Rural people depend upon biomass fuels such as fire wood, animal waste and crop residues for meeting the demand of cooking and heating. These fuels are burnt in traditional chulhas, causing economic loss to the nation and health problems to women.

Humans domesticated animals and crops that comprise somewhere between 40 to 60% of the earth’s biomass. In many ways biomass can be considered as a form of stored solar energy.

The energy of the sun is ‘captured’ through the process of photosynthesis in growing plants. Carbon dioxide is trapped and carbon biomass increase. When these plants or animals die, a substantial amount of their biomass acts as waste.

Technologies have been developed indigenously to produce modern biomass fuel, such as biogas from cattle dung and other organic wastes and to burn biomass in an efficient manner in improved chulhas.

ADVERTISEMENTS:

Biodegradable waste is such a waste material which is subjected to degradation by microorganisms. Such wastes are biotechnologically being utilised for the production of energy called bio-fuel or bioenergy.

I. Renewable Energy from Biomass :

Biofuel is derived from biomass- recently living organisms or their metabolic by products, such as manure from cows. It is a renewable energy unlike other natural rersources. The carbon in biofuels is extracted from atmospheric C02 by growing the plants.

Both agricultural products specifically grown for use as biofuels and waste from industry, agriculture, forestry and households (including straw, lumber, manure and food leftovers) can be used for the production of bioenergy. Currently, most biofuel is burnt to release its stored chemical energy.

ADVERTISEMENTS:

Research into more efficient methods of converting biofuels and other fuels into electricity utilizing fuel cell is an area of very active work. Bioenergy covers about 15% of the world’s energy consumption. Sweden and Finland supply 17% and 19% respectively, of their energy needs with bioenergy. Biomass can be used both for centralized production of electricity for local heating.

There are many forms of wastes such as solid biomass, liquid and gaseous wastes.

(i) Solid Waste:

Solid forms of biomass that are combustible as a fuel such are: wood, straw and other dried plants, animal waste such as poultry droppings or cattle dung, husks or shells from crops such as rice, peanut and cotton, and sugarcane bagasse.

ADVERTISEMENTS:

(ii) Liquid Waste:

There are also a number of liquid forms of biomass that can be used as a fuel:

a. Bio-alcohols:

Ethanol produced from sugarcane is being used as automotive fuel in Brazil. Ethanol produced from corn is being used as gasoline additives (oxygenator) in the United States. Methanol, can also be produced from biomass. Although this is not economically viable at present.

ADVERTISEMENTS:

b. Biologically produced oils can be used in diesel engines:

Biodiesel obtained from transformation of animal fats and vegetable oil.

(iii) Gaseous Waste:

Methane produced by the natural decay of garbage or agricultural manure can be collected for use as fuel. It is also possible to estimate the number of animals needed for desirable size of biogas driven engine with biogas. Hydrogen can be produced by cracking any hydrocarbon fuel.

ADVERTISEMENTS:

1. Bio-ethanol :

Traditionally, ethanol has been produced by using sugarcane molasses, sugar beet wastes, maize biomass, etc. But on large scale, sugarcane molasses is a good source for production of ethanol.

In recent years, lingo-cellulosic plant biomass has been used in the Brazil and U.S.A. for the production of ethanol. Ethanol blending with petrol to run cars has been successful in Brazil.

Fuel alcohols can be produced from a variety of crops such as sugarcane, sugar beets, maize, potatoes, barley, sunflower, cassava, sorghum, eucalyptus, etc. Two countries have developed significant bio-alcohol programmes: Brazil (ethanol from sugarcane) and Russia (methanol from eucalyptus).

ADVERTISEMENTS:

Brazil is a major grower of sugarcane. It uses sugarcane to produce sugar and to provide the alcohol in making gasohol and biodiesel fuels.

Sugarcane is one of the most efficient photosynthesizers in the plant kingdom, which is able to convert up to 2% solar energy into biomass. It can produce 20 kg for each square meter exposed to the sun.

