Adequate supply of energy at a reasonable cost is the key factor to the economic development of a country. The fossil fuel reserves are fast depleting and the world is realising about the energy crisis in the future. It is important to formulate a broad-energy policy, taking into consideration a variety of sources and options. At this juncture the bio-mass becomes prominent as a future source of energy. This booklet describes about the various sources of biomass in India and highlights their fuel value.

I. Introduction

The steep increase in the cost of oil and the uncertainty of its availability is being realized all over the world. In order to meet the future energy need it is necessary to develop and use the non-conventional sources also. Among a number of options available, biomass is one of the potential sources of energy as solid, liquid and gaseous fuel. Fuel from biomass is  obtained from a variety of fuel stocks such as wood, charcoal, dung, vegetable, water, etc. More than one third of the world's population depends on wood for cooking and heating. But increased population, industrialization and urbanization have encroached upon forest land, thereby creating wood fuel scarcity. The woods available with us is not sufficient to meet the demands of timber, pulp and paper industries. Therefore, alternatives are to be searched for. Among the biomass sources, wastes and weeds are available in bulk, almost free of cost and the fuel value of these is not utilized properly. If utilized in a right way, they can meet 75% of the demands of the rural population in India. By a number of technologies, wastes and weeds can be converted to solid, liquid and gaseous fuels, which can be used for cooking, lighting, heating, pumping water, fuel for industry, transport and electricity generation. For more details about conversion methods refer booklet No.379 on "Biomass as a source of energy"

II. Wastes and Weeds in India

Wastes and weeds are available in plenty from fields in our country. They are classified and described as follows. 

A. Classification of wastes

Wastes are classified depending on the source from which they are obtained.

1. Agricultural and agro-industrial wastes

The production of agro-residues is increased significantly and the availability is more at the village level. Agro-industrial wastes are also available in plenty about 40 million tonnes a year.

1. Agricultural residues

Annually, 15% of the total residues available per house hold are utilized for fuel purposes. The major agricultural residues for energy production are given in table: 1 here.

Agricultural residues for energy production

Of the total crop residues in India, 74% are available from Uttar Pradesh, Punjab, Madhya Pradesh, Andhra Pradesh, Bihar, West Bengal, Maharashtra and Tamil Nadu. Almost 60% of total crop residues are available during October-December and another 25% during April-June. They contain essentially cellulosic materials, carbon, oxygen, hydrogen and minerals. Direct burning of these residues have a calorific value of 3000-5000 kilocalories per kilogram. They can be pyrolysed to yield charcoal, and methanol, hydrolysed to alcohol and fermented to biogas to be used as a fuel.

1. Agro-industrial wastes

About 79% of these wastes are available from Uttar Pradesh, Andhra Pradesh, Tamil N adu, Maharashtra, Karnataka, Punjab and Gujarat. Important wastes are rice husk, bagasse, molasses, coconut shells, coconut husk, cotton dust, jute mill waste, etc.

iii. Food industry wastes

During the processes of canning, drying and preservation of fruits and vegetables, their peels, cores, pits, vines, stems and other materials accumulate. A bulk of peelings and fruit cakes (matter left after juice extraction from fruit) are available at fruit juice shops on urban areas. Almost in every house we find vegetable peelings.

2. Animal wastes

Among animal wastes, dung, poultry, and sheep droppings and other wastes are used for fuel. In our country, about 1300 million tonnes of dung is available annually from all types of animals. Of total dung 84% is cow dung and buffalo dung and 13% goat and sheep droppings. About 58% of the total dung produced in India, is contributed by Uttar Pradesh, Rajasthan, Madhya Pradesh, Maharashtra and Andhra Pradesh. Dung is put to use as dung cakes and biogas for fuel purposes. Other than this, in general, cattle shed wastes, fisheries, prawn and frog wastes, slaughter; house wastes are the other animal wastes.

3. Forestry wastes 

In recent times, forest or wood wastes is assuming greater importance as fuel. Sawdust is forest based industry waste. Wood chips, dried tree branches, tree twigs, tree bark, leaf litter etc constitute the forest wastes. 

