Recycling by material

Concrete recycling is the use of rubble from demolished concrete structures. Recycling is cheaper and more ecological than trucking rubble to a landfill.[3] Crushed rubble can be used for road gravel, revetments, retaining walls, landscaping gravel, or raw material for new concrete. Large pieces can be used as bricks or slabs, or incorporated with new concrete into structures, a material called urbanite.[4][5]

Glass recycling is the processing of waste glass into usable products. Glass that is crushed or imploded and ready to be remelted is called cullet.[6] There are two types of cullet: internal and external. Internal cullet is composed of defective products detected and rejected by a quality control process during the industrial process of glass manufacturing, transition phases of product changes (such as thickness and color changes) and production offcuts. External cullet is waste glass that has been collected or reprocessed with the purpose of recycling. External cullet (which can be pre- or post-consumer) is classified as waste. The word "cullet", when used in the context of end-of-waste, will always refer to external cullet.

To be recycled, glass waste needs to be purified and cleaned of contamination. Then, depending on the end use and local processing capabilities, it might also have to be separated into different sizes and colours. Many recyclers collect different colors of glass separately since glass retains its color after recycling. The most common colours used for consumer containers are clear (flint) glass, green glass, and brown (amber) glass. Glass is ideal for recycling since none of the material is degraded by normal use.

Many collection points have separate bins for clear (flint), green and brown (amber). Glass re-processors intending to make new glass containers require separation by color, because glass tends to retain its color after recycling. If the recycled glass is not going to be made into more glass, or if the glass re-processor uses newer optical sorting equipment, separation by color at the collection point may not be required. Heat-resistant glass, such as Pyrex or borosilicate glass, must not be part of the glass recycling stream, because even a small piece of such material will alter the viscosity of the fluid in the furnace at remelt.

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Plastic recycling is the processing of plastic waste into other products.[18][19][20] Recycling can reduce dependence on landfill, conserve resources and protect the environment from plastic pollution and greenhouse gas emissions.[21][22] Recycling rates lag those of other recoverable materials, such as aluminium, glass and paper. Through 2015, the world produced some 6.3 billion tonnes of plastic waste, only 9% of which has been recycled, and only ~1% has been recycled more than once.[23] Additionally, 12% was incinerated and the remaining 79% sent to landfill or to the environment including the ocean.[23]

Almost all plastic is not biodegradable and absent recycling, spreads across the environment[24][25] where it can cause harm. For example, as of 2015 approximately 8 million tons of waste plastic enter the oceans annually, damaging the ecosystem and forming ocean garbage patches.[26]Even the highest quality recycling processes lead to substantial plastic waste during the sorting and cleaning process, releasing large amounts of microplastics in waste water, and dust from the process.[27][28]

Almost all recycling is mechanical: melting and reforming plastic into other items. This can cause polymer degradation