Amrit & Upendra,

You answered:
>According to literature, it is said that the optimum C:N ratio
>for biodigester is around 30, while human faeces has a C:N ratio around 10.
>.....(cut).....
>On the other hand, few years back when I visited a latrine-cum-biodigester
>installed at Cox Bazar beach of Bangladesh, I found that the biodigester
>had been working excellently with human excreta only. Our project at
>Pathari was inspired by the experience of Bangladesh. Similarly, one
>community latrine plant installed few years ago at Dharan of Sunsari
>district in Nepal has been producing biogas only with human excreta.
>
>In our experiment at Pathari, intially we used cattle dung to produce
>biogas. Then, once the gas was produced, the latrine was connected with the
>biodigester and animal dung was not used any more. Presently, it is
>producing gas only with human excreta as raw materials.
>
>All these examples practically show that human excrea which has low C:N
>ratio can be used to produce biogas without addition of cellulotic
>substate, for example rice straw, which is used in conjuction with latrine
>waste in China to feed biodigester.
>
>It seems necessary to explore the cause for which an  appropriate R &  D is
>needed to be conducted in this subject.
 

I think the C:N ratio depends so much in diet people used. The literature "the C:N ratio in human excreta is around 10" can lead a wrong thinkings. If you look at meals of Vietnamese farmers you can notice a great difference in comparison with meals from Nepal people. The difference should be greater between wealth categories.

Do you think an appropriate R&D is must based on what people eat?
What was the C:N ratio of the diet people in Pathari ate?

Regards
Bui Xuan An
UAF, Ho Chi Minh City
Vietnam