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Long time readers may be aware that my father, Ron Danner, is an emeritus professor of Chemical Engineering at Penn State University. This is the second of two columns that we are co-authoring, both of which are pertinent to issues right here in the Southern Part of Heaven. Last week we addressed the choice between paper and plastic bags. This week we provide a review of single-stream recycling.

Aside from being environmentally conscious, municipalities have financial incentives to implement recycling programs. Glass, paper and plastic that residents throw in the garbage must be landfilled. If they are recycled, they can be sold. The three most common approaches to recycling are listed below.

  • Single-stream: Put all recyclables into one bin.
  • Dual-stream: Put paper products in one bin and all other recyclables in another.
  • Source-separated: Divide recycling into many different bins based on material type such as paper, aluminum, clear glass, and brown glass.

In order to select from among these options, a municipality needs to consider all of the steps in the recycling process.

  • The first step involves considering what behaviors can be expected from residents. As you require more separation at the home level, you need more recycling-focused residents. As the amount of separation required is reduced, residents tend to increase the amount of material that they recycle, which in turn reduces the amount that goes to the landfill.
  • The next step involves the collection of materials. The trucks that collect recycled materials must have the same number of compartments as the number of distinct bins at the residence. Multi-compartment trucks are more expensive than the single compartment trucks that can be used in a single-stream recycling approach.
  • The third step is the separation of the materials at the recycling facility but automated machinery. The goal of the recycling facility is to separate everything back out into distinct categories. This task is obviously easier to accomplish if the resident performs more separation.
  • The final step is the disposition of the separated materials. Here, economics plays an important role. The amount paid for a ton of recycled material depends upon the quality of the product. The higher the level of contamination – paper mixed in with glass, or type 1 plastic mixed in with type 2 plastic – the lower the price.

A single-stream recycling facility is essentially a series of conveyor belts. Here is a typical setup.

single stream recycling pic 1

Materials from the trucks are dumped on to the first belt and workers extract the materials that are not acceptable, such as batteries or fluorescent light bulbs, by hand. This belt leads to a separator system that drops out the heavier materials such as cans and bottles and leaves the paper, cardboard, boxes, and the like. Each of these streams are directed to further conveyer belts which separate materials using puffs of air to knock off lighter materials such as plastic bottles and magnets to separate metals. Optical sorting technologies are used to identify different plastics and separate them again using puffs of air. The sorting equipment looks like this.  Two of the biggest problems in the overall process are plastic bags, which tend to wrap around the equipment, and glass, which tends to break and contaminate the final products. Therefore, if you ask residents to perform more sorting at home, the products from your recycling plant will be more uniform and fetch a higher price. Unfortunately, if you take this route, residents will recycle less material reducing the volume of material that you can sell and consequently filling up your landfill faster.

Orange County, North Carolina switched from dual to single stream recycling in 2014. In the first year of the program, the volume of recycled material grew by an impressive 16%. This improvement is part of a long-term trend. In 1991-1992, Orange County landfilled 1.36 tons of waste per person per year. This value has now dropped to 0.49 tons, a decrease of 64%. While this is an impressive improvement, we still landfill approximately twice the amount of the average person in the European Union.

In order for Orange County to catch up with the French, the Danes, and the Czechs, we need to maximize the amount of material we recycle while not putting inappropriate material in the bin. Follow this link to the list from Orange County Solid Waste for an explanation of what can and cannot be recycled. Post the recycle guidelines near your recycle bin and check before you throw!

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