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Utilization of post-harvest residues

Bharat Bhushan
Regional Research Laboratory, Hyderabad, India


During the period of colonial rule, the traditional balance between agriculture and rural industry was disrupted, and India, like other colonies, became increasingly specialized in the production of primary commodities that were further processed in the metropolitan countries. The colonies served as markets for finished goods. This process was accomplished by fostering a feudal-type system in the colonies when feudalism was giving way to industrial societies in the colonial powers. Thus, in the course of time, the independent economies of colony countries were changed into dependent ones complementary to the economies of the metropolitan countries.

The base of the economy in India and other developing countries continues to be agriculture. The dominant features of the economies of countries that were formerly colonies are:

1. high annual rate of population growth and high density of population in fertile regions;
2. high percentage of small landholders using labour intensive, traditional farming techniques;
3. high post-harvest losses, largely due to inadequate storage facilities and practices;
4. generation of enormous quantities of agricultural residues that are inadequately utilized, either because they are widely dispersed and not readily available, or because there is a lack of technological information on how to use them;
5. inadequate attention to livestock, poultry, and other combination farming;
6. inadequate annual rate of savings for a healthy growth in the economy, because agriculture does not generate enough, and industry has yet to develop; con sequently agriculture cannot develop further because there is not enough capital to invest, thus resulting in a vicious circle;
7. a great part of the population lives on a subsistence economy that does not participate in the general economic market, and so is not included in the national statistics on which GNP calculations are based: GNP figures for developing countries therefore give only part of the story, in contrast to GNP statistics in advanced countries where they reflect the total economic activity;
8. the phenomenon of rural migration to cities caused by continued disruption of rural balance;
9. the recent introduction of capital-intensive, labour saving technologies that, in most cases, do not satisfy the socio-economic needs or meet the infra-structural situation because capital is scarce and manpower is abundant; and 10. wide economic disparity between the modern and traditional sectors of society. The latter, the members of which live mostly on a subsistence economy, produce raw materials for domestic and urban use or for export. This sector's relationship to the modern sector is similar to that between developing countries and advanced countries, namely one of dependency. Most of the benefits of trade are reinvested in the modern sector, which causes a further increase in the already wide disparity between the rich and the poor.


The term "agricultural residues" is used in a broad sense to include wastes from agriculture and agro-industries. They may consist of unutilized excesses, or of residues from the growing and processing of raw agricultural products such as fruits, vegetables, meat, poultry, fish, milk, grain, and trees. Residues are those end-products of production and consumption that have not been used, recycled, or salvaged. They are the non-product flows of materials and energy whose economic values, at the present level of knowledge, are less than the cost of collection and transformation for use, and they are therefore discarded as wastes. The volume and composition of these residues could be reduced if there were technological means for converting them into some usable product, if the value of the subsequent product were to exceed the costs of conversion, or if it were judged to be sound governmental policy to encourage recovery and reuse.

If residues can be utilized for human benefit, they are no longer wastes but become new resources to augment limited existing resources. Residue utilization is the equivalent of resource utilization. This relationship should receive broad or recognition. Recycling, reprocessing, and utilization of all or a portion of the wastes offer the possibility of bringing such residues into beneficial use, as opposed to the current methods of disposal and relocation. The keys to successful residue utilization are a beneficial Us, an adequate market, suitable technology to process the residue under local conditions, and an overall enterprise that is socially and economically feasible.

The generation of residues from agriculture and agroindustry is a function of many factors. The quantity and quality of the residues will depend upon the type of raw materials, the production processes, the product mix, the production rate, the product output specifications, the prices of inputs and product, the regulations affecting product quality and use, and any constraints imposed upon discharge of residues. The residues generated are materials and energy. The material residues may be liquid, gaseous, or solid or a combination of forms. The principal energy residues are heat and noise.

The fact that residues are the by-products of production and processing after the values in the products have been extracted suggests a rational approach to better utilization of the residues: (a) to increase the value of the residues and/or the products from residue utilization to commercially marketable levels, or (b) to make it profitable for producers to make better Us of the original material, i.e., not to produce as large a quantity of residues or waste.

Efforts are needed to develop technology and institutional arrangements to utilize better the residues from agricultural production. The need is to consider residues as potential resources rather than as undesirable wastes.

