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Malee Sundhagul and Poonsook Atthasampunna Bangkok Microbiological Resources Centre (MIRCEN), Thailand Institute of Scientific and Technological Research, Bangkok, Thailand
Thailand, like many other developing countries in South-East Asia, is an agricultural country and, as such, produces several hundred million tons of agricultural products annually. Of this vast amount of vegetables, fruits, fish, meat, and other raw materials used for various kinds of edible and agroindustrial products, some millions of tons are wasted each year. These waste problems become pollutants causing increasing environmental problems. In the ASEAN region alone, for instance, it has been estimated that 30 million tons of rice grain are produced each year. This is accompanied by 140 million tons of straw, 13 million tons of husks, and 2 million tons of bran.
Considering similarly large quantities of other commodities, such as cassava, maize, and sugar cane, tremendous resources of organic raw materials are potentially available for conversion into useful products - the common "F" products: food, fuel, fertilizer, and fibre. Among many means of converting these waste materials - mechanical, chemical, and biological - bioconversion (particularly microbiological) seems to be the most suitable for Thailand, and probably for other tropical developing countries as well.
The vast reservoir of genetic resources of micro-organisms is increasingly being tapped and harnessed for its potential for the detoxification of wastes, the purification of polluted waste effluents, the traditional fermentation of foods and feeds, the production of vitamins and vaccines, the microbial fixation of nitrogen, and the production of biogas as fuel from manure.
The present paper describes the status of bioconversion of organic residues, with particular emphasis on carbohydrate residues.
Sources of Carbohydrate Residues
For the purpose of this discussion, it is proposed to categorize carbohydrate residues into three types: cellulosic, starchy, and sugary. In practice, cellulosic residues are mainly lignocellulosic and sometimes include starchy and/or sugary components. The following are major waste materials under each of these categories with high potential for bioconversion:
Current Traditional Practices
Industries in Thailand have increasingly been recovering residues and wastes from raw materials and plant waste material as by-products in an attempt to reduce pollution problems as well as to minimize production costs for major food items. Cassava residues from starch factories have been recovered for animal feed, and fermentation broth from monosodium glutamate (MSG) factories is used as flavouring for sauces. However, here we will discuss only those methods currently practiced at the rural level with potential application in other areas.
In Thailand, as in other agricultural countries, cellulose is the most abundant organic waste. Consisting chemically of long chains of glucose, it is easily hydrolysed by cellulase enzymes normally produced by bacteria in ruminants. Therefore, one of the most common uses of cellulosic wastes has been as animal feed.
Non-cellulosic carbohydrate residues, such as starch in cassava and sugar-containing residues (molasses), are generally used as feeds for non-ruminants, i.e., pigs and poultry. Broken rice rejected in the milling process, barley, maize, and cassava meal are commonly used as feeds in Thailand. The use of these residues may be considered a form of bioconversion in common practice throughout the world.
Where cellulosic materials have high lignin components, digestion by animals is minimal. In such cases, a small amount of fermentable carbohydrates such as corn meal or molasses is added to produce silage, thus ensuring rapid fermentation. Silage making normally serves as one of the effective means of conserving high-moisture products for animal feed. Corn (maize) silage is most common in Thailand, and cassava is being used increasingly.
Many crop residues are deficient in protein and minerals. It is therefore not uncommon for farmers to add products such as urea and minerals at the time of ensiling.
Fermentation of carbohydrate residues for human consumption is negligible in Thailand. Small amounts of fermentable carbohydrates are sometimes used as adjuncts to ensure rapid fermentation of other easily perishable protein food, such as pork (fermented sour pork), fish (fermented sweet fish, or pla chao), etc.
Biogas production in Thailand has not received adequate attention. Recently, some attempts have been made to promote this type of bioconversion.
Current Research and Development Activities
There has been increasing interest in the productive utilization of agricultural and agro-industrial residues throughout the world.