It is propagated from cuttings. Each cutting must contain at least one bud. The cuttings are usually planted by hand. A stand of cane can be harvested several times; after each harvest, the cane sends up new stalks, called ratoons. It shows a standing crop of sugarcane.

The thick stalk of sugarcane stores energy as sucrose in the sap. Sugar is extracted from this juice by evaporating the water. Crystallized sugar was reported 2,500 years ago in India.

Arabs introduced sugar to the Mediterranean around the eighth century A.D. In 2005, the world’s largest producer of sugarcane was Brazil. Uses of sugar cane include the production of sugar, molasses, rum and ethanol for fuel.

Agricultural alcohol for fuel requires substantial amounts of cultivable land with fertile soils and water.

However, if the fuel alcohol is made of the stalks, wastes, clippings, wheat, potato wastes, cheese whey, rice straw, sawdust, urban wastes, paper mill wastes, yard clippings, molasses straw, corn cobs cellulosic waste, and other crop field trash, then no additional land is needed.

(a) Why Ethanol as Bio-fuel?

Ethanol can reach 96% purity by volume by distillation. This is enough for straight-ethanol combustion. For blending with gasoline, 99.5 to 99.9% pure ethanol is required to avoid separation depending on temperature. These purities are produced using additional industrial processes. Ethanol cannot be purified beyond 96% by distillation.

Today, the most widely used purification method is a physical absorption process using molecular sieves. Ethanol is flammable and pure ethanol burns more cleanly than many other fuels.

It can be said that the combustion of ethanol produces no net CO2. Its combustion products are only CO2 and water which are also the by-products of regular cellulose waste decomposition. For this reason, it is favoured for environmentally conscious transport schemes and has been used to fuel public buses.

Ethanol has a much higher octane ring than ordinary gasoline, requiring changes to the compression ratio or spark timing to obtain maximum benefit. Larger carburetor jets (about 50% larger) are needed to change a gasoline-fueled car into an pure-ethanol-fueled car.

A cold starting system is also needed to ensure sufficient vaporization to maximize combustion and minimize uncombusted nonvaporized ethanol. If 10 to 30% ethanol is mixed with gasoline, no engine modification is needed. Many modern cars can run on the mixture very reliably.

(b) What is Gasohol?

A mixture containing gasoline with about 10% ethanol is known as ‘gasohol’. It was introduced nationwide in Denmark. In 1989, Brazil produced 12 billion litres of fuel ethanol from sugarcane, which was used to power 9.2 million cars. The most common gasohol variant is ‘E10’, containing 10% ethanol and 90% gasoline.

Other blends include ‘E5’ and ‘E7’. These concentrations are generally safe for recent, unmodified automobile engines. Some regions and municipalities make it mandatory that the locally-sold fuels contain limited amounts of ethanol.

Several times suggestions have been given to India also to start blending of alcohol with petrol. This will minimize the pressure on petrol consumption in the world. India is also thinking of starting the gasohol programme.

The term ‘E85’ is used for a mixture of 15% gasoline and 85% ethanol. An increasing number of vehicles in the world are manufactured with engines which can run on any gasoline from 0% ethanol up to 85% ethanol without modification. Many light trucks (i.e. minivans and pickup trucks) are designed to be dual fuel.

They can automatically detect the type of fuel and change the engine’s behavior, principally air-to-fuel ratio and ignition timing to compensate for the different octane levels of the fuel in the engine cylinders.

In Brazil and the United States, the use of ethanol from sugarcane and grain as car fuel has been promoted by the government programmes. Some U.S. states in the Corn Belt began subsidizing ethanol from corn (maize) after the Arab oil imbargo of 1973.

The Energy Tax Act (1978) authorized an excise tax exemption for biofuels, mainly gasohol. Another U.S. federal programme guaranteed loans for the construction of ethanol plants, and in 1986 the U.S. even gave free corn to ethanol producers.

The average cost of production of sugarcane (including farming, transportation and distribution) is US$ 0.63 per US gallon (US$0.17/L). Gasoline prices in the world market are about US$ 1.05 per US gallon (US$0.28/L).