4. Industrial wastes 

Industrial wastes other than agro-industrial wastes can also be used for fuel production. Industries like paper mills, chemical industries, oil refineries, cotton mills, dairy industry generate various types of wastes (by-products) which contain sufficient amounts of energy.

Plastic wastes, paper wastes, textile wastes etc have good calorific value. They are also useful to produce biogas and electricity generation. 

5. Municipal wastes

These are the main wastes in towns and cities. Municipal and sewage wastes include sewage and sludge, garbage, horse dung, cattle dung and wastes from animal slaughter houses. Garbage potential of Indian cities is estimated about 41,000 tonnes per day and the annual production is 15 million tonnes. Garbage can be converted an aerobically to biogas and in turn to electricity.

B. Classification of weeds

Weeds can grow any where in the field on their own and compete with the crop plants for nutrients and water. They are considered as nuisance but recently their energy value has been realized by the scientists. 

1. Temstrial weeds

Stems of terrestrial weeds in dry conditions may be used for burning. The Zizyphus sotundifolia, Calotropis procera, dantana cameraekare are cut, dried and used as a fuel. A large number of latex yielding weeds can be used as fuel for diesel engines. 

2. Aquatic weeds

Aquatic weeds constitute a highly productive crop that requires no tillage, fertilizer, seed or cultivation. They can be used for biogas production. The high moisture content of these weeds is the helpful feature for biogas production.

III. Agricultural Wastes

These wastes are available from different sources. 

A. Commercial crops

Coconut, cotton, coffee,etc are the commercial crops, wastes of the same and their characteristics are given here.

1. Coconut wastes

 Million tonnes of coconut shells are reported to be available in the country each year. The output of charcoal from 1000 shells is 35 kgs; in other words 30,000 shells yield one tonne of charcoal and the process followed is destructive distillation. Husk and shell can be gasified to yield producer  gas which can be used for dual-fuel engines. Husk can be used as a feed stock for alcohol production. Coconut coir can be pyrolysed to produce cocogas which can be used as diesel engine fuel. Coir dust (60%) along with cow dung (40%), produces biogas for fuel purposes. 

2. Coffee wastes 

Spent coffee grounds can be used as feed stock for methane production by anaerobic digestion. Pulp can be used for gas production along with cow dung. Though 3-4% of alcohol can be produced from coffee pulp, it is not economically feasible. It is a good starting material for methanol production. 

3. Cotton wastes

Cotton stalks can be carbonized to char, which is suitable for briquetting and can be used as a smolders fuel. They can be hydrolysed and fermented to alcohol. Cotton bolls and hulls are used as a smokeless fuel in rural areas. Broken cotton seeds, linters, leaves and other plant parts named gin waste which has a very high fuel value and used as a house hold fuel.

B. Fruits and vegetables

Fruit and vegetable industry wastes can be converted into several energy products like biogas, alcohol and solid fuel briquettes. 

1. Fruit industry wastes

 Large quantities of wastes from different fruit industries are mentioned here. 

1. Apple wastes

Apple processing results in large quantities of waste accumulates known as pomace. For briquetting 1:1 mixture of coal and pomace can be used which has been found to give briquette best suited for use as fuel in smokeless chulha. For biogas production 2:3 ratio of pomace and cattle dung are used. 

1. Banana wastes

Banana stem is allowed to go waste after harvesting is over. It can be subjected to decomposition in closed containers which yields inflammable biogas which is used for domestic lighting and cooking. Banana peelings, rotten bananas are also used for energy production.

Apart from this, orange peels, papaya and peach wastes, pine apple wastes can be converted an aerobically to methane. Citrus fruits after processing for juice, leaves behind 45-60% fruit waste in the form of peel rag and seeds which can be used for alcohol production. Peel and kernels of mango can also be used as raw material for alcohol production. 

2. Vegetable wastes 

Different wastes of vegetables yield fuel. An aerobic digestion of cabbage wastes of 35°C at neutral pH can be carried out to produce biogas. The optimum proportions are 70% cabbage wastes, with 30% sewage sludge and 95% liquid cabbage wastes with 45% manure. Sweet potato stalks and leaves can be fermented at 37°C for 10 days to produce 70% methane containing bio-gas tomato solid wastes and kitchen wastes also produces biogas when fermented. Pyrolysis of ladies finger leaves and stems gives charcoal having a calorific value of 4421 Kcal per kilogram. Tomato stems and leaves on pyrolysis also yield charcoal of 4389 kcals per kilogram.

