|Bioconversion of Organic Residues for Rural Communities (UNU, 1979)|
|Analysis of bioconversion systems at the village level|
Approach to bioconversion analysis
Some results and costs from integrated systems
Future development possibilities
Shri A M M Murugappa Chettiar Research Centre, Tharamani, Madras, India
The diversity of residue utilization in rural communities is so great and the amounts of residue so difficult to measure that a complete analysis of bioconversion systems is a difficult task. In such a situation, choosing one method of utilizing organic residues over another has to be based strictly on tradition and intuition rather than on rational procedures, if these can be found. It is therefore necessary to evolve procedures for deciding the best mode of residue utilization. This article attempts to do this in the first part, as shown in Table 1. In the second part, some quantitative comparisons are made based on data obtained in this laboratory, referred to as MCRC. In the third part, some developmental possibilities are indicated for the future. Though an attempt has been made to obtain information from the South and East Asian regions, the background material is based mainly on the Indian experience.
TABLE 1. Analysis of Bioconversion Residues
1. Approach to bioconversion analysis
2. Some results and costs from integrated systems
3. Future developmental possibilities
Barnett's and companion articles in Biogas Technology in the Third World: A Multidisciplinary Review (1) provide an admirable framework for evaluation of alternative decisions in biogas systems. These references should be required reading for decisionmakers in the rural energy area. The present study may be considered complementary because it looks at bioconversion in general. The analysis is restricted to bioconversion for energy, feed, and possibly food.
Table 2 demonstrates the alternative possibilities for using a common residue, i.e., straw. What criteria should be used by rural people to derive the optimum benefit from the straw? As can be seen in the table, the farmer has a number of choices: how does he decide whether to sell that straw in exchange for other goods, digest it for energy, or use it as fuel or feed directly? It is thus necessary to evolve some simple rules to enable him to make a decision. If self-reliance in energy and feed is the goal considered politically desirable, then the man who owns the straw should clearly be steered away from marketing it for alternate uses not leading to energy and feed.
TABLE 2. Various Present and Future Uses of Straw
Straw and similar residues
1. Building material/composites
3. Feed for animals
4. Ensilage and/or storage
6. Any alternate bioconversion (For example, termites, mushrooms)
7. Any alternate marketability (For example, packing materials)
This is, in many ways, the crux of the problem. What are the socio-political and socioeconomic targets for the rural areas? It seems that unless a determined effort is made to propagate self-reliance, the increasing demands of population, industries, and cities will continue to denude the rural areas even of residues, and rural people will be forced to substitute high technology products, such as kerosene, for their basic needs. However, it is true that even for strictly bioconversion processes, the choice is not obvious, nor are the criteria for making the choice. Figure 1 shows various possible ways to use cattle dung and urine. Such schemes can be visualized for other residues. However, even for the same residue the scheme might vary from place to place.
In looking at alternate possibilities for residue bioconversion, two considerations are of the utmost importance: (a) time, and (b) tradition and acceptability. Figure 1 accounts for these by using the width of the arrows for popularity or tradition: the broader the arrow, the greater the usage of the method. In typical marginal communities, anaerobic manure piles are the rule (process B), perhaps because of ignorance about other methods. This method of bioconversion is also the most time-consuming, as shown by the length of the arrow. For other residues, the most acceptable mode might be the most rapid one because of the need for capital generation. Process A is very efficiently practiced in China, but not to a great extent in India. However, it could be made popular in India.
Process C is for feeding the manure directly to algae/fish ponds, a process that is common in Southeast Asia, e.g., the Philippines. It is not widely practiced in India, though it happens in many stagnant bodies of water naturally. Process D is the biogas process, which could become widely acceptable provided that the capital and technology inputs are there. Process E is almost unknown in the rural areas, though it has the great advantage of being quick. This involves drying the dung, pulverizing it, and feeding it in admixture with bran, etc., directly to poultry. The present practice is for village chickens to grub around in dung heaps, because farmers provide very little feed to poultry.
In the case of dung utilization, time is considered a zero-value entity; if the option for the residue were biogas generation (D), followed by A or C on the slurry, the time needed would still be very much shorter than that required for process B. Thus, there is a need to evolve a system, perhaps a judicious mix of all the processes, that will optimize the output to the farmer. This figure is presented to emphasize the need to build in the rate of biomass production or use along with energy usage rate. Quite often developmental efforts do not include the time component. An example of this is the large effort spent on upgrading cellulosic waste. Unless an alternative is available simultaneously, a waste such as bagasse will continue to be burned in huge quantities, regardless of its potential for conversion to fodder and food.
Table 3 presents all the variables that have to be considered in making a decision on a bioconversion process. If the residue is seasonal, then the process should be designed with minimum idle time for any equipment. This is the kind of information that has to be included as an input under item 1. Similarly, collection efficiency and analysis of residue have to be determined. For items 2 and 3, consideration should be given to whether the residue is individually owned and used or is used by the community and also to whether the desired benefit is short-term capital generation so that the village can then have longer-term benefits or whether planning should be for the long run. Usually, in the poorer Indian villages, it seems advisable to sacrifice even efficiency (if necessary) for quick capital generation, because this is what is desperately needed. In any case, it appears that technology, to stay useful in the poorest surroundings, should be highly adaptive, evolutionary, and integrated.
TABLE 3. Considerations in Choosing a Bioconversion Process
|1. Nature of residue||Seasonal/perennial? Collection Efficiency?|
|2. Ownership of residue||Individual/community?|
|3. Desired benefit||Capital/fodder, food/energy? Short or long-term? For one
man or community?
|4. Technology||Inputs - advanced or low availability?|
|5. Capital||Inputs - high or low availability?|
|6. Labour||Skill level? Availability/seasonality?|
|7. Energy||Inputs - high or low availability?|
|9. Delay loop||Time for finished steps of bioconversion|
|10. Other factors||Possibility of employment
Health and environment
Alternate marketability (other than bioconversion)
Items 4 to 8 list the main requirements for capital, energy, land, etc. in terms of input and availability. The inputs that have to be listed in such an analysis are based on proces-specific considerations and availability on region-specific considerations. For example, a process such as yeast culture might involve high energy input in a low energy availability environment and, therefore, be undesirable. Items 9 and 10 are equally important. A process might have to be rejected because the residue is needed urgently for an alternate use; therefore, the time rate of utilization and availability of the end-product become paramount considerations. Also, environmental factors and employment possibilities might dictate the total choice of a bioconversion process.
Thus, a proper analysis of the bioconversion of organic residues needs to encompass all possible factors and combinations. Usually the choice is not as difficult as it appears, because very few residues are available for bioconversion, except in the more prosperous villages. These, however, are a minority. In some areas where MCRC is active, the choice seems to favour a process that will lead to initial capital generation. Once capital is generated, time rate of utilization becomes less important and more elaborate, but more efficient, designs can be put into use.
To show how the factors in Table 3 are applied, the use of a residue, biogas effluent, for three bioconversion processes leading to poultry feed or fodder is discussed next. All three processes have potential application in the rural areas, though perhaps not in the immediate future. In the next section, processes leading to different end-uses, energy and fodder, are considered and compared.
Consider the mass culture of algae, yeast, and photosynthetic bacteria on biogas effluent. Spirulina has been grown by MCRC on such effluent, unfiltered (2 - 5 per cent of the total culture), with an initial boost of 50 per cent by weight in Zarrouk's medium (2). The open-air culture is harvested every other day and dried in solar driers. The skill level needed is high-school-trained workers; other than that, there are no special requirements. The methods, culture ponds, etc., are described in MCRC's Technical Notes (3). The average yield during the months of June to September 1978 was 10 g/m²/day in ponds with a maximum depth of 30 cm. This was a period of unusually heavy monsoon.
Compared to the yeasts, algae cultures, especially the blue-green algae, are very slow yielding. Irgens and Clarke (4) have reported the possibility of yeast culture in anaerobic digester supernatant supplemented with 1 - 2 per cent carbohydrate. The energy and skill requirements are very high, especially in the harvesting cycle. Unless the yeast is used for feeding as a slurry, this process might not, in spite of its higher yields, be adaptable. However, the potential for single-cell protein production at the rural level is high because of the low land requirement (see, for example, Slesser ), high nutrient value, even accounting for nucleic acid content, and availability of substrate.
The situation with photosynthetic bacteria (6) is similar, except that the yield is even higher. At MCRC, work is continuing on cultural photosynthetic bacteria on gobar gas effluent in inexpensive, sealed PVC bags. Harvesting the biomass is difficult, so the slurry must be fed directly. The land requirement for this procedure is low, but the skill, energy, and monitoring demands are very high. The comparison is given as an example of the choices available. The best choice would obviously be for algal cultures. with yeast as a future possibility.
Deciding among widely differing end-products is even more difficult. For example, if the choice is between making compost out of a residue or converting it to energy or to edible biomass for animals or humans, comparison must be made of the benefit of something that is expressed in megajoules versus something that may have an additional value (other than energy) as a protein source. The mere caloric value of a foodstuff is inadequate as a basis for comparison with other materials as far as its benefits are concerned. There is a need for a common yardstick that combines the various uses of organic residues and presents one basis for comparison. MCRC is working on this problem.
Figure 2 shows a system of algal ponds with a biogas system in actual operation in a village. This system has been in operation since September 1978 and is run by local people. Table 4 shows the physical data and some of the costs associated with this system. The technical details are essentially as described in MCRC Notes (3).
TABLE 4. Costs and Other Data for an Integrated Algal Pond System
|Location: Injambakkam Village|
|No.||Item and Description||Cost Rs||Depreciation Rs||Remarks: US$1 = Rs 8.00|
|1.||Digester||878||31.00 (5)||Includes labour, depreciation on materials|
|MCRC design 4 - 5 cattle|
|2.||Geodesic support (MCRC)||322||14.60 (5)||Same as above|
|3.||Gas container||175||88.00 (50)||Depreciation on total|
|Transparent PVC + coconut thatch|
|4.||Piping and burner bought off the shelf||100||10.00 (10)|
|5.||Algal ponds||618||207.00 (50)||Price/m' = 34.34|
|Claylsand bund lined with 1,000 g|
|(HDPE)||Depreciation on materials|
|Exposed area: 3 m² + 6 m² + 9 m²|
|6.||Solar driers||100||40.00 (50)||Price/m² = 33.00|
|(MCRC)||Depreciation on materials|
|7.||Buckets, screens, etc., bought off the|
8. Interest on borrowing 4 per cent/year = Rs 92.00 (4 per cent rates available for poorer sections)
I merest plus depreciation Rs 532.00
Working days/year 300
Average yield 10 g/m² /day or 54 kg/yr
Credits: biogas plus slurry as manure (when not used for algae)
Estimated share of capital towards algae: Rs 6.001kg
Labour: 1/2 man day/day for operation; labour component of capital: 25 per cent
Table 5 shows some actual data from a biogas effluent-fed algal pond growing Spirulina. The second column shows that a medium consisting of one-half Zarrouk's formula (2) plus 2 1 of unfiltered biogas effluent every other day gives satisfactory results. The culture volume was, on average, 150 I; the area exposed was 2 m² /pond; and an initial start of 51 of biogas effluent was added to the culture. Harvesting the culture every other day yielded more than harvesting every day. Occasionally, a bicarbonate boost was given to the ponds to keep up the pH. Small amounts of HPO4² and NO3 were added primarily to the pure synthetic medium culture, but also occasionally to the other cultures.
TABLE 5. Spirulina Growth on Biogas Effluent - Yield and Other Details
Yield dry weight in gas
|Number||Date||Pond PC2 (2m²) - initial dose |
|Pond PC3 |
|Pond PC4 |
1/4 Zarrouk's +
5% v/v biogas
|1||5 Sept.||1978 72||110||102||HCO3, no3 PO4|
|2||7 Sept.||60||45||35||"boost" TO REPLACE|
|3||9 Sept.||50||33||47||carbon uptake by|
|5||13 Sept.||35||50||40||pond PC2, EVERY|
|6||17 Sept.||45||65||-||2nd day after|
|7||19 Sept.||50||90||75||pond PC3, every|
|8||21 Sept.||47||40||65||25th day, plus|
|9||23 Sept.||30||-||_||21 biogas efl, 2nd day after harvest;|
|11||29 Sept.||25||33||45||pond PC4, every|
|12||3 Oct.||20||52||42||21 biogas efl.|
|13||5 Oct.||20||45||35||2nd day after harvest.|
|Yield in gas/m/day||8.36||10.88||9.41|
|Cost of initial
per kg of algae
|Rs 3.05||Rs 1.17||Rs 0.67||Based on 300 days/year|
|Cost of "bost"
per kg of algae
|Rs 20.15||Rs 2.48||Rs 5.98|
The average culture temperatures varied between 27 C at 0800 hours and 34 C at 1600 hours. The lux readings were averaged at 20,000 lux (0800 hours), 80,000 lux (1200 hours), and 16,000 lux (1600 hours). To prevent photo-oxidation, coconut thatch covers were used for the first three days and between 1100 hours and 1500 hours every day. The pH ranged between 9.5 and 10.5.
Based on the data obtained here (work is continuing), some calculations are presented to evaluate and compare different bioconversion modes. As pointed out earlier, this kind of evaluation has to remain subjective until more quantitative yardsticks are evolved,
Consider a family with five cows, and assume one year of operation. Then assume:
Calculation of carbon balance:
5 x 10 x 0.18 x 365 x 0.30
cows kg/cow dry days C/dung
= 788 kg C/yr, entering the system
(Mol. wt. of gas = 24.5, with no correction for normal conditions)
0.067/22.4 x 365 x 50 x 0.8 x (0.65x12+0.30x12)
moles of gas days kg collect C/CH4 C/CO2
= 498 kg C/yr, leaving as biogas 788 - 498 = 290 kg C/yr, leaving in slurry
Based on MCRC's experience, if the slurry is to be fed into algal ponds every other day, approximately 4,0001 of culture ponds are needed. This can be accommodated in ponds of about 14 m² with a depth of about 0.3 m. The yield of algae over 300 days of pond operation can be expected to be 42 kg (at 10 g/m² /day). If two ponds are used, the yield is doubled by feeding each pond alternately.
If carbon comprises 50 per cent of the algal biomass and nitrogen 9 per cent, then C utilization is 17 per cent based on the carbon in the slurry, and nitrogen utilization is about 21 per cent. This is for 150 days of feeding slurry into one pond.
Table 6 shows a projected comparison of five modes of dung use without reference to cost. It must be emphasized that where no bibliographic references are given, the data were obtained or estimated by MCRC. They have to be checked again; an attempt, however, has been made to be conservative.
The first three items in the table are self-explanatory. The fourth and fifth items involve one use of dung as compost. This is to grow Sesbania grandiflora (agathi) trees, highyielding leguminous trees, growing indigenously all over South India. They are used for fodder, fuel, and building wood. Our experience is that 9 to 12 months after planting, the trees grow to 6 m and weigh an average of 16 kg. However, the yield given in the table is yield over unfertilized land. T.M. Paul (13) has demonstrated that barren, rocky land can be used to grow trees. If such land is used, the cultivation of tree crops becomes worthwhile. If land has to be paid for, the cost goes up sharply; in fact, up to 80 per cent of the final value of the crop can be ascribed to land value (12).
Comparison of end-products from bioconversion steps seems to favour a conventional agricultural crop until it is realized that in most villages, land and water are at a premium. However, each situation is different and the analysis here and in Part I may determine the best usage of the residues.
Organized bioconversion of residues seems to be practiced most in the People's Republic of China (14), but it is in its infancy in other less developed countries. However, the possibilities are immense with both conventional and newer processes. A survey of Microbiology Abstracts, Section A (15), revealed at least 25 papers* on processes applicable to rural residues. Thus, a determined effort to work at the rural level on rural residues would yield the best results.
This section indicates some possibilities for bioconversion in the future. Residues from industries situated near rural centres are also listed, because the waste from a medium-sized industry will probably suffice for a whole community. The possibility of generating employment from use of industrial waste should not be ignored. In the Indian context, large industrial undertakings situated near the outskirts of townships and generating usable waste should be encouraged to recycle and re-use the waste instead of resorting to expensive treatment not leading to agricultural products. This would also prevent pollution of the neighbourhood.
Two requirements have to be met for widespread propagation of bioconversion methods: (a) designs for cheap fermenters, and (b) culture or inoculum banks to supply starter cultures. This is similar to the large-scale effort now being launched to supply blue-green algal cultures (16).
If these facilities are provided, and this does not seem too difficult a task, various kinds of residues can be used (Table 7). The table gives only a representative sample and is not meant to be comprehensive.
Locally available grain, millet, and weed residues are added here to re-emphasize the need to make the best use of existing wastes by supplying starter cultures for better ensilage, or by supplying better designs of biogas digesters or fermenters. The available quantity is so vast that commensurate work seems to be called for in order to solve the urgent problem of food, feed, and energy shortages. In many parts of India, harvested straws rot because the harvest and the monsoon are concurrent. Even good drying systems to prevent deterioration (negative bioconversion?) will go a long way to alleviate the problem. Providing every reasonable-sized community a 6 m x 6 m drying platform of hard plastered mud or cement with embedded pipe flanges in a grid would help the villagers dry and preserve their crop residues more effectively. The pipe flanges are used as anchors to fix tent driers of plastic or thatch.
Items 2 and 8 in the table are examples of the variety of process liquors now being underutilized. Paddy steep liquor is available in millions of litres in most rice-producing countries as a result of the parboiling process, and makes nutrients available for fermentation (17). Similar liquors are biogas effluent (4), silk spin liquor (conservatively estimated at about 50 million I per year in one district to Karnataka State alone), coconut water (0.5 x 10(6) tons per year) (18), turmeric" and areca-processing liquors. All these liquors need to be supplemented by a molasses or glucose source for yeast manufacture; they supply N. P. K, and essential vitamins. Items 3 and 9 point out the need for a close look at CO2 as a resource (19). Both biogas as generated and combustion stackgases are thermally valuable as well as being rich sources of CO2 for algal cultures. These gases, being neutrally buoyant, can be transported in balloons to desired locations. Prosopis and forest residues are extremely valuable resources that are now used only for burning. Thayer (20) has grown cytophaga on such material to make fodder. Items 5 and 11 are very effectively used in China (14), and their use should be propagated in other countries.
Regarding item 6 in the table, in India, wherever illicit liquor is brewed, it is done under conditions of very low sterility. Jaggery and acacia bark with some roots and herbs are added to water and sealed in a pot and buried underground. The brew is ready to distill in 10 to 15 days. If the yeast can be induced to multiply under aerobic conditions, it might be a good source of protein. Item 7 refers to the need to develop valuable starch or sucrose residues as cheap substrates for indigenous fermentation. Cotton dust availability in India is 33,000 tons per year (18), and is in a form suitable for enzymatic degradation to glucose, or for 20-day aerobic compost formation. Fish wastes (item 10) can be ensiled in a remarkably simple process (21). The product is a valuable poultry ration and is stable for up to three years. Silkworm cocoons can be dried immediately (to prevent negative bioconversion) and fed directly or ensiled by the same method used for fish wastes.
TABLE 7. Residues Locally Available in Rural Areas and from Proximate Industries
Industrial and Urban Residues
This brief review of future possibilities for rural communities would not be complete without a design for a cheap big-solar fermentation device. This design is not now in use, but might serve to stimulate ideas and improvements.
Figure 3 shows a box-type solar cooker (3) adapted for fermentation. This is made of hollow tiles and plastered with cement with a high coefficient of thermal expansion; e.g., lime/wood ash. The cycle undergone is: Expose to the sun to sterilize, cover to ferment, re-expose for broth concentration. To maintain the healthy growth of aerobic organisms, a compressor driven by a biogas engine, or wind power, or bicycle power, is used to aerate the brew. The tiles provide cellular air spaces as insulation during the sterilization cycle. If it is cloudy, wood-fired heat can be used to sterilize the broth. Though this kind of device cannot mass-produce material, it can be used to provide needed protein for village children.
This article has focused on the factors affecting bioconversion systems at the village level in a typical Indian community. It is fairly obvious that considerations of economy of scale and many other economic criteria that would be important in large-scale industry are irrelevant where the sole goal is to improve protein-calorie intake by a few per cent and to maintain a small, albeit significant, improvement in the quality of life. Bioconversion, in fact all rural technology, should aim only at modest targets. To do this best, the technology must be local, adaptable, and evolutionary. These three qualities do not preclude sophistication of analysis or thought.
An attempt has been made to evolve rational procedures for investment decisions on bioconversion systems at the rural level. Some quantitative comparisons are given based on data from this laboratory. Future possibilities for bioconversion development are also indicated.
1. A. Barnett et al., Biogas Technology in the Third World: A Multi-disciplinary Review. International Development Research Centre, Ottawa, 1978.
2. C. Zarrouk, "Contribution a l'Etude d'Une Cyanophycee Influence de Divers Facteurs Physiques et Chimiques sur la Croissance et la Photosynthese de Spirulina maxima (Setch et Gardner)," Geitler, thesis, Paris, 1966.
3. Shri A M M Murugappa Chettiar Research Centre, Periodical Technical Notes 1 - 4, Tharamani, Madras, India, 1977 - 1978.
4. R.L. Irgens, J.D. Clarke, et al., "Production of Single-Cell Protein by the Cultivation of Yeast in Anaerobic Digester Supernatant with Carbohydrate," J. Appl. Microblol. 2 (4): 231 - 241 (1976).
5. M. Slesser, C. Lewis, and W. Edwardson, "Energy Systems Analysis for Food Policy," Food Policy 2 (2): 123 - 129 (1977).
6. M. Kobayashi, "Utilization and Disposal of Wastes by Photosynthetic Bacteria," in H.G. Schlegel and J. Barnea, leds.), Microbial Energy Conversion, pp. 443 - 453, Pergamon Press, Oxford, 1977.
7. A. Makhijani, Energy and Agriculture in the Third World, p. 121, Ballinger Publishing Co., Cambridge, Massachusetts, 1975.
8. L. Pyle, cf. reference 1, pp. 23 - 29, 1978.
9. A. Makhijani, cf. reference 7, p. 141, 1975.
10. National Academy of Sciences, Methane Generation from Human, Animal, and Agricultural Wastes, NTIS Accession No. PB 276-469, Washington, D.C., 1977.
11. C. Fevrier and B. Seve, Ann. Nutr. Alim. 29: 625 - 650 (1975).
12. C. V. Seshadri et al., Monograph Vol. I I, Energy Plantations - A Case Study for the Coromandel Littoral, Shri A M M Murugappa Chettiar Research Centre, Tharamani, Madras, India, 1978.
13. T.M. Paul, Presentation at the Symposium on Pollution, Environmental Hygiene and Health, Bombay Productivity Council, Bombay, 1977.
14. FAO Soils Bulletin, China: Recycling of Organic Wastes in Agriculture, FAO Bull. No. 40, FAO, Rome, 1977.
15. Microbiology Abstracts, Section A, Industrial and Applied Microbiology, Vols. 1 - 12, 1977.
16. G.S. Venkataraman, All India Co-ordinated Project on Algae, Annual Report 1977 - 78, Division of Microbiology, Indian Agricultural Research Institute, New Delhi, 1978,
17. K. Bose and T.K. Ghose, "Studies on Continuous Fermentation of Indian Cane-Sugar Molasses by Yeast," Process Biochemistry, pp. 23 - 25, February 1977.
18. National Committee on Science and Technology, "Draft Status Report on Utilisation and Recycling of Wastes," Technology Bhavan, New Delhi, 1975.
19. C.V. Seshadri, A Total Energy and Total Materials System Using Alga/ Cultures, Monograph Vol. 1, Shri A M M Murugappa Chettiar Research Centre, Tharamani, Madras, India, 1977.
20. D.W. Thayer et al., "Production of Cattle Feed by the Growth of Bacteria on Mesquite Wood," Develop. Indust. Microbiol. pp. 465 - 474, 1974.
21. Tamil Nadu Fisheries Department, "Fish Ensilage for Animal Feeding," Extension Leaflet No 2, Madras, India, 1978.