Thus, the better use of residues from agricultural production can help accomplish two important objectives: (a) better utilization of existing resources to meet human and animal food needs, and (b) reduction of potential environmental problems caused by such residues.

The selection and/or development of appropriate residue utilization technologies requires careful study. The following factors deserve clod evaluation:

1. the level of economic and technological development in the area of potential utilization;
2. the available physical and human resources;
3. the social change that may be necessary to implement the technology, or that may be caused by the use of the technology;
4. the existing practices and technologies capable of being used;
5. the institutional arrangements to implement the technology and utilize the product of the technology;
6. the available research and development institutes that may help to modify and develop suitable technology, to raise the level of application of the existing technologies, to assist in the production of new products, and to identify the market potential of the resultant product, including export possibilities.

The successful application of residue utilization will require a systematic effort for the selection, modification, transfer, and utilization of technologies for use in a specific location and with specific residues. The ability of local manpower to operate and service the various technological approaches requires careful evaluation. Specific educational programmes may need to be instituted to assure qualified manpower.

Achieving better waste management and residue utilization will depend on the development of the indigenous capacity to generate and operate ecologically and economically viable technologies. The technology for residue utilization has to be applicable to, and integrated with, the actual needs of a country or region. The level of operations, availability of raw materials, market demands, and trained personnel vary from region to region. Adequate research and development must be employed, and the modification of possible technology must be explored to meet the specific needs of an area. Market surveys and studies of the rate of growth in demand for the products of residue utilization also need to be undertaken.

Residue utilization approaches that do not include adequate considerations of the socioeconomic conditions of the specific region or country are less likely to succeed.


The enormity of post-harvest residue generation can be seen from the example of rice. Its annual world production is of the order of 250 million tons. The post-harvest residues generated are (in million tons):

Straw 700 - 750
Husks (or hulls) 70 - 75
Bran 15 - 20

Uses for residues

Rice straw is used as a cattle fodder, for paper and board manufacture, and as a reinforcing material in the preparation of mud plaster. With progressive introduction of high-yielding varieties that give lower straw yields, its total availability may be restricted.

The quality of husk depends upon the type of rice mill. In the huller type of equipment, the husk is obtained in a fine broken state and is always mixed with some bran and broken rice. This is usually used by farmers as cattle feed or as a fuel in the rice mill itself. In the sheller-cum-huller or modern rice mills, the husk does not carry any admixture

The present uses of rice husk are: as fuel in the rice mills for parboiling, in brick kilns, and in households; as a soil conditioner, especially after partial burning; as a bedding material for poultry and livestock; as roughage in animal feed; as a packing material; and as a building material (hollow blocks). An unusual use of the ash left from burned husks is made by washermen who mix it with soda ash to make laundry soap.

Most of the rice bran is currently used as an animal feed. Even in India, which has a large solvent extraction industry, only 40 - 50 per cent of the available bran was extracted in 1975, yielding 90,000 tons of oil. The scattered nature of rice production and the consequent difficulty of bran collection is a constraint, as is the highly unstable nature of bran (fat), which induces the rice miller to sell the material quickly, In India, several rice mills have installed simple and inexpensive bran stabilizers where bran is heated to inactivate lipase, making it possible to store the bran for 30 - 40 days. R ice bran oil has a 3.5 - 9 per cent wax content that is deposited during storage. It is used in the manufacture of polishes and carbon paper.

Most of the rice-bran oil is split and distilled to produce fatty acids and glycerol. Fatty acids are used for making soaps, and in rubber and other industries. The de-oiled bran is exported or used as a cattle and poultry feed.


Rice straw has a fruitful use as a source of pulp and paper. With its diminishing availability as more and more land is planted with high-yielding varieties, greater attention needs to be paid to the utilization of husks and bran. However, some new approaches to rice straw utilization as an animal feed are under investigation in Singapore. These include treatment of straw with alkali and subsequent ensilage, ammoniation, high-pressure treatment, and surface fermentation. The last steps are capital-intensive, but alkali treatment followed by ensilage is considered promising.

First and foremost, the rice mills have to be modernized not only to obtain better yields and higher quality of husk and bran, but also to increase the yield of head rice by reducing the brokers.

A variety of new uses can be found for rice husks. The manufacture of activated carbon and sodium silicate and production of carbon black are possibilities being investigated in India. Both carbon black and silica (white carbon) are used in the manufacture of certain types of tires and tubes. Rice-husk carbon black may be a cheaper substitute.