C. Oil seed crops

 Main oil seed crops and their importance in producing fuels are given here. 

1. Groundnut 

Shells contain 32% cellulose and can be easily converted into liquid fuel after hydrolysis. It can be fermented in the presence of yeast at 30°C for 24 hrs for ethane production. Straw of groundnut can be used as a fuel after briquetting. 

2. Rapeseed and mustard stalks 

For every tonne of rapeseed and mustard seed produced, about 1.8 tonnes of stalks are produced. Mustard stalks on pyrolysis yield charcoal having a calorific value of 4421 kcals per kilogram. 

3. Safflower

Stalks of safflower are widely used as fuel in rural areas. Hulls are rich in fibre which can be hydrolysed and fermented to yield alcohol. The hulls are a good fuel for direct burning. It has a calorific value of 4565 kcals per kilogram. 

4. Castor and linseed 

Castor sticks and leaves are a good fuel where as stalks of linseed have a good calorific value.

5. Sunflower

The stalks are mostly used as a household fuel which can be converted to briquette which have higher heating value 3900 kcals/kilogram. The sunflower husk can be converted c into pellets (4498 kcals/kg of heating value) which have c\ higher heat content than stalk briquettes.

The stalks on pre-treatment with per acetic acid gives higher yield of alcohol. The stalks after pre-treatment yield sugary syrup which on fermentation yields ethanol. 

D. Pulses 

Stalks of arhar (pigeon pea) are used extensively as a domestic fuel in villages with a heating value of 3700 kcals/ kilogram. About 50% of the stalk composition is cellulose. Stalks burn steadily and can be used for gasification.

Gram straw produces energy which has a heating value of 3800-3900 kcals/kilogram. It can be used in a briquetted form.

Soybean seed coats are rich in lingo-cellulose and can be used for ethyl alcohol production. Straws of urd, moong, masoor etc find use as fuel while their calorific values are 3800, 3820 and 3810 kcals/kg respectively.

E. Cereals

Rice is one of the major cereal crops of India. During the milling of rice, husk and bran are obtained as by products.

1. Rice

Rice husk is more important than bran as it has more calorific value compared to bran which ranges from 2940- 3460 kilo cals/kilogram. Three kilograms of this residue has the same calorific value as 1.5 kg coal or1 kg fuel oil. It has high silica content, ash content and 12-17% carbon and 15- 18.5% ash as fuel properties which makes it easy for complete combustion to produce energy. Rice husk produced energy is useful for furnaces, for large-sized rice mills, for dehydration industries, for tobacco industry, brick kilns etc. In post-harvest operations also rice husk energy is used.

Rice straw has a high energy value of 3000-3500 kcals/ kg which can be devesified to fuel briquettes. It can be hydrolysed and fermented to ethanol. Powcr can also be generated from the straw at a cheaper rate compared to thermal plant. With cattle dung and rice straw (1:2) produces biogas.

2. Maize

Among maize residues, maize cobs and maize stalks are widely used as fuel in rural India. Maize cobs comprise about 30% of maize grain. They can be directly burnt as fuel having a heating value of 3500 kcals/kilogram. Charcoal from cobs can be made by burning a sack of com cobs in a oil container (drum) completely till a smokeless flame is attained. Then, this completely burnt charcoal is spread over the floor and quenched with water to avoid further combustion. It is allowed to dry under direct sunlight. Sieving can be done to let out the loose portions and charcoal is collected and stored.

Cobs having 15-25% moisture can be gasified at 200-300°C temperature by reduction in a gasified. Producer gas is the resultant gas.

Cobs can be pre-treated with sodium hydroxide and these are fermented enzymatically to produce ethanol. Maize stalks can also be used as fuel.

3. Others

Bajra stalks and leaves are a good fodder, but in emergencies they can be used for fuel purposes The stalks have a heating value of 3850 kcals/kilogram. Barley straw when supplemented with dairy manure produce biogas by anaerobic digestion. Jowar straw (mixture of stalks and leaves) can be used as a fuel in dried form. Oat straw can be pyrolysed to give charcoal and producer gas.

