Waste Amount and Waste Management
As a natural byproduct of product consumption as well as product manufacturing waste is generated, and while companies and consumers strive for reducing its amount, to help sustainability and efficiency, the fact of the matter is, the amount of waste is not reducing and is projected to increase by as much as 70% in the next 30 years (the World Bank, 2018) – these are catastrophic levels that require urgent action. As much as 69.7% of that waste is currently landfilled or otherwise dumped, making the waste management process very inefficient, as can be seen from the World Bank figure below.
Reusing Old Items
Products that are discarded after use and reused without modifications, for example being sold on to other consumers on the secondary market or donated can be an effective way to reduce the number of waste output at a given time, as some of the products are discarded while still being able to perform their functions, or requiring minimal repair. Such reuse of products by other parties is also referred primary recycling (Recycling Consortium, 2014).
Recycling and Upcycling
This method of dealing with “unneeded” products involves modification of the products or use by parts to serve an alternative purpose – this often leads to reuse for aesthetic purposes, such as decorations or fashion/clothing. This so called secondary recycling (Recycling Consortium, 2014) can also mean reuse of the materials without significant chemical reactions, such as using rubber tires for soft surfaces (Eco Green Equipment, 2016) or unconventional materials for low load construction materials, going as a far as utilizing freeze dried blood in brick manufacturing (City Metrics, 2015).
Dumping rubbish at a landfill is an age-old method of waste management and in some forms can serve as a temporary storage of materials that will be later recycled or incinerated (possibly with energy recovery), options that will be discussed later. In these cases, landfill acts as a temporary storage for the products and extends their lifecycle in a time and space inefficient manner. However, landfill can also act as a final stage of the recyclable product lifecycle, similarly to how non-recyclable materials are dealt with.
Unfortunately, these methods do not directly deal with removing waste and satisfying material or energy demand, but rather store it in a different form until it is discarded. At the same time primary and secondary recycling are excellent ways to increase sustainability of non-recyclable materials.
While it is difficult to survey comprehensive information on waste on large scale and data can be seen as rough estimate at best, as shown in the figure above obtained from a World Bank report, the most significant recyclable material groups among the waste thrown away globally are: It should also be noted, that these materials are recovered for recycling at different rates (on average less than 50%), as global recycling rates are as low as 13.5%. And while paper can be recycled multiple times and is easier to sort for consumers, reaching recycling rates of as high as 66.8% in developed countries (Sukalich, 2016), plastics cannot be recycled as often and contain a lot less recyclable material (as thermosets/elastomers are not typically recyclable).
Recycling of Paper & Cardboard
Depending on the location or council, paper can be collected by different categories, often including mixed (for paper, glossy magazines & cardboard) or office paper only. After collecting the paper from the recycling containers it is sorted using a mix of manual and automated sorting – for example rollers for mass separation (cardboard vs paper), digital vision for color separation or manual separation of plastic and foreign objects (British Broadasting Company, 2015).
After paper is separated from other waste and sorted by grade and type (Complete Recycling, LLC, n.d.), the paper is cleaned from inks, adhesives, staples and other contaminants by washing and wetting it with soap & chemicals and water to separate the fibers and transform the paper into a “pulp”. This pulp is continuously cleaned of inks and contaminants using chemicals, screens and filters as it is mixed. Pulp is then absorption-dried, rolled, pressed and heated to create a sheet of recycled paper (Sukalich, 2016). Depending on source, additives, thickness and geometry a different type of paper product is made. It can then be treated to give it a colour or texture, ironed to remove unnecessary wrinkles and rolled for bulk transportation. Rolls are quality checked and graded and can then be cut or used by manufacturers (British Broadasting Company, 2015).
Paper fibers cannot be recycled indefinitely – cellulose fibers can only be recycled about 5-7 times before becoming too short and brittle, as it is broken down during pulping, chemical processing and cutting (Environmental Protection Agency, 2016). Longer fiber paper has more flexibility and produces higher grade stock at the end of recycling process, while shorter fiber paper is used for making other short fiber, lower grade paper, such as in newspaper. As such, upon recycling the paper can only be used for making other paper products of equal or lower grade (unless “virgin” material is added (New York Times, 2010)).
Recycling Plastics
Depending on the location, the consumer plastics are categorized for recycling in different ways prior to curbside collection: Of these, categories from 3 to 7 are not widely recycled either due to toxins, difficulty of processing or a small market size (EarthEasy, 2012).
Material is then washed, steamed and treated with chemicals to remove labels and surface contaminants. The plastics are then sorted manually, by mass and using near infrared vision (as different plastics can react and change colour when sufficiently heated), this important step helps remove non recyclable plastics and non-plastic materials, for example “PVC bottles turning slightly brown, providing for easier identification and removal “ (The Balance SMB, 2018).
When the plastic is appropriately separated into categories, it is processed by first cutting and grinding the products into flakes. These are then washed, disinfected and decontaminated to provide highest quality output. Flakes are also separated by density using sink/float baths which can also help separate foreign materials which were integrated/fixed in the plastic parts. The flakes are then rinsed and dried, after which they are ready for use by manufacturers (The Balance SMB, 2018).
In order to achieve an even higher purity (and thus quality), some recycling plants utilize a “melt filtering” process, where the cleaned flakes are molten and passed through series of screens that stop any unmolten impurities that were left in by earlier processes. The melt is then extruded into pellets of higher quality plastic ready for use (The Balance SMB, 2018).
Problems caused by changes to structure and characteristics
Unfortunately, plastics experience a wide range of changes to their characteristics that are important for their applications: Aesthetics suffer as a result of recycled plastics developing defects, such as visible flowlines, poor surface finish making it difficult to paint or have glossy products and trace of metallic particles. A lower selection of colours is available among recycled plastics. This makes recycled plastics less desirable for use in parts visible to consumers (Ellen Macarthur Foundation, 2017). Moreover, some contaminants even cause an unattractive smell in a recycled plastic product or may be toxins making the recycled material unsuitable for use in food containers (Wageningen University & Research, n.d.)
Listed mechanical characteristics are also reduced which can be corrected by changes to part geometry (e.g. wall thickness), but more importantly they experience larger variations than those of their new counterparts and as such are less suitable for critical parts (Drummond, 2015). Contaminants can also affect the manufacturability of the output plastics, reducing their potential to be film extruded or blow moulded.
Recycling Metal
Unlike plastics and paper, virgin metal materials cannot be made sustainably and always utilize metal ore, which is a limited supply. Together with metals’ excellent recyclability, this creates a lot of demand and value for metal scrap. Metal recycling process not only reduces demand for ores, but also uses less energy than virgin metal extraction – with reductions of as much of 56% for steel and over 90% for aluminium (The Balance SMB, 2018). This means that metals have a very high recovery rate and while only around 30% of metal is recycled currently, nearly 40% of global steel production uses recycled steel
Collection and Sorting of Metal
Metals are considered more valuable (many non-ferrous metals especially) as their supply is limited and as such the scrap retains a higher cost and is less likely to end up in a landfill or an open dump. After collecting the metals curbside or having a direct aggregated delivery to the sorting facility (e.g. excess trimmings from a metal stamping process), the metals are sorted by type, using color (e.g. yellow/red copper, light gray aluminium), density and, very importantly, their magnetism – which usually indicates ferrous metals (n.b. – electromagnets can be used to separate even nonferrous metals from general waste stream) (Rick Leblanc, 2018)
The categorized metals are then shredded and melted at an appropriate temperature, before they are decontaminated to remove any remains of non-metal materials or alloys of different melting temperatures and densities. A common purification technique used to increase metal quality is electrolysis, which will leave pure metal a the poles while letting sink the impurities that would otherwise contaminate and alter the metal characteristics, making it for example more brittle or less conductive (Anglia Campus, n.d.).
