biomass	Forms of biomass	Conversion process	Forms of energy
A	Plantations
1	Siviculture	Fire wood	Combustion	Heat
2	Energy plantation	-do-	Destructive distillation	Charcoal
3	Agriculture	Carbohydrates		Ethanol
4	Energy crops	Hydrocarbons	Fermentation	Fuel oil
5	Aquatic biomass	Aquaculture		Methanol
6	Weeds	Whole plant body		Methane
B	Residues/wastes/weeds
1	Rural/urban wastes/ industrial wastes		Combustion	Fire/fuel
			Pyrolysis	Fuel oil
			Fermentation	Ethanol
2	Forestry wastes	-do-	Combustion	Fuel
			Pyrolysis	Oil gas
			Gasification	Gas
			Fermentation	Ethanol
3	Agricultural wastes	Wastes	Fermentation	Methane
4	Weeds & aquatic biomass	Wastes	Fermentation	Methane
5	Cattle dung	Wastes	Fermentation (biomass)	Methane

Thus production of biomass helps in developing cheaper source of energy from unutilized agricultural residues, wastes, forest wastes, plantations etc. which is an alternative source of energy for fossil fuel energies.

First : Biomass as a source of energy