F. Sugar crops

Sugarcane and sugar beet are the important sugar crops.

1. Sugar cane

Sugarcane trash is the only residue from its production, where as bagasse, molasses and pressmud are the milling industry residues.

Sugarcane trash is dried sugarcane leaves and constitutes one-tenth of the total sugarcane production. For electricity production, sugarcane tops and leaves aloe shredded and juice extracted. The fibrous residue with 50% moisture is combusted to produce high pressure steam, which is used for electricity generation in turbo alternators. Briquettes made from trash are a better fuel than biomass burning directly.

Bagasse is the fibrous residue left after the extraction of juice from sugarcane. Reduction of moisture in bagasse improve its calorific value. Well-wet bagasse (48% moisture) has a calorific value of 1890 k cals/kg whereas dried bagasse (30% moisture) will have a calorific value of 3000 kilocals/ kilogram. Completely dried bagasse can be burnt with a high efficiency and is a valuable raw material for the production of pulp and paper production. Bagasse can be used for power generation the entire quantity produced in India is used in sugarcane factories for generating steam in boilers.

Cane molasses is a basic raw material for alcohol production in India. Alcohol is used in chemical industry and also used as an engine fuel.

Pressmud with cow dung produces bio-gas. Methane content of bio-gas. Methane content of bio-gas is contributed in large amounts from pressmud (70%) than cow dung (55-60 per cent).

Sugarcane pulp is also anaerobically digested to yield biogas.

G. Miscellaneous

Among the miscellaneous crops, jute is the most important one. The sticks and dust of jute are used for fuel purpose. Sticks form the core of woody part of the plant and are rich in cellulose. A good quality smokeless charcoal in chip form can be made by its low temperature carbonization. Medium grade charcoal having 80-88% carbon may be used in gunpowder compositions for making smokeless briquettes for domestic fuel. They can also be hydrolysed and fermented to yield ethyl alcohol.

Jute dust constitutes 1/10th of the jute produced. It has a calorific value of 4000 kcals/kg and used as a fuel in boilers of jute milling industry. About 98% of jute dust is utilized for the jute milling industry itself. The energy conserved per jute mill from jute dust is 11.6% of the total energy conserved.

Tapioca residues can be digested aerobically to yield bio-gas. Stalks of daincha are also dried and can be used as fuel. They have a heating value of 3500 kilocals/kilogram. Ragi straw can also be burnt efficiently.

IV. Industrial Wastes

A large number of industrial wastes potential for energy production fall under agro-industrial wastes such as rice husk, bagasse, molasses, etc. In addition there are paper, leather, textile, plastic and rubber wastes which can be used for fuel production.

1. Paper wastes

Gasification products of special grade paper wastes are better in fuel value than the products from waste paper from municipal solid wastes, and dried primary sludge from paper mill effluent treatment plant. The calorific value of special grade paper is 8000 kilocal/kilogram. And also, pyrolysis products from this paper have better fuel values than other two types of paper wastes. Bio-gas can be produced from effluent sludge of paper mills.

Cotton textile mills, mainly their blowing rooms generate large quantities of waste. Since this waste is rich is cellulose, it could be used for bio-gas production. Willow-dust (trash from cotton processing in textile mills) is pre-treated with 1.5% urea solution for 3 days and digested to produce methane.

V. Animal Wastes

Among animal wastes, dung is more important than any other wastes. For fuel purposes, dung, urine, poultry excreta are mainly used.

Animal dung fom1s about 8-10% of the total energy consumption in the rural areas. Dung cakes are used as fuel by direct burning. The 'calorific value of fresh dung on over dry basis is 2823 kcals/kg for buffaloes. 3062 and 3565 kilocalsl kg for cows and pigs respectively.

Cow and buffalo dung are the best types of dung for cooking. When made into cakes and dried, they burn for a longer time with steady flame. In Rajasthan, camel dung is used for fuel purposes.