The alcohol industry was invested heavily in crop improvement and agricultural techniques. As a result, average yearly ethanol yield increased steadily from 300 to 550 m3/km between 1978 and 2000 were about 3.5% per year.

One ton (1,000 kg) of harvested sugarcane contains about 145 kg of dry fiber (bagasse) and 138 kg of sucrose. If the cane is processed for alcohol, all the sucrose is used, yielding 72 liters of ethanol.

Burning the bagasse produces heat for distillation and drying, and (through low-pressure boilers and turbines) about 288 MJ of electricity, of which 180 MJ is used by the plant itself and 108 MJ sold to utilities.

Thus a medium-size distillery processing 1 million tons of sugarcane per year could sell about 5 MW of surplus electricity. At current prices, it would earn US$ 18 million from sugar and ethanol sales, and about US$ 1 million from surplus electricity sales.

With advanced boiler and turbine technology, the electricity yield could be increased to 648 MJ per ton of sugarcane. But current electricity prices do not justify the necessary investment.

Bagasse burning is environmentally friendly as compared to other fuels like oil and coal. Its ash content is only 2.5% (against 30-50% of coal), and it contains no sulfur. It produces little nitrous oxides because it burns at relatively low temperatures. Moreover, bagasse is being sold for use as a fuel in various industries, including citrus juice concentrate, vegetable oil, ceramics, and tyre recycling.

3. Biodiesel :

As early as 1853, E. Duffy and J. Patrick conducted transesterification of a vegetable oil many years before the first diesel engine became functional. In 1912, Rudolf Diesel said, the use of vegetable oils for engine fuels may seem insignificant today, but such oils may become, in the course of time, as important as petroleum and the coal tar products of the present time.

During the 1920s, diesel engine manufacturers altered their engines to utilize the lower viscosity of the fossil fuel (petrodiesel) rather than vegetable oil, a biomass fuel. The petroleum industries were able to Standard for biodiesel is IS014214.

Another is the ASTM International Standard ASTM D 6751, which is the most common standard in the United States. In Germany, the requirements for biodiesels are fixed in a DIN standard. There are standards for three different varieties of biodiesel which is made of different oils.

(a) Composition of Biodiesel:

It is an alternative to petroleum-based diesel fuel. It is prepared from renewable resources such as vegetable oils and animal fats. Chemically, it is a fuel that comprises of a mixture of mono-alkyl esters of long chain fatty acids.

The base oil is converted through a liquid transesterification production process into the desired esters where free fatty acids are removed. After processing, biodiesel has very similar combustion properties to petroleum diesel.

It is a renewable fuel that can replace petrodiesel in current engines and can be transported and sold. Use and production of biodiesel are increasing rapidly, especially in Europe, the U.S.A. and Asia. In all markets it makes up a small percentage of fuel.

A growing number of fuel stations are making biodiesel available to consumers, and a growing number of large public transport use some proportion of biodiesel in their fuel.

(c) Properties of Biodiesel:

Biodiesel is non-flammable, and in contrast to petroleum diesel, it is non-explosive, with a flash point of 150°C as compared to 64°C for petrodiesel. Unlike petrodiesel, it is biodegradable and non-toxic.

It significantly reduces toxic and other emissions when burned as a fuel. The most common form uses methanol to produce methyl esters, though ethanol can be used to produce an ethyl ester biodiesel.

Base Oils of Biodiesel:

Soybeans can be processed to produce Biodiesel. Moreover, a variety of biolipids can be used to produce biodiesel. These include: (i) virgin oil feedstock; rapeseed and soybean oils, though other crops such as mustard, palm oil, hemp and even algae show promise, and (ii) animal fats including tallow, lard and yellow grease.

Waste vegetable oil is the best source to produce biodiesel. However, the available supply is drastically less than the amount of petroleum-based fuel that is burned for transportation and home heating in the world.

According to the United States Environmental Protection Agency (EPA), restaurants in the US produce about 300 million gallons of waste cooking oil annually.

Similarly, animal fats are limited in supply. It would not be efficient to raise animals simply for their fat. However, producing biodiesel with animal fat that would have otherwise been discarded could replace a small percentage of petroleum diesel usage.

(d) Soybean Biodiesel:

Soybeans are not a very efficient crop solely for the production of biodiesel. But its common use in the U.S.A. for food products has led to soybean biodiesel becoming the primary source for biodiesel in that country.

Soybean producers have lobbied to increase awareness of soybean biodiesel expanding the market for their product. The United States has produced a Soybus that can run on soybean biodiesel.

In Europe, rapeseed is the most common base oil used in biodiesel production. In India and Southeast Asia, the jatropha tree is used as a significant fuel source. The jatropha seeds contain the maximum amount of oil. Moreover, there is similarity between chemical constituents of jatropha oil and the other oils.

Soybean biodiesel produces 41% less greenhouse gas emissions than diesel fuel, whereas corn grain ethanol produces 12% less greenhouse gas emissions than gasoline.

Soybean has another environmental advantage over corn because it requires much less nitrogen fertilizer and pesticides. These agricultural chemicals pollute drinking water, and nitrogen decreases biodiversity in global ecosystems.

II. Biogas (Gobar Gas) :

Energy is the basis of all live forms on the earth. Everyone needs energy in one form or the other form, whether it is human beings, animals or plants. Energy is needed not only for the survival of the mankind but also for growth of a country.

Higher the consumption of energy, higher would be the growth of the country. Because socio-economic development of a nation depends on the availability of energy and energy consumption.

At present the most commonly used energy resources all over the world are: oil, gas, coal, etc. Several countries have been able to utilize the nuclear energy to meet their energy requirements.

India has to use the available conventional sources judiciously but also harness the non-conventional sources of energy. The most commonly available non-conventional sources of energy are: biogas (gobar gas), solar, wind, biomass, etc.

Biogas has been developed and is being utilized to the maximum extent in our country. The largest cattle population in warm climate in major part of the country for most of the year makes the simple biogas technology highly successful in our country.

The Khadi and Village Industries Commission (KVIC) (Mumbai) initiated implementation of family size biogas plants of size ranging from 23 per day capacity to 103 per day capacity in the year 1961-62. Since KVIC was the only agency implementing the programme at that time and has designed a model, it is known as the PIONEER in the biogas field.

The prime motive for the Commission to implement the programme was to reduce the drudgery of women in cooking on inefficient smoky fuels besides generation of employment in the rural areas as well producing manure in that process.

Now, in the country so far around 6 lakh family size plants are constructed by the KVIC alone.

A scheme of installing large size biogas plant was implemented from 1991 as per the financial pattern of Ministry of Non-Conventional Energy. Up to 2002-2003, KVIC installed around 1400 large size Plants in the country.

This programme is widely accepted by the institutions, Gurudwaras and also other Goshalas, etc. It shows the cattle which provide cow dung to be used for burning dry dung cakes, and biogas production.

Biogas technology provides an alternate source of energy in rural India to meet the basic need of cooking in rural areas. By using local resources viz., cattle waste and other organic wastes, energy and manure are derived.

In the late 1970s, realization of this potential and the fact, that India supports the largest cattle wealth, led to the promotion of National Biogas Programme.

The Ministry of Non-Conventional Energy Sources continues to implement a centrally sponsored scheme National Biogas and Manure Management Programme (NBMMP). A modified version of the Ninth Plan Scheme on National Project on Biogas Development (NPBD), with the objectives to promote family type biogas plants and biogas power stations is also in progress.

1. Construction of a Biogas Plant:

India is a leader country in biogas technology. There are perhaps millions of gobar gas plants in India. A long-term goal is to have one at each of our homes. Two types of plants are constructed: fixed dome type and floating drum type.

The technology is very simple and used friendly. A plant consists of an inlet tank, digester, outlet tank, and gas distribution system.

First a ten feet deep pit is dug. Then a water-tight cement cylinder (with brick or gravel) is constructed. A wall is built across the middle, extending up from the bottom, not quite to the top. Intake and outgo pipes are installed. The whole unit is made water-tight. This is called ‘fixed dome biogas plant’.

