Framing the Investigation
Anaerobic digestion is the process that biodegrades
organic material, like manure and plants, and converts them into methane.
The methane is burned to heat water,
and the steam from the heated water is used to turn the turbines of an electric
generator. This creates electricity to power things like our homes.
The first anaerobic digester was built by a leper colony in Bombay, India
in 1859. The anaerobic technology then moved to England in 1895, when biogas
was
recovered from a sewage system and used to fuel street lamps. In the 1930’s,
people began to recognize anaerobic digestion as a science, and research was
done that led to the discovery of anaerobic bacteria and that led to more research
into the required conditions to grow methane bacteria. Then, in 1978, Cornell
University built the first plug flow digester that was able to digest the manure
from sixty cows! We’ve come a long way since then!
There are several types of materials used to create methane gas. The more common
one is animal manure. This method is most useful if you run a farm. The other
way is to use rotting waste from landfill, and that sort of thing. Both ways
require an anaerobic environment (no oxygen), hence the name anaerobic digester.
When you use manure to make methane, you have several choices of what type of
digester you want to use: a Covered Lagoon, a Complete Mix, or a Plug Flow. Usually
the decision is based on what kind of manure you are dealing with and where you
live, and stuff like that: the amount of solids in the manure, the climate of
the place in which the digester will be, the amount of money you are willing
to invest, and how much time you are willing to commit to the project. The amount
of solids in the manure is usually based upon the animal it came from: cows have
about nine percent solids in their manure, so you would use a complete mix or
a covered lagoon, pig manure is about twelve percent solids, so you would use
a covered lagoon, poultry have about twenty- five percent solids in their manure,
so you would use a plug flow, and horse manure is about twenty percents solids,
so you would use a plug flow. The type of digester also depends on the climate
of the location of the digester. Covered Lagoon digesters are not heated, so
they should be used in warm climates, but Complete Mix and Plug Flow digesters
are heated, so they can be used anywhere. Strangely enough, the cost of the digester
can be another factor in the decision of which digester to use. Covered Lagoons
tend to be the least expensive, but that may be because they are not heated,
making them unsuitable for some colder climates. The Complete Mix and the Plug
Flows are about the same price, because they are both heated. Finally, all of
the digesters need a long time commitment, so you can even out the money.
When you are using rotting wastes to create methane, you get it from a landfill.
They stick a tube down into the landfill, and then bring it back up and quickly
seal it. The tube now has methane in it that the waste in the landfill produced,
which they can burn and create energy from. In some third-world countries,
small villages have their own landfill that they can recover methane from and
burn
to create energy, and they use the energy generated to help the whole village
cook! It’s a very smart, environmentally friendly way of making energy!
Another good reason to use methane generation as your energy source is because
it is environmentally friendly! Sunlight goes through the earth’s atmosphere,
and it hits the ground, and reflects back as heat energy. The heat energy normally
can just escape back through the atmosphere and into space, but if there is gas
there blocking it from leaving, it just stays there. This keeps happening and
happening, and eventually, there gets to be so much heat energy, and it gets
so hot, it starts to change the climate of the earth, and that’s called
global warming. If we didn’t capture the methane released by land fills
and manure, it would go straight into the atmosphere and cause that global warming.
If we capture the gases and use them, then they won’t do that!
The point of the experiment I am trying to do is to find out if fertilizer
affects the process. It could make the methane generate faster, or completely
inhibit
growth. I suspect that it will help the methane generate faster, considering
that when all is said and done in the anaerobic process, the left- over organic
material makes excellent fertilizer, so real fertilizer might help! I hope
to get some results showing actual methane production, but even if no methane
is
produced, it will still be educational because it will show that what I did
didn’t
work!
Methanogenic bacteria.