Due to its homogeneity and particulate nature, cattle dung serves as a better substrate for anaerobic digestion to produce bio-gas. Presently, utilization of dung for bio-gas production is being popularized. More than 7lakhs of bio-gas plants have been installed in India which shows the importance as fuel. Bio-gas out-put can be increased by the addition of other organic residues and wastes to cattle dung. For example, a mixture of cattle dung and rice straw (1:1) yield 9.1 % more bio-gas than rice straw alone.

VI. Forest Wastes

Forests in our country are not evenly distributed. In some parts where population is sparse, like in Andaman and Nicobar Islands, dense forests yielding surplus wood are present. On the other hand in thickly populated areas like Uttar Pradesh (Gorakhpur), even dried leaves and twigs are brought from the forest for fuel purposes. Faulty felling and cross cutting technique also results in lot of wood waste. Saw dust is produced from saw mills. Thus, forest wastes comprise, logs, chips, barks, leaves and saw dust. Mostly available from the states Madhya Pradesh, Himachal Pradesh, Andhra Pradesh, Bihar, U.P. and Orissa. Heating value of wood waste is between 2500-3850 kilocals/kg and bark shows a heating value range of 2500-2850 kcals/kilogram. Saw dust and wood chips are combusted in boilers, stoves and furnaces. But the thermal efficiency is low. It can be increased by gasification of these wastes and making saw dust briquettes. They both can either be fermented to produce biogas or gasified to yield produce gas. Wood waste can be used for power generation through combustion or gasification.

In the forests of sub-Himalayan region, pine needles which are the wastes of the pine forests are abundantly present. Per hectare per year availability of pine needles is estimated as 1-2 tonnes. These can be collected and converted to char and gaseous fractions by low temperature pyrolysis (200- 400°centigrade). The gaseous products contain gases with high fuel value.

VII. Municipal Wastes

Municipal wastes includes municipal solid wastes (MSW), night soil and waste waters.

A. Municipal solid wastes

Municipal wastes can meet the energy needs of the urban areas if utilized properly. In India, per day collection of MSW is 0.4 kg and it is expected to increase with increasing population. To avoid environmental pollution problems and to meet urban areas energy needs, the MSW should be composted. But the non-compostable fraction of the municipal solid wastes has become a problem. To overcome these problems, other methods like pyrolysis, gasification are adopted to produce methane. The calorific value of MSW is 2572 kcals/kilogram.

B. Night soil and waste waters

In India, night soil or human waste is fermented to yield biogas. The waste waters from sewage can also be used to produce sewage gas. It contains methane and carbon monoxide which is comparatively better than gober gas. Its calorific value if 5640 kcals/m3 and it can be used in diesel engines.

VIII. Terrestrial Hardy Weeds

Terrestrial weeds can also be used for fuel purposes. Different species of weed that can be used are given here.

1. Besharam

Besharam is scientifically known as Ipomea fistulosa. It is a semi-woody plant propagated by cuttings. Its wood is used as firewood. It regenerates quickly after coppicing due to presence of growth hormones in milky juice of fistula stems. Its biomass yield can be optimized by coppicing at regular intervals. It is reported that these cuttings each year not only enhance biomass yield but also ensure its better survival under natural climate.

2. Chetak chandni

It belongs to the family compositae and it is also known as congress weed, carrot-grass etc. Its scientific name is Parthenium hysterophorus. Dried biomass of this weed on pyrolysis produces charcoal. It can be compacted in the form of pellets which on burning gives no smoke.

3. Four 0' clock plant

Belonging to the family Nyetaginaceae Mirabilis jalapa is a herb grown in pots, shrubberies or perennial borders. The leaves of this weed contains a C/N ratio nearly 30 which is optimum for biogas production. Anaerobic digestion of the leaves can produce 400 litres of bio-gas per kg of dry matter. The methane content of bio-gas from the leaves is 69 percent. The sterns and roots are often used as domestic fuel in rural areas.

4. Lantana

Lantana camera is rated as one of the world's 10 worst weeds. But, twigs, wood are used as fuel. Twigs are used as a fuel for cooking and heating and its wood is also among good fire woods. Its hard wood have a calorific value of 4433 kilocals/kilogram. The wood on pyrolysis gives charcoal with heating value of 624 kilocals/ kilogram. Seven kg of dry wood can yield about 2.5-3 kg carbon powder (charcoal). It can be made into pellets with 10-15% clay or dung. Its leaves yield 40 litres/kg of biogas which contain 68% methane. Alkali (1 % Na OH) treated lantana residue with cattle dung in the ratio of 1:1 at 28 to 31 DC, yields more bio-gas than cattle manure alone.

