Today in class, Eva and I learned about biodigesters and how they can be used to create methane in an eco-friendly manner, which can then be used for cooking.
-biodigestor fact sheet
-University of Wisconsin
-simple explanation of what a biodigester is
-explains anaerobic digestion
“A biodigester is like a mechanical stomach. It is fed with organic material, which is broken down (decomposed) by micro-organisms (bacteria) is an oxygen-free (anaerobic) environment to produce a renewable energy called biogas (methane and carbon dioxide) and other material that is mainly used as fertilizer.”
video on how a biodigestor works
-brief history of fuel-related issues and hazards around the world
- two main designs
*the floating canopy (Indian): "consists of a drum, originally made of mild steel but later replaced by fibreglass reinforced plastic (FRP) to overcome the problem of corrosion. The reactor wall and bottom are usually constructed of brick, although reinforced concrete is sometimes used. The gas produced is trapped under a floating cover which rises and falls on a central guide. The pressure of the gas available depends on the weight of the gas holder per unit area and usually varies between 4 to 8 cm of water pressure. The reactor is fed semi-continuously through an inlet pipe, and displaces an equal amount of slurry through an outlet pipe"
*fixed dome (Chinese): "consists of a gas-tight chamber constructed of bricks, stone or poured concrete. Both the top and bottom are hemispherical and are joined together by straight sides. The inside surface is sealed by many thin layers of mortar to make it gas-tight. The inlet pipe is straight and ends at mid-level in the digester. There is an inspection plug at the top of the digester to facilitate cleaning, and the gas outlet pipe exits from the inspection cover.The gas produced during digestion is stored under the dome and displaces some of the digester contents into the effluent chamber, leading to gas pressures in the dome of between 1 and 1.5 m of water. This creates quite high structural forces and is the reason for the hemispherical top and bottom. High-quality materials and expensive human resources are needed to build this kind of digester”
-both designs are flawed/expensive
-full material list of needed supplies for “low cost” biodigester
-outlines methodology for choosing a location and selecting appropriate materials
blog post of ENGR120 students from Spring of 2013
looked at if it would be feasible to create more biodigesters for Sabana Grande
come to the conclusion that it would not be feasible or very beneficial
presentation by ENGR120 students from Spring of 2013
explains the assumptions they made when going through their calculations
demonstrates that with their assumptions, biodigesters break even with propane in the long run
How biodigesters work:
-Takes human/animal waste and encloses it to decompose
methane is released
methane travels upwards
fills bag with gas
gas is routed to be used for cooking fuel
Questions to ask members of the community:
what is your current source of energy for cooking
Is your village/farms spread out over a lot of space?
Do you have farms/livestock?
Are you comfortable cooking with methane from animal and human waste?
What is your current fuel source for cooking?
Is this something you would want to change?
How much time procuring fuel for cooking per day?
Is there space for a biodigester?
Who does the cooking?
Who gathers fuel?
How much money do you spend on fueling cook-stoves/lights?
Follow up--how much of your income go towards fueling your cook-stoves/lights?
How far apart are homes in the village?
Could members of the community share a biodigester?
Pros to having a biodigester:
very environmentally-friendly
can be made using local materials
there will never be a shortage of human/animal waste to use as fuel
Cons to having a biodigester:
Design specifications:
must have two chambers - one for fermentation and one for storing methane
must be durable
must include bacteria to ferment waste in the first chamber
must be large enough to work but small enough to be on a household scale
SAFETY
Our brainstormed prototype: There are two oil drums - one to hold manure and contain the fermentation process and another to store the methane produced and direct it to a cookstove. A flexible rubber inner bag within the drum used for storage will act as a diaphragm and expand and contract in conjunction with methane levels. We’d then pipe this gas into a cookstove for use. It could be buried for more year-round reliability and storage or it could be above ground for a simpler, more immediate solution.There would be some sort of pressure-sensitive valve to control the flow of gas outside of the storage drum. This valve would make the prototype much more safe - by including a stopper, we are ensuring that methane would not leak out of the device and accidentally ignite.
