Taking the time to sort is essential because it helps ensure that recyclables are recycled correctly. Sorting also means that less waste is sent to landfills. Contaminants such as plastic bags, styrofoam, and food waste can contaminate recycling loads. If a load is too contaminated, it can be rejected by the processor and end up in the landfill.
Some recycling companies require that different types of recyclables be placed into separate bins (multi-stream recycling); others allow paper and plastic packaging and cartons to be collected together in the same bin (single-stream recycling). Regardless of how your company collects, you must know the waste management accepted recyclables. This helps limit the number of items collected with your recycling that end up in landfills because they aren’t accepted at the processing plant. Most materials recovery facilities, or MRFs, have manual and mechanical sorting technologies. These are designed to produce the highest quality recycled materials for a reasonable cost. A contaminated batch of recycled materials is costly, requires more manual sorting, and can jam machinery. It also decreases the value of the recycled material and could send it to a landfill.
Contaminants can be anything from food waste and liquids to metal lids on glass containers. A bit of food residue can ruin the fiber in paper and render it unrecyclable, while a liquid can spill over into another container, rendering it unusable. Metal lids must be removed from glass containers, and the container itself needs to be clean of all residues. This may mean a quick rinse or even a soak in some water. If you can’t get a container completely clean, it is better to throw it away than to risk the contamination of your other recyclables.
In a perfect world, all recyclables would be collected in one bin and then efficiently sorted at the recycling plant. Unfortunately, the rules of waste sorting vary from country to country and sometimes even city to city. Some countries require paper, metal, and glass to be placed in separate bins (multi-stream recycling). In contrast, others allow plastic packaging and food containers to be mixed with cardboard and paper products (single-stream).
When co-mingled recyclables are deposited at an MRF, they must first be manually sorted. Trained humans look through the co-mingled waste and remove any items that can’t be recycled, large pots and pans, badly contaminated materials, such as greasy pizza boxes or unwashed peanut butter jars, and plastic bags, which can clog machines used to sort the other types of recyclables. The remaining waste must then be separated into their polymers. Chopped mixed plastics are spread across a conveyor and then identified using near-infrared (NIR) spectroscopy, which detects unique absorbance peaks in the NIR spectrum of each polymer. When the machine recognizes the correct polymer, air jets blow each plastic fragment into its corresponding processing stream. Despite the importance of accurate sorting, many recyclables still end up in landfills even though they’re technically “recyclable.” This is due to poor recycling habits at home, which lead to contamination. The contaminants mentioned above cost money to remove and cause problems further down the line regarding the salability of the resulting recycled material. Plastic bags, for example, can wrap around the shafts and axles of machinery, causing them to break. This increases the risk of injury for the people operating the equipment and can also add to the cost of running the machine, ultimately impacting the price of the finished recycled product.
Metals are a precious resource, so it’s important to recycle them correctly. The first step is to separate them from other recycling materials, especially paper, glass, and plastic. Then, they can be sent to a metal processor for recovery and reuse. Some items that may seem recyclable are not. For example, greasy pizza boxes and unwashed peanut butter jars are contaminants that reduce the salability of an entire load of recycled material. If a batch of recycling is contaminated, the buyers will not want it, and it will end up in landfills instead of being made into new products. The atomic structure of metals makes them weak in terms of their desire for electrons. When two metal atoms bond, they don’t care which one gets the extra electrons. This differs from the chemical bonds when non-metal atoms (like chlorine) steal electrons from a metal atom. The end-of-life recycling rates for some critical metals – including rare earth metals – are so low that they can serve as “mines above ground.” These resources will eventually run out, so people must understand what’s recyclable and how to properly prepare it for the long journey through the recycling stream. This knowledge will improve the overall quality of our recycling streams and benefit the environment.
Glass is one of the most common recyclables, but it’s also a complex material to recycle. It’s heavy, and shipping it long distances is costly. This is why sorting is so important when it comes to glass recycling. When glass bottles and jars are recycled, they travel to massive sorting centers. There, automated equipment separates them according to color and composition. They are sorted into different categories and then shipped to the appropriate manufacturers for further processing. Because of its potential pozzolanic activity, waste glass can be used as either a partial clinker replacement or a cement additive. This section investigates the past research into these two options and their varying effects on mechanical properties. Using waste glass as a partial clinker replacement reduces the raw materials required to make glass. It also helps lower the temperature during melting and can improve kiln efficiency by reducing abrasion. The use of glass as a cement additive also has many advantages. The low cost of glass compared to its primary raw materials makes it an attractive alternative. However, its smooth surface interferes with forming a solid bond between coarse aggregate and cement paste. As a result, its performance as a coarse aggregate is limited. Nonetheless, it still produces promising results as a substitute for traditional aggregates.