5. Munj

Munj (Saccharam munja) is a perennial grass whose wood can be better used in the form of charcoal. It can be produced by pyrolysis and will have a calorific value of 3892 kcals/kilogram. The charcoal can be made into pellet by mixing it with 10-15% clay or gobar.

IX. Petroleum Weeds

The plants which accumulate the photosynthesis products (hydrocarbons) of high molecular weight (10,000) known as petroleum weeds.

1. Calotropis

Calotropis gigantea is a shrub which can be burnt directly for fuel. Direct stem wood is rich in hydrocarbons which can yield liquid fuel. High molecular weight compounds can be hydrocracked to yield gasoline, diesel oil and lubricants. The residual biomass can be utilized to get briquetted fuel, biogas, methanol, or ethanol.

2. Euphorbias

Member of Euphorbiaceae family has hydrocarbon molecules in their latex with 20,000-50,000 molecular weight. The gopher plant (Euphorbia lathyris) has both terpenoids and sugars. Terpenoids can be converted to gasoline like substances where as sugars can be fermented to alcohol which can be used as fuel. Thus, the plant has dual energy potential. Other species like Euphorbia tirucall, E.anthisyphilitica, E. aetea, can also yield high fuel value extracts.

The utilization of petroleum weeds will depend on the progress that can be achieved in

1. the scope for use of these extractable as chemical feeds stocks for industries,
2. the conversion of extractable into low molecular weight liquid fuels, in on the energy crop yield obtainable per hectare of land. Thus, the role of petro-crops is unique in the field of bioenergy production.

X. Aquatic Weeds

Many aquatic plants like Salvinia, water hyacinth, and lower plants like algae are also used for fuel production.

1. African payal

African payal (Salvinia molesta) is a free-f1oating aquatic fern which can be used for bio-gas production either directly or with dung. Anaerobic digestion in commercial digesters yield biogas with 40- 78% methane. When the biogas production is made in the presence of zinc, a 33 per cent enhancement is observed.

2. Water hyacinth

Eicchornia cvassipes is also a free-floating plant and it can produce 17.8 tonnes of biomass per hectare per day. Its C/N ratio ranges between 18-26 which is optimum for the bio- gas production. For that, the plants are collected and sun-dried. The dried material is powdered in a mill. In the mill, the soil is mixed with water hyacinth powder for proper sedimentation. Introduction of soil increases the micro-flora. In general 4.5-6.3% slurry gives maximum biogas production. One kg of water hyacinth can yield 37 4litres of biogas containing 60-80% methane.

Water hyacinth takes 3 days for decomposition during summer and 4 days in winter season when compared to 8 and 12 days respectively for cow dung decomposition. However, 1:1 ratio of water hyacinth and cow dung gives maximum gas production than either of the substrate.

Utilization of water hyacinth for gas production has gained considerable momentum in India. Agricultural universities are also working On this. Biogas produced from this plant can be used for cooling, heating, lighting and even as a. source of power for engines, tractors, cars, etc.

3. Water lettuce

Pistia stratioles is also known as a duck weed which is a very good substrate for biogas production. A mixture of cow dung, water lettuce and water in the ratio of 1:2:1 yield good quality biogas. The average methane content is 58 to 68 percent.

4. Water spinach

Water spinach can also be used for biogas production. Leaves of this wild plants are used for this purpose. They contain 90% moisture. Along with cattle dung it produces better yield of biogas.

5. Algae

Algae are grouped into brown algae (Pheophyta), red algae (Rhodophyta), green algae (chlorophyta) and blue-green algae (Cyanophyta). These when subjected to anaerobic digestion delays and produce biogas. The fuel value of algae producing biogas is 4900 kcals/ cubic metres. Green algae and blue green algae can produce hydrogen directly which has a greater importance as fuel. Fuel oil also can be yielded from the algae.