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Some results and costs from integrated systems

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
      (per cent/yr)  
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 m + 6 m + 9 m      
6. Solar driers 100 40.00 (50) Price/m = 33.00
  (MCRC)     Depreciation on materials
7. Buckets, screens, etc., bought off the      
  shelf 50 50.00 (100)  
  Totals 2,243 440,60  

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/m /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 m /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 HPO4 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 (2m) - initial dose
full Zarrouk's
Pond PC3
initial dose
1/2 Zarrouk's+
5% v/v
Pond PC4
-initial dose
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
4 11 Sept. 20 45 52 algae:
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;
10 27 Sept. 28 25 27  
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.
  Total 502 693 565  
Yield in gas/m/day 8.36 10.88 9.41  
Cost of initial chemicals

per kg of algae

Rs 3.05 Rs 1.17 Rs 0.67 Based on 300 days/year
Cost of "bost" chemicals

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:

  1. 80 per cent collection efficiency (7),
  2. 10 kg wet dung/day of 18 per cent dry solids (8),
  3. carbon in dung= 30 per cent by weight of dry solids C/N ratio = 18 (8), and
  4. gas yield of 0.067 m /kg wet dung of 65 per cent CH4, 30 per cent CO2 (8), and the remainder H2 O.

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 m 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/m /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.

Future development possibilities

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

Rural Residues

  1. Grain, millet residues, aquatic weeds, etc.
  2. Paddy steep liquor, biogas effluent, other processing liquors
  3. CO: from biogas
  4. Prosopis, etc., forest residues
  5. Dung, faecal matter
  6. Illicit liquor process adaptation

Industrial and Urban Residues

  1. Carbohydrate residues: sago (cassava waste, molasses, spent wash, cotton dust)
  2. Paddy steep liquor, silk spin liquor, coconut water, areca, turmeric liquors, etc.
  3. CO: from thermal, cement, and fertilizer plants
  4. Fish wastes, silk worm cocoons
  5. Sewage sludge

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.

Figure. 3. Box-type Solar Cooker Adapted for Fermentation


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.

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