In Thailand, rice husk combined with coconut fibre has been successfully tested as a filtration medium to produce clean water from rivers. The process has immense scope in the densely populated countries of the region, where potable water does not yet reach every home. In the Philippines, a cyclone burner using rice husks has been designed and is currently under test. Rice is also being used for flue-curing tobacco. Another interesting application for rice husks is in the preparation of molecular sieves, a process currently being investigated in India, as is the manufacture of oxalic acid. In the United States, paddy husk serves as a raw material for furfural, along with maize cobs and cottonseed hulls.

In the manufacture of plywood, finely ground materials such as wheat flour are used as extenders during the Clueing operation. Detailed investigation is needed to see if husks of the desired fineness can be used instead. Some preliminary studies have shown promising results.

Another possibility is the manufacture of silicon carbide, which is being investigated in the United States and India. Rice husk has the desired composition with respect to silica and carbon requirements. Because silica in rice husk is highly reactive, it will require a lower reaction temperature. The production of silicon tetrachloride, required for the manufacture of silicone, is being investigated in the United States.

Rice husk has a caloric value of 5000-6000 BUT/lb and an ash content of about 20 per cent. Experiments in India and the United States show that these characteristics can be exploited in its utilization as a raw material for cement manufacture.

Indian workers have also shown that rice husk can be fruitfully used for the manufacture of fire-proof and water resistant bricks, and that its ash can serve as a component of detergent. The husks can also be used as insulating material and for production of producer gas

There are several uses for rice husks in agriculture. They can be used as a soil builder (in the form of mulch), and for prevention of blast disease. In the United States, levels of up to 250 tons/ha have been applied to soil. They can also be used as a supporting medium for hydroponics.

The residues from other crops can be used for similar purposes.


The situation in India today appears similar to the preindustrial revolution era in the West, but with an essential difference: the existence of a rich and diversified body of scientific knowledge and organized research and development systems that were not available to the West at the time of the industrial revolution. This important asset can contribute enormously to the technological foundation of a rational approach to development. It is not the readoption of the technologies of the pre-colonial period that will restore the rural economic balances, but rather the union of modern research and development systems with the experience and knowledge of the ecological and social environment of the rural society that will solve the problems of technological development.

The technologies of the rural sector are based on empirical knowledge. Part of this knowledge was destroyed during colonial rule. The surviving knowledge that has helped in this long struggle for existence consists of a great amount of useful information about the physical environment and its behaviour. It lacks a scientific base. The technologies based on this knowledge are therefore static and do not have the capacity to interact with rapid technological changes for two reasons: 1. modern industrialized technological solutions have no relevance because they are not related to the rural environment; and 2. the rural sector does not have the economic capacity to accept the solutions, even if they are relevant. Thus, there is a need to integrate indigenous research and development with the body of empirical knowledge possessed by the traditional system.

The modern and traditional sectors in the developing countries have two separate sources of technology, and they tend to drift apart as the modern sector becomes increasingly integrated with the advanced countries. Mere expansion of the modern sector by Western-oriented industrial development cannot be transferred to the rural sector, a fact borne out by the recent experiences of India, where this orientation has made the rich richer and the poor poorer. What is needed is the growth of both sectors in such a way that the gap between the two is closed in a minimum amount of time. Because the traditional sector lacks a scientific base, indigenous research and development can play a pivotal role in closing this gap.

Farming is the largest single human activity in India. Farm wastes are cheap, abundant, and a renewable resource. Their industrial utilization will not only stabilize the rural economy, but will also put an end to the "urban pull." It will increase the purchasing power of the people, which will result not only in investment for improving agriculture, but also for the proper growth of the modern sector. To this end, modern research and development will have to be united with traditional experience to ensure equity and social justice. It will be necessary to:

1. prepare a resources inventory;
2. study the technologies currently being used and examine their empirical foundation;
3. study how these technologies could be used, improved, or adapted to find solutions for meeting basic social demands;
4. define each field of activity, and the type and characteristics of technologies to be used in terms of their functions;
5. design well-defined, long- and short-term research programmes to provide technological solutions;
6. monitor the adequacy of the technologies developed;
7. introduce appropriate modern technologies to set up need-based and resource-based industries that are in harmony with the environment; and
8. build up a socially responsible management and marketing system that will ensure an equitable distribution of wealth.

