When I talk about Poo Power! and I mention that one of the functional uses of the energy is to light public parks, some automatically assume that light means electricity. Remember, burning gas can also create light. Just think of a campfire, or those old camping gas lamps. So, what is biogas then?
Let’s back up. First of all, bioenergy is the generic term we use to describe renewable energy created from biological sources, or ‘biomass’ - this may include wood, straw, manure, sugarcane and many other by-products from a variety of agricultural processes. The terms bioenergy and biofuel get used interchangeably and this is a common error. Biofuel is fuel derived from those biological sources and in most cases comes in liquid form. Bioenergy’s public opinion gets pulled down by biofuel as it gets caught up in the global food crisis debate, in that do you grow crops for fuel or for food?
Biogas, on the other hand, is methane produced by the breakdown of biodegradable materials such as biomass, manure, sewage, municipal waste, green waste, plant material and crops. This process occurs in the absence of oxygen, 'anaerobic', with micro-organisms doing all the hard work. (We’ll discuss the anaerobic digestion process another time.)
Biogas is a mixture of 60% methane (CH4), 40% carbon dioxide (CO2) and small amounts of other contaminant gases such as hydrogen sulphide (H2S). The exact composition of biogas depends on what is being ‘digested’. Biogas can be burned to provide heat, lighting or both and provides a source of many families to cook their food in developing countries like India. Alternatively, biogas can be 'upgraded' to pure methane, often called biomethane, by removing the unwanted gases and injected into the gas grid or used as a transport fuel. However it takes a lot of energy to compress biogas and therefore energy is usually just wasted. So Poo Power! is keeping it simple for optimal environmental benefit.
Actually, when you think about it, the dog poo we collect in plastic bags are like little biogas reactions in landfill. All Poo Power! is doing is collecting the dog waste en masse and then putting the biogas to a good use.
So when you next hear or read about biogas, remember that all bioenergy is not the same - like all thumbs are fingers but not all fingers are thumbs :)
What to learn more? If you are a student why not ask your science teacher, or if you’re like me I found this link very useful: “The Beginners Guide to Biogas” from the University of Adelaide.
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