Waste Not, Want Not Culhane used some of the sustainable ideas he learned to invent something new. He wanted to provide energy in a diff erent way. Culhane says that most of what we call
“kitchen waste,” “toilet waste,” and “garden and yard waste” have value. T ey can be reused. T ey can be a source of clean fuel and fertilizer. He calls his invention a biodigester. T e
bio stands for “living.” T e digester part tells you it “digests.” T e invention uses the same microbes that people and animals have in their guts to break materials down. So, you can put used cooking oil, food scraps, and grass clippings into the biodigester. People in rural areas can add manure from cattle and sheep.
How it Works Inside the biodigester, the microbes break down what you put in it. T ey do this in the same way your stomach breaks down food. Over time, the container fi lls up with biogas. Biogas is what forms when living things break down. It’s a combination of methane, carbon dioxide, and sulfur gas. Burning biogas releases energy. So it can
be used as a fuel. It can be used to heat a room and cook. It can also be used in a gas engine to change the energy into electricity. In a system, the amount of energy put in
relates to how much energy comes out. So in a biodigester, the amount of energy released depends on how much food you put in. Culhane uses a plastic bucket to measure how much energy in food scraps and used oil goes into a biodigester. One full bucket of food scraps a day releases enough gas to light two small rooms for an evening or cook two meals.
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Culhane’s Biodigester
T.H. Culhane invented a device he calls a biodigester to create energy from waste. Here’s how it works:
Food scraps, manure, and organic materials are dumped
into the biodigester.
Microbes break down the contents of the biodigester. Biogas moves out
when other materials are put in.
No More Garbage Cans Culhane tested diff erent materials. He found out that freshly cut grass clippings produce four times more biogas than the same amount of dried cow manure. Culhane has designed the biodigesters in
diff erent styles and sizes. Some are just large holes in the ground lined with concrete. Others are big plastic containers. Yet, they all work in the same way. One
pipe is used for putting organic material inside. A second pipe carries the biogas to be stored. A third pipe is used to drain off the liquid fertilizer that forms.
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