The concentration of research and development efforts on solving specific problems of development will also allow a more rational approach toward the import of sophisticated technologies.


Apart from some primary processing of agricultural commodities and forest produce, agro-based industries in India are located in distant urban areas where infra-structural facilities are available and close to the urban market. Case studies on mini paper plants and on the production of fatty acids and glycerol from largely unexploited forest tree seeds show that: 1. freight charges contribute substantially to the cost of production; 2. capital-intensive technology provides only marginal gain in the yields of products/returns; 3. labour-intensive technology through dispersal of industries yields higher returns, despite employing larger numbers of persons; and 4. the annual returns/investment ratio is higher in labour-intensive mini-plants compared to that from large plants.

Mini paper plant

Larger paper plants have a 200 - 500 ton-per-day (tpd) capacity. A 250-tpd plant employing 3000 persons requires an investment of $US100 million; 375 - 500 tons of raw material are needed daily; and water consumption is about 75,000 - 100,000 gallons per ton of paper. This places severe constraints on location, resource availability, and environmental control.

A mini paper plant of 5-tpd capacity does not have to depend on distant forest-based raw pulp. It can use agricultural wastes such as straw, grasses, and cotton lint. These waste materials cannot be transported over long distances because they are bulky and widely dispersed. Hence, they are not suitable raw materials for large plants. A 5-tpd plant based on rice straw and cotton lint costs $US1 million, employs 150 persons, and does not have serious problems of raw material availability and effluent disposal. This kind of mini-plant is able to compete with large plants.

Fatty acid and glycerol mini-plants complex

A comparative study was made of three alternative plants processing 40 tpd of minor forest oilseeds to fatty acids and glycerol. The first alternative is based on an actual plant located in an urban area where infrastructure for a sophisticated technology could be used. The second alternative is in the same location, but minus the solvent extraction plant included in the first alternative. The third alternative consists of a complex of ten mini-expellers, five splitting plants, and one fatty-acid distillation and glycerol recovery plant, dispersed over a large area.

Comparative data for the three alternatives examined, on the basis of the following specifications, is given in the ac companying table.
Capacity: 40 tpd oilseeds in all cases.
Raw material mix: karanja seed, 25 tpd; neem seed, 15 tpd; mahua seed, 5 tpd.
By-product cake (non-edible): to be used as a fertilizer.

It is clear that despite the higher value of daily production, alternative 1 appears to be the least economic (returns/ investment ratio only 0.91) while alternative 3 is socially and economically the most desirable. The project in this case will operate in the heart of a rural area, providing direct and indirect benefits to the community as a whole. The returns/investment ratio is also highly favourable 11.94). In addition, it provides the only practical method of using otherwise unutilized minor oilseeds and manpower.

The crucial question from the point of view of social justice is the ownership and distribution of the Rs 10.9 million annual returns. It is logical that the benefits of this wealth-generating activity should accrue to the society as a whole. But what about incentives to the community that has generated this additional wealth? Quite obviously, it must have a share. An answer to these questions will naturally determine the organization and structure of this agroindustrial enterprise. A co-operative type of organization will perhaps be the most suitable one. In addition to wages, the workers can share in the profit. It is assumed that it will be externally financed as a community enterprise.

Total investment
(Rs. million) 1.46 8.38 5.63
Number of persons
employed 91 112 338
Investment per person
employed (Rs) 126,000 75,000 17,000
Value of daily
production (Rs) 92,000 88,700 88,700
Annual returns
(Rs million) 10.4 10.7 10.9
Annual returns/
investment ratio 0.91 1.28 1.94

*Eight rupees (Rs) = approximately US$1.

A part of the income from the enterprise will go to the state exchequer as a tax for money to be used in improving agriculture and irrigation, roads, education, and for other activities. The remaining amount will be distributed and used by the co-operative in any manner that is found most socially useful. For example, the co-operative can set aside part of the money as a reserve for starting a new enterprise, or building a school, etc. Re-investment in other activities will naturally benefit the younger generation.

An additional benefit from such an organization would be that the model will attract the attention of people engaged in other activities, especially farming. Even today, farming is a social activity where neighbours and relatives help each other during peak sowing and harvesting seasons, even though the farm lands are owned by individual households.


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