A second type of biogas plant is also installed where floating metallic tank is prepared. A pit of defined size is dug and cemented side walls are constructed. A metallic tank is fabricated which has inlet and outlet knobs. It is called ‘floating drum biogas plant’. Cow dung slurry is prepared and transferred into the pit.

The manure is mixed with water in the intake basin to make slurry (Fig. 11.35) which goes down the pipe to the bottom of the left side. This side of the cylinder gradually fills and overflows to the right side. Meanwhile, the whole mass bubbles methane up to the top. It collects under the large metal bell-like cover. The gas builds pressure, and can be taken off through a rubber tube to a gas stove in a kitchen.

When both sides of the cylinder are full, the effluent flows out from the bottom of the right side. Each time more raw manure is added to the left. Under anaerobic conditions, in the presence of methanogenic bacteria, the cowdung/cellulosic wastes undergo bio-degradation producing methane-rich biogas and effluent.

2. Anaerobic Degradation of Residues:

Methane production by methanogenic bacteria is called methanogene sis. Organic manure (cowdung, plant and animal wastes, plant leaves, etc. undergo biological anaerobic degradation of residues. This process can be divided into four steps:

(i) Hydrolysis:

High weight organic molecules (like proteins, carbohydrates, fat, cellulosic) are broken down into smaller molecules like sugars, amino acids, fatty acids and water.

(ii) Acidogenesis:

Further breakdown of these smaller molecules occurs into organic acids, carbondioxide, hydrogen sulfide and ammonia.

(iii) Acetagenesis:

The products from the acidogenesis are used for the production of acetates, carbondioxide and hydrogen.

(iv) Methanogenesis:

Methane-producing bacteria are called methanogen. Finally, methane, carbondioxide and water are produced from the acetates, carbon dioxide and hydrogen (products of acidogenesis and acetagenesis).

There are several groups of bacteria that perform each step. In total dozens of different species are needed to degrade a heterogeneous stream completely. Most of these bacteria adhere to the substrate prior to extensive hydrolysis.

Pathway of methane formation is given in. Hydrogen-producing acetogenic bacteria are one of the important groups in biogas digesters. These organisms oxidize the fatty acids that are longer than acetate and thereby release energy from the substrate in the form of methane.

Digester slurry contained higher cellulolytic population of bacteria, while the outlet of the digester recorded the least cellulolytic bacterial population.

Methanogens (methane producing bacteria) possess very limited metabolic properties, using only acetate or C1 compounds (H2 and CO2, formate, methanol, methylamines or CO). Methane is the end product of the reaction. Of the methanogenic genera, Methanosarcina sp. and Methanosaeta sp. form methane by aceticlastic reaction. Faster-growing Methanosarcina sp. is predominant in the digester.

3. Uses of Biogas and Sludge:

(i) Biogas Power Projects:

Biogas can be utilized either for cooking / heating applications or for generating motive power or electricity through dual-fuel, gas engines, low pressure gas turbines or steam turbines (Fig. 11.37). It is estimated that about 100 metric tons of cattle dung available per day from about 16,000 cattle would be adequate for a 300 kW power station.

At each for treatment, 50 metric tons of cattle dung per day would be required. This shows huge potential for setting up biogas power projects in large gaushalas (cow shades) and dairy farms.

(ii) Sustenance of Soil Fertility:

The sludge from anaerobic digestion, after stabilization, can be used as a soil conditioner, or as manure depending upon its composition, which is determined mainly by the composition of the input waste. Increased crop yield has been found after use of sludge as manure.

In Kerala, digested slurry is directly used in coconut plantation. Increased grain yield of black-gram by 80.5% has been recorded with addition of 40 tonnes/ha slurry together with recommended dose of NPK.

(iii) As Carrier for Microbial Inoculants:

Moreover, the spent slurry can be used as carrier for preparation of Rhizobium-based biofertilizer. Shelf-life of Rhizobium in immobilized spent slurry has been found for about three months.