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close this bookBioconversion of Organic Residues for Rural Communities (UNU, 1979)
close this folderIndian experience with treated straw as feed
View the document(introduction...)
View the documentIntroduction
View the documentExperience with straw treatment
View the documentField testing and demonstration of straw treatment
View the documentGeneral considerations
View the documentSummary
View the documentAnnex 1. The energy efficiency of the two-stage, feed-fuel processing of straw in indian villages
View the documentAnnex 2. Method of calculating the value presented in table 2 for the efficiency of naoh energy usage
View the documentAnnex 3. Recommendations to farmers on the treatment of straw
View the documentAnnex 4. Calculated efficiency of milk production by straw-fed village buffaloes
View the documentReferences
View the documentDiscussion summary

Annex 1. The energy efficiency of the two-stage, feed-fuel processing of straw in indian villages

Table 3 shows the calculation of energy efficiency for different methods of using dung as fuel. The following factors are taken into consideration.

TABLE 3

  Traditional open fire-place Closed fireplace with chimney Biogas production
Energy content (MJ) of:      
Original straw 100 100 100
Resulting animal products and services 4.6 4.6 4.6
Resulting dung 55 55 55
Gas produced from dung     15.4
Useful energy obtained from dung (MJ) 5.5 11.0 9.2
Deduction for energy equivalent of nitrogen lost (MJ) - 1.5 - 1.5  
Total useful energy recovered from straw 8 14.1 13.8
Efficiency of processing (%) 8.6 14.1 13.8

1. 6.9 kg straw containing 90 per cent dry matter and having a rate of combustion of 16 MJ/kg dry matter contains 100 MJ combustible energy. This amount of straw is approximately the daily consumption by an adult bovine.

2. The efficiency of animal production on a typical straw diet is calculated (see Annex 4) to be 4.6 per cent. This value is for the diet as a whole, the value of the straw component is probably slightly less.

3. 18.3 kg of dung containing 20 per cent dry matter and having a rate of combustion of 15 MJ/kg dry matter (the digestibility of straw energy averages 45 per cent) = 55 MJ.

4. 18.3 kg wet dung x 37 I biogas/kg wet dung x 0.61 CH4/l biogas x 0.038 MJ/l CH4 = 15.4 MJ.

5. The efficiency of burning dung in an open fireplace is estimated to be 10 per cent, in a close fireplace with chimney, 20 per cent, and in a gas burner, 60 per cent (2).

6. Assuming that 50 per cent of the nitrogen contained in straw is recovered in dung, the manufacturing energy value of this nitrogen is:



7. Total useful energy = energy contained in animal products and services + useful heat energy - deduction for energy equivalent of nitrogen lost.

8. Efficiency of processing = (total useful energy obtained x 100) / (energy content of original straw)