Wednesday, February 23, 2011

Greenhouses and Biodigesters: Research

Yay, I hope La Vaquita gets the vote in Dell's Social Innovation Competition!

My technical summary:
Build biodigesters in rural Mexico. Biodigesters take in organic waste and produce both fertilizer and biogas. The biogas can then be burned to heat a greenhouse that protects the biodigester, keeps the biodigester at working temperature during the winter, and can furthermore serve educational purposes for children and eventually grow high-value crops to improve the income and/or nutrition of farmers. Both the biodigester and greenhouse can be made mostly from recycled (thus, low-impact and low-cost) materials.

My Elevator Pitch:
We believe that cow poop is gold. Cow poop: providing income, education, sanitation, and nutrition. Benefiting the environment at low monetary cost, using techniques known for hundreds of years. Biodigesters take cow poop and produce sanitary fertilizer and biogas, which can in turn be burned to heat a greenhouse.

Side Note: There is a flux of terms around this idea. Biogas, biodigester, biogas digester. They all refer to anaerobic decomposition, as compared to composting, which is aerobic decomposition.

Anyway, so the idea (our idea? if I'm in on this) isn't particularly innovative by my standards, which works out because I agree that really, we could focus on implementing proven good ideas, not just coming up with / funding the New Idea of the Year. And there is a clear gap between good ideas and implementation around the world. And we can be innovative in terms of delivery and business model in combination with this technology.
Based on a few internet searches, I would actually say that we have proof (although our own working prototype would be excellent, regardless of local or at MIT) that this concept works. There's even been economics analysis done which raise hope that our intuition is correct and can give us guidance in implementing our own studies.
For instance:
main reasons for failure including: damage to the plastic that holds the gas and waste effluence, general neglect, and a lack of follow‐up and proper system maintenance
Sounds like opportunities for a business model to me.
Oh look! IRRI stands for International Renewable Resources Institute-Mexico. We should talk to them. And they had the same greenhouse idea.

For me to read: all the documentation at <3 It makes me happy whenever I see public documentation.

General reading:
  • Does not specifically address tubular (salchicha) biodigestors, but awesome overview:
By Eric Buysman, GERES Cambodia,
4 pages.
Biogas technology is marginally implemented in cold regions. Most projects are of pilot scale in specific niches, all learning by doing, and it is therefore impossible to extract a best practice. We should however, not look at experiments for biogas alone since there is significant learning from the experiences with greenhouse construction and passive solar housing at high altitude regions.  The results from these experiences could be combined to design an integrated system, which tackles a wide range of problems among poor households about the lack of sanitation, energy poverty, dependence on non-renewable polluting biomass, low income and the short growth season of crops.  An integrated approach is the best solution to tackle poverty from the grass roots level, as it both reduces fuel costs and increases income. Financing biogas a program requires an approach that is aimed at both decreasing the investment barrier (microfinance, subsidies) and on providing the means to increase household income (capacity building and extension programs).
  • High Altitude (below freezing) biodigesters in Bolivia, awesome guide in Spanish:
Biodigestores familiares: Guía de diseño y manual de instalación. 2008.
Biodigestores de polietileno tubular de bajo costo para tropicó, valle, y altiplano
J. Martí Herrero, GTZ-Energía. Bolivia.
80 page manual.
(originally from:

Some studies:
Science Direct search: Biogas Greenhouse

Some miscellaneous: (note key measurements in the studies) (see references at bottom, listed here for people like me on netbooks that multiple site loading times):
Science Direct: Landfill Biogas for Heating Greenhouses and Providing Carbon Dioxide Supplement for Plant Growth Positive Effects of Carbon Dioxide
Slideshare: Alternative Heating Opportunities for Heating Greenhouses
You do not need to remove the CO2 from the gas to burn it, but you should obtain a burner that burns biogas. The CO2 released will encourage plants in the greenhouse to grow faster, so it should be possible to release the exhaust gases into the greenhouse. ... The main problem with burning the gases inside the greenhouse is getting the heat balanced within the building. A burner will release large amounts of heat in one place, so you need a system to circulate this heat to get the whole greenhouse at a uniform warm temperature. A boiler can be used to heat water, which can be pumped around heating pipes. Alternatively, the flue gases can be mixed with a larger quantity of cold air, to get the correct temperature, before it is vented into the greenhouse via air ducts.
 Some videos:
"complete installation of a biodigester in the altiplano (cold climate) of Bolivia"


  1. Hi Nancy,

    Did you start the project?? I am currently running a 150cow farm and im looking for concrete ideas and plans on constructing a greenhouse that can be heated with the bio-gas that the cows are producing.


    1. Hi! No, I did not actually start this project, but the students following me did. Some of the links on this post have concrete plans for making a greenhouse/biodigester setup, and if you give me an email address to contact you I can link you up to some friends doing work in Mexico (who did get around to making a greenhouse+biodigester).
      Sorry for the late reply, I had finals and then I went celebrating the holidays.