Friday, 9 July 2010

Biogas primer

Since experimenting with solar cooking in NW Zambia in 2004/5, and discovering that - at least for where we were - the sun was only giving reliable daily shine for about 6 months of the year, solar cooking wasn't a 'silver-bullet' energy solution.

Shortly before returning home, I came across discussions about biogas - a flammable mix of Methane and Carbon Dioxide - produced by the bacterial decomposition of organic matter in the absence of Oxygen... so called Anaerobic Digestion.

This has been done all over the world for many years and at many scales. I was more interested in the domestic scale of things and eventually came across the work of Dr. Anand Karve of the Appropriate Rural Technology Institute (ARTI) of Pune, India.  Aware that animal dung was a rich source of methanogenic bacteria, Dr. Karve had questioned 'why settle for using the animal dung after the animal has already taken most of the goodness out of the food? Why not feed our biogas digester with the same food that the animal eats!?'

The result of his research was a domestic scale biogas digester and storage unit that produces large amounts of biogas very quickly - compared to the very large and very slow dung digesters.

For example, a dung digester needs to be big enough to accept, daily: 40kg of dung mixed with 40 liters of water - and retain that for up to 40 days.  The output is a fertiliser slurry.

The ARTI-style digester is being fed up to 1.5kg of sugary and starchy material mixed with just 5 liters of water.  The reaction takes 24-72hrs (depending on temperature) so the whole thing can be a fraction of the size of a dung based system.

As yet, I've not been able to build my own system - partly time, partly money but also the fact that I can't really use the gas as we live in a rented house - I don't think our landlord would like me drilling holes through the wall for a gas pipe!  ;)

However, I am closely following the progress of T.H. Culhane from the NGO Solar Cities.  T.H. is also pioneering the employment of different methanogenic bacteria.  Commonly, the bacteria found in the gut of animals - including you and me - is used but these little chaps work best at body temperature ≈ 37C.  As things get colder they go to 'sleep' and stop producing gas.   In collaboration with Professor Katey Walter Anthony, T.H. is exploring using cold-loving bacteria which are found happily producing biogas even in sub-zero temperatures.

See what these "psychrophiles" can do in the Arctic!

More recently I have been following the experiments of Paula Kahumbu from Kenya.  Check out her blog for more good work.

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