International. Recently, the US National Academy of Sciences convened a panel of experts from different parts of the world with the objective of producing a document on the current status of utilization of organic waste materials to produce foods, fuel, and fertilizer. In December 1979, UNEP convened a meeting of policy makers and administrators on the subject of waste utilization as a followup of the previous consultative meeting of experts on this subject.
Regional. An ASEAN regional co-operative project has recently been launched by the ASEAN Subcommittee on Protein aimed at better utilization of food crop wastes. The emphases are on converting food waste into acceptable food, followed by making them suitable for animal feed, and as potential alternative sources of energy.
National. Several research and development programmes and projects are being carried out by universities and research institutions in Thailand. Those specifically involving carbohydrate raw materials are as follows:
In applying knowledge of converting residues into useful by-products, several factors must be taken into consideration in order to ensure successful implementation. The four major factors are technical, economic, socio-cultural, and, finally, political - all, in most cases, interrelated.
Biological conversion or bioconversion of carbohydrate residues in Thailand mainly involves traditional fermentation processes that rely on natural inoculation of successive fermentation using part of a previous batch as the inoculum for the following batch. At a more sophisticated level of fermentation technology, pure inoculum is normally used. Fermentation technology has long been used to preserve easily perishable food materials and to produce a variety of foods and feeds.
To help strengthen the efforts to promote conservation, distribution (preservation), and environmentally sound management of available natural resources in Thailand and other South-East Asian countries, the Government of Thailand has established the Bangkok MIRCEN, which serves as a local centre for the conservation of microorganisms of economic and environmental significance, and for disseminating information relating to fermentation technology, particularly in the areas of food/feed fermentation and waste recycling.
At present, several technologies for converting carbohydrate residues into useful and value-added byproducts are known throughout the world and within the South-East Asian region. For village-scale technology, experience in Thailand reveals that those available now are adequate. The problem is how to create awareness among technologists and how to effectively transfer those technologies to the grassroots level for implementation. Information exchange, effective promotion, and support - particularly from the government - are considered most important.
In general, the adoption and implementation of bioconversion technology will depend largely upon the economic feasibility of integrating these practices into existing agricultural and agro-industrial residue management schemes. In most cases of rural agricultural and agro-industrial operations, collection of residues in a large enough quantity to be economical to process is a major problem. Transportation adds to raw material costs and leads to problems such as need for adequate storage facilities and deterioration in quality. In many instances, transportation facilities are not adequate.
Where recovery or treatment of residues is necessary largely for environmental reasons, potential economic benefit is rarely realized. In such cases, it is anticipated that at least operating costs can be recovered.
A survey was conducted in Thailand to identify socio-economic issues surrounding the practical feasibility of wide-scale promotion of biogas generation. It was found that most farmers were generally aware of the technology, but economics were the primary concern. They were found to be understandably conservative regarding additional capital expenditure. This attitude is also true among industrial entrepreneurs in the country, with the exception of those operating joint ventures with foreign counterparts.
The adaptation of new technologies to existing socio-cultural and economic systems has always been a complex process. The issues are more serious among villagers in rural areas with little or no education. In a survey to promote biogas generation from combined human and animal wastes, several people viewed the approach and proposed technology as unethical. Several others interviewed would not utilize biogas generated from pig manure, and many would not handle the manure.
Political decisions and government measures are sometimes necessary in promoting the adoption and implementation of waste utilization schemes. This is particularly true in the area of waste treatment to solve pollution problems where economic benefits are not the primary objective.
Maximum and proper utilization of farm and agro-industrial wastes will inevitably result in better environmental management and additional income-generating sources, thus improving the quality of life for the rural poor. Improvement in agricultural productivity by using spent compost in the soil, thereby minimizing reliance on expensive inorganic fertilizers, will increase availability of foods and feeds, etc.
Support and encouragement by the policy makers, planners, educators, and implementors are necessary to help realize the above-mentioned goals.
In the coming decades, Thailand, as well as many other developing countries in the region with an abundant supply of agricultural raw materials, will rely significantly on beneficial microbes in their bioconversion efforts to meet the crises precipitated in food, fuel, environmental and other socioeconomic sectors.