Dear Ajuyah,

Greetings from Nepal,

Asifo Ajuyah asked:
>Your paper on Community Latrine-cum-biogas plant in
>Nepal is a demonstration of the practicality of an Integrated Biosystem in
>a community based situation. However, in-addition to the points raised by
>Jacky the following issues might require further clarifications:-
>
>Theoretical concepts.
>(a) Karki what do you think about the C:N ratio in human excreta as sole
>digester input?. I will presume that it would be too low to sustain the
>biodigester (C:N ratio of 15-30), in fact that is why in China rice straw
>is usually introduced into latrine based biodigester, similarly in Nepal it
>has been reported that latrine based biodigester in the Zoo is fed elephant
>dung.

You have brought about very important question on the theoretical concepts about the C:N ratio of human excreta as raw material to run the biodigester. 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. With this concept, in one of our experiments conducted at Machan Wildlife Resort in Nepal, we had used elephant dung (C:N ratio around 40) in conjunction with human waste to maintain desired C:N ratio.

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.

Best regards

Amrit & Upendra