[Digestion] Dry fermentation in developing countries

Voegeli, Yvonne Yvonne.Voegeli at eawag.ch
Fri Oct 29 02:06:59 PDT 2010

Dear all,

Thank you very much for your feedback and ideas. We will have to think more about David's' suggestion using two flame traps.

Ken is right; I should have given a bit more details on the project. I have to admit that we are at the very beginning... The project is located in Kumasi, Ghana, and our local research partner is the KNUST University of Science and Technology. The pilot plant shall be located at the university campus and the feeding material will consist of organic household waste or food waste from restaurants. In a first step, two Swiss students will work on the project for 6 months (start in December), spending 4 months on site. Their task is to identify the suitable material, that's why I can't give you the details on what exactly is available. At first, I was also thinking about a shipping container (what about corrosion?), but cement materials are also available as well as skilled workers. We will have to compare the different options and costs.

On principle, the idea is that such a plant would be operated by the municipality or a private contractor (not by farmers), as our focus is on municipal solid waste. There are still many open questions, but my biggest concern was the security - if it is possible at all to construct a simple digester which is safe...

I think the students might contact some of you directly for further questions later on.
Thank you,

From: digestion-bounces at lists.bioenergylists.org [mailto:digestion-bounces at lists.bioenergylists.org] On Behalf Of Ken Calvert
Sent: Freitag, 29. Oktober 2010 09:48
To: For Discussion of Anaerobic Digestion
Subject: Re: [Digestion] Dry fermentation in developing countries

  Yvonne Hi!  When you say developing countries, what sort of construction materials are you thinking of?   Would old 20 tonne shipping containers be available?
Are cement materias and  tradesmen skilled in cement plaster work  readily available?   What about  PVC tarpaulin cloth?  Are there trucks on the roads that have waterproof covers  that can be strapped down  over a load?  What is the local soil and terrain?   Is it possible to dig say 2-3 metres deep in the soil and get a  smooth surface, or is the terrain too soft and sandy to  hold to the shape of a cistern or trench dug in the soil?   Is it too rocky to allow any sort of digging at all?  If you can home in a little more on the country side  and  local skills available  I can make several different suggestions.  Sincerely,  Ken Calvert.  www.coffee.20m.com<http://www.coffee.20m.com>

----- Original Message -----
From: Voegeli, Yvonne<mailto:Yvonne.Voegeli at eawag.ch>
To: digestion at lists.bioenergylists.org<mailto:digestion at lists.bioenergylists.org>
Sent: Thursday, October 28, 2010 9:53 PM
Subject: [Digestion] Dry fermentation in developing countries

Dear all,

I like to start a new discussion on a different topic, namely the dry-fermentation process (discontinuous) similar to the digesters developed by the companies Bekon or Bioferm in Germany. The organic waste is filled batch-wise into simple garage-like digesters for about 30-40 days.

Experts report that this process has a high potential for application in developing countries as it has the simplest design and the solid waste digesters are the least expensive ones. Also, substrates that lead to operating problems during wet fermentation due to their structure or the proportion of impurities they contain can still be processed using dry fermentation methods. However, up to date, there is no experience with this technology in developing countries. Therefore, our idea is to develop a dry-fermentation biogas plant adapted to the situation in developing countries using locally available material.

After visiting a Bekon biogas plant in Switzerland, I'm especially concerned regarding the opening of the digester for emptying and refilling. Before opening the door, the digester has to be vented in order to avoid a gas-air-mixture which is explosive. This installation seems to me rather complicated.

- Is anybody of you familiar with discontinuous dry-fermentation systems and has an idea how the security can be assured in a developing country context? Is it possible to install a simpler venting system?
- Likewise, when removing the drum from a floating-drum digester for emptying, how is ensured that at no time an explosive gas-air-mixture occurs?

Thanks for your ideas,
Yvonne Vögeli
Eawag / Sandec
Überlandstrasse 133
P.O. Box 611
8600 Dübendorf
Phone: +41 (0)44 823 54 20
Fax: +41 (0)44 823 53 99
yvonne.voegeli at eawag.ch

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