In class on Wednesday, February 8, we discussed the Material Flow Economy, or, as our textbook calls it, “the waste stream.”
Here is a visual representation of the waste stream. This can also be called a "cradle-to-grave" model.
Basically, the material flow economy talks about how goods are produced and where they eventually end up (this model began with the Industrial Revolution). In other words, products that consumers buy and use move in a linear pattern from the cradle, or the raw materials used to produce a good, to the grave, where we eventually put that good once we’ve finished using it (basically where the trash or waste goes). So, there are two ends of the spectrum: upstream and downstream. Upstream is where goods are not yet finished; they are still in production. Downstream is the end of the spectrum that collects the waste. The first step of the process begins with extraction of virgin resources. Here, we must drill, mine, and harvest in order to collect all of the raw materials that producers of goods will use to make a product. These virgin resources are natural–they are things like trees, oil, and metals. Then, we move onto the production stage. This is where we use raw materials to make something, such as paper, toys, or electronics. This is the step where we process, refine, and manufacture goods. At this point, the term waste comes into existence. Especially in the production of goods, many industrial wastes never make it into the consumers’ hands, and so the extra “stuff” must go somewhere. Before we talk about the last stage of where waste ends up, let’s first talk about the distribution step. Here, consumers buy the manufactured products. Distribution occurs in stores and markets (on the diagram the store is Wal-Mart). The distribution step incurs the consumption step, in which consumers, people that buy goods, go to the stores to get goods that they will use. But eventually, the things that people use end up in the trash. We no longer use them, and so they become waste. So, what do we do with our trash? Here we hit upon either throwing waste “away” or the three R’s: reduce, reuse, or recycle. First, let’s talk about the “away.” Where does it go? Trash is either buried or burned. If it is buried, it goes to a landfill. Here’s a video about how landfills work.
Basically, there are pipes to collect the leachate so that it doesn’t reach the water table, and there is also a layer of plastic and a layer of clay (which contributes a layer that has low absorption so as not to infiltrate the ground with the liquid of the garbage). Finally, a cap is added to the top, on top of which grass is planted. But there must be a vent to allow the methane gas to escape. The gas is produced since the environment is anaerobic. Unfortunately, this methane gas is much worse for the environment than carbon dioxide (it is a heat-trapping gas).
If trash isn’t buried, then it is burned. Here, trash is brought to an incinerator facility where the volume of trash is greatly reduced, but the mass stays the same (it becomes ash and gas emissions). Here’s a video about how waste-to-energy incinerators work:
Finally, trash can also be recycled. This step would take place right after consumption. The advantage to recycling MSW (municipal solid waste) is that after products are taken to a MRF (materials recovery facility), the materials are brought back to the stage of production. So, by recycling, the entire stage of extracting raw materials is skipped. In a sense, this allows producers to use materials that have already been used, thus eliminating the need to create more impact on the environment by, for example, cutting down more trees. Here’s a video about how a MRF works.
Finally, consumers can also reduce the amount of items that they use, or they can reuse the items that they already have, thus avoiding the need to send waste to either be burned, buried, or recycled.
The basis for the material flow economy diagram is explained in this video about “The Story of Stuff.”