Biogas generation is something I have been interested in for a long time. If you talk about makeing methane, you hear a lot of flatulence jokes. To be fair, the procedures for making usable biogas, and the procedures for making your friends and family uncomfortable in small rooms is similar.
In both cases naturally occurring bacteria anaerobically convert nitrogen and carbon to Methane (CH4). Methane is the primary component of LNG or Liquid Natural Gas (about 87%) and is an attractive fuel since it is abundant, easy to manufacture and produces little carbon dioxide per unit of heat.
What is Biogas (Methane)
Methane is odorless when pure. The swamp gas smell people blame the family dog for comes from sulfur compounds that taint the methane.
In many locations (primarily India) Methane is produced locally and piped internally into homes. This is used for domestic cooking and lighting. It is very similar to propane in use. Additionally, it can be adapted for use in internal combustion engines just like propane.
How to Produce Methane
Producing methane is pretty straightforward. You introduce slurry of manure, plant material and water into a closed container with a fitting to allow the gas to escape. Once the natural bacteria from the manure use all the oxygen in the container, other bacteria convert the slurry into fertilizer, methane, and waste heat. The perfect ration of bacteria feed is 30/1 or 30 parts carbon to 1 part nitrogen.
A simple internet search of DIY methane, or similar keywords will show many different methods of methane production. However, my problem has been a lack of material concerning sources of manure other than the common pig and cow manure. I don’t have either animal. What I have are rabbits. Rabbits, due to their cage setups, would be perfect manure output devices. It would not be hard to create a system where their waste products flow directly into a batch type methane generator.
Rabbit Droppings are Low in Carbon
The problem is, I cannot find anyone who has tried to make rabbit manure methane. I know that rabbits are producers of high nitrogen/low carbon manure, so I am not sure they are optimum producers.
I was taking a Agro-terrorism response class taught by some LSU professors. On a break I thought I would try to get some free advice. So I asked them what they thought. Their advice was worth exactly what I paid for it. They said “why don’t you just try it an see”.
They weren’t being smart, just letting me know that there isn’t any good documentation on the subject of using rabbits for methane. If I wanted to know then I should experiment.
I Wanted to Know, So I had to Experiment
I decided to perform a simple jr high type science experiment to see if it was worth investing my time and resources into development of a better system.
In a very unscientific manner took two 20oz soda bottles and filled one with a simple slurry of rabbit manure and water, and the other with rabbit manure, water, and some bedding straw for added carbon. I then covered both bottle openings with small balloons both as an airlock, and to collect the methane.
Next, I took the bottles upstairs to a heated location, and placed them in a plastic bin to collect any leakage (and to hide the bottles of poo from the wife)…
4 Days later, the balloon on the manure/straw mix was standing up and slightly inflated. The balloon on the other bottle was flaccid. Two days later the experiment failed from a scientific standpoint, as both bottles pressurized enough to cause both balloons to fail.
I do not have scientific proof that the gas produced was methane; however, it is likely that it contained some amount.
I can either devise a better controlled experiment, or I can build a small digester. I will think about this a little more and most likely make a small 5 gallon digester later in the summer after the bees and garden projects are better developed.
Results of the Project: