Courtesy  :  Wikipedia

recycling

Recycling is the process of converting waste materials into new materials and objects. The recovery of energy from waste materials is often included in this concept. The recyclability of a material depends on its ability to reacquire the properties it had in its original state.^[1] It is an alternative to “conventional” waste disposal that can save material and help lower greenhouse gas emissions. It can also prevent the waste of potentially useful materials and reduce the consumption of fresh raw materials, reducing energy use, air pollution (from incineration) and water pollution (from landfilling).

Recycling is a key component of modern waste reduction and is the third component of the “Reduce, Reuse, and Recycle” waste hierarchy.^[2][3] It promotes environmental sustainability by removing raw material input and redirecting waste output in the economic system.^[4] There are some ISO standards related to recycling, such as ISO 15270:2008 for plastics waste and ISO 14001:2015 for environmental management control of recycling practice.

Recyclable materials include many kinds of glass, paper, cardboard, metal, plastic, tires, textiles, batteries, and electronics. The composting and other reuse of biodegradable waste—such as food and garden waste—is also a form of recycling.^[5] Materials for recycling are either delivered to a household recycling center or picked up from curbside bins, then sorted, cleaned, and reprocessed into new materials for manufacturing new products.

In ideal implementations, recycling a material produces a fresh supply of the same material—for example, used office paper would be converted into new office paper, and used polystyrene foam into new polystyrene. Some types of materials, such as metal cans, can be remanufactured repeatedly without losing their purity.^[6] With other materials, this is often difficult or too expensive (compared with producing the same product from raw materials or other sources), so “recycling” of many products and materials involves their reuse in producing different materials (for example, paperboard). Another form of recycling is the salvage of constituent materials from complex products, due to either their intrinsic value (such as lead from car batteries and gold from printed circuit boards), or their hazardous nature (e.g. removal and reuse of mercury from thermometers and thermostats

Recyclates

“Recyclate” is a raw material sent to and processed in a waste recycling plant or materials-recovery facility^[37] so it can be used in the production of new materials and products. For example, plastic bottles can be made into plastic pellets and synthetic fabrics.^[38]

Quality of recyclate

The quality of recyclates is one of the principal challenges for the success of a long-term vision of a green economy and achieving zero waste. It generally refers to how much of it is composed of target material, versus non-target material and other non-recyclable material.^[39] Steel and other metals have intrinsically higher recyclate quality; it is estimated that two-thirds of all new steel comes from recycled steel.^[40] Only target material is likely to be recycled, so higher amounts of non-target and non-recyclable materials can reduce the quantity of recycled products.^[39] A high proportion of non-target and non-recyclable material can make it more difficult to achieve “high-quality” recycling; and if recyclate is of poor quality, it is more likely to end up being down-cycled or, in more extreme cases, sent to other recovery options or landfilled.^[39] For example, to facilitate the remanufacturing of clear glass products, there are tight restrictions for colored glass entering the re-melt process. Another example is the downcycling of plastic, where products such as plastic food packaging are often downcycled into lower quality products, and do not get recycled into the same plastic food packaging.

The quality of recyclate not only supports high-quality recycling, but it can also deliver significant environmental benefits by reducing, reusing, and keeping products out of landfills.^[39] High-quality recycling can support economic growth by maximizing the value of waste material.^[39] Higher income levels from the sale of quality recyclates can return value significant to local governments, households and businesses.^[39] Pursuing high-quality recycling can also promote consumer and business confidence in the waste and resource management sector, and may encourage investment in it.

There are many actions along the recycling supply chain, each of which can affect recyclate quality.^[41] Waste producers who place non-target and non-recyclable wastes in recycling collections can affect the quality of final recyclate streams, and require extra efforts to discard those materials at later stages in the recycling process.^[41] Different collection systems can induce different levels of contamination. When multiple materials are collected together, extra effort is required to sort them into separate streams and can significantly reduce the quality of the final products.^[41] Transportation and the compaction of materials can also make this more difficult. Despite improvements in technology and quality of recyclate, sorting facilities are still not 100% effective in separating materials.^[41] When materials are stored outside, where they can become wet, can also cause problems for re-processors. Further sorting steps may be required to satisfactorily reduce the amount of non-target and non-recyclable material.^[41]

Recyclate Quality Action Plan (Scotland)

Scotland’s Recyclate Quality Action Plan proposes a number of actions the Scottish Government wants to take to increase the quality of materials collected for recycling and sorted at recovery facilities before it is exported or sold on the reprocessing market.^[41] Its objectives are to:^[42]

• Increase recyclate quality, and create greater transparency about it.
• Help those contracting with recycling facilities identify what is required of them.
• Ensure compliance with the Waste (Scotland) Regulations 2012.
• Stimulate a household market for quality recyclate.
• Address and reduce issues around waste shipment regulations.

The plan focuses on three key areas, with 14 actions to increase the quality of materials collected, sorted and presented to the processing market in Scotland.^[42] These areas are:^[41]

• Collection systems and input contamination
• Sorting facilities—material sampling and transparency
• Material quality benchmarking and standards

Recycling consumer waste

Collection

A number of systems have been implemented to collect recyclates from the general waste stream, occupying different places on the spectrum of trade-off between public convenience and government ease and expense. The three main categories of collection are drop-off centers, buy-back centers and curbside collection.^[5] About two-thirds of the cost of recycling is incurred in the collection phase.^[43]

Curbside collection

Curbside collection encompasses many subtly different systems, which differ mostly on where in the process the recyclates are sorted and cleaned. The main categories are mixed waste collection, commingled recyclables, and source separation.^[5] A waste collection vehicle generally picks up the waste.

In mixed waste collection, recyclates are collected mixed with the rest of the waste, and the desired materials are sorted out and cleaned at a central sorting facility. This results in a large amount of recyclable waste (especially paper) being too soiled to reprocess, but has advantages as well: The city need not pay for the separate collection of recyclates, no public education is needed, and any changes to the recyclability of certain materials are implemented where sorting occurs.^[5]

In a commingled or single-stream system, recyclables are mixed but kept separate from non-recyclable waste. This greatly reduces the need for post-collection cleaning, but requires public education on what materials are recyclable.^[5][8]

Source separation

Source separation is the other extreme, where each material is cleaned and sorted prior to collection. It requires the least post-collection sorting and produces the purest recyclates. However, it incurs additional operating costs for collecting each material, and requires extensive public education to avoid recyclate contamination.^[5] In Oregon, USA, Oregon DEQ surveyed multi-family property managers; about half of them reported problems, including contamination of recyclables due to trespassers such as transients gaining access to collection areas.^[44]

Source separation used to be the preferred method due to the high cost of sorting commingled (mixed waste) collection. However, advances in sorting technology have substantially lowered this overhead, and many areas that had developed source separation programs have switched to what is called co-mingled collection.^[8]

Buy-back centers

At Buy-back centers, separated, cleaned recyclates are purchased, providing a clear incentive for use and creating a stable supply. The post-processed material can then be sold. If profitable, this conserves the emission of greenhouse gases; if unprofitable, it increases their emission. Buy-back centres generally need government subsidies to be viable. According to a 1993 report by the U.S. National Waste & Recycling Association, it costs an average $50 to process a ton of material that can be resold for $30.^[5]

In the US, the value per ton of mixed recyclables was $180 in 2011, $80 in 2015, and $100 in 2017.^[45]

In 2017, glass was essentially valueless because of the low cost of sand, its major component. Similarly, low oil costs thwarted plastic recycling.^[45]

In 2017, Napa, California was reimbursed about 20% of its recycling costs.^[45]

Drop-off centers

Drop-off centers require the waste producer to carry recyclates to a central location—either an installed or mobile collection station or the reprocessing plant itself. They are the easiest type of collection to establish but suffer from low and unpredictable throughput.

Distributed recycling

For some waste materials such as plastic, recent technical devices called recyclebots^[46] enable a form of distributed recycling. Preliminary life-cycle analysis (LCA) indicates that such distributed recycling of HDPE to make filament for 3D printers in rural regions consumes less energy than using virgin resin, or using conventional recycling processes with their associated transportation.^[47][48]

Sorting

Once commingled recyclates are collected and delivered to a materials recovery facility, the materials must be sorted. This is done in a series of stages, many of which involve automated processes, enabling a truckload of material to be fully sorted in less than an hour.^[8] Some plants can now sort materials automatically; this is known as single-stream recycling. Automatic sorting may be aided by robotics and machine learning.^[49][50] In plants, a variety of materials is sorted including paper, different types of plastics, glass, metals, food scraps, and most types of batteries.^[51] A 30% increase in recycling rates has been seen in areas with these plants.^[52] In the US, there are over 300 materials recovery facilities.^[53]

Initially, commingled recyclates are removed from the collection vehicle and placed on a conveyor belt spread out in a single layer. Large pieces of corrugated fiberboard and plastic bags are removed by hand at this stage, as they can cause later machinery to jam.^[8]

Next, automated machinery such as disk screens and air classifiers separate the recyclates by weight, splitting lighter paper and plastic from heavier glass and metal. Cardboard is removed from mixed paper, and the most common types of plastic—PET (#1) and HDPE (#2)—are collected, so these materials can be diverted into the proper collection channels. This is usually done by hand; but in some sorting centers, spectroscopic scanners are used to differentiate between types of paper and plastic based on their absorbed wavelengths.^[8] Plastics tend to be incompatible with each other due to differences in chemical composition; their polymer molecules repel each other, similar to oil and water.^[54]

Strong magnets are used to separate out ferrous metals such as iron, steel and tin cans. Non-ferrous metals are ejected by magnetic eddy currents: A rotating magnetic field induces an electric current around aluminum cans, creating an eddy current inside the cans that is repulsed by a large magnetic field, ejecting the cans from the stream.^[8]

Finally, glass is sorted according to its color: brown, amber, green, or clear. It may be sorted either by hand,^[8] or by a machine that uses colored filters to detect colors. Glass fragments smaller than 10 millimetres (0.39 in) cannot be sorted automatically, and are mixed together as “glass fines”.^[55]

In 2003, San Francisco‘s Department of the Environment set a citywide goal of zero waste by 2020.^[56] San Francisco’s refuse hauler, Recology, operates an effective recyclables sorting facility that has helped the city reach a record-breaking landfill diversion rate of 80% as of 2021.^[57] Other American cities, including Los Angeles, have achieved similar rates.