Dear Juergen,
Thank you for sharing these presentation from TED. Let me quickly comment on the two.

The biocenters built from Umanda Trust are very helpful to ease the devastating sanitation situation in the slums of Nairobi. However I would like to caution the prospects of this technology. From my own experience with Umande Trust it is very difficult to treat and safely dispose the waste from the biodigesters. First of all there is very little space in the slums to fit a treatment system like baffle reactors or constructed wetlands. For this reason they have situation the biodigester underneath the toilets. Some of the toilet centers are run without any flushing water, so the effluent of the biodigester is very concentrated and requires treatment. I am not sure how they handle it in most cases, but I have seen from pictures that they desludge the biodigsters regularly with a gulper (from expansion chamber). It would be very interesting to get the operational costs per biocenter in order to see how much they spend on waste disposal.

Using the Gulper von Sustainable sanitation auf Flickr

The second video is full of new ideas. Great. I like the tube digester and its simplicity. Not sure if they get the material from local producers in Kenya. Would be great to learn more about them. Anybody knows Dominic Wanjihia of Biogas International Ltd? In case you use this system with human waste it is definitely not ok to directly apply it to the field without any precautions. There will be certainly pathogens remaining in the effluent, so application should be done for certain crops only e.g. fruit trees, timber trees.

Best regards,
Christian

Two talks on Biogas projects in (Kenya's capital) Nairobi, given at the recent TED Talent Search in Nairobi:

Josiah Omotto of Umande Trust

src: talentsearch.ted.com/video/Josiah-Omotto...ng-biogas;TEDNairobi

Dominic Wanjihia of Biogas International Ltd

src: talentsearch.ted.com/video/Dominic-Wanji...-biogas-t;TEDNairobi

Great to see Biogas having such an exposure these days (and it's not a Chinese thing this time around . Some of Dominic's works have also been featured on AfriGadget, btw: www.afrigadget.com/2010/06/09/solving-th...s-digester-problems/ and he does not only work in Biogas (e.g. the milk cooler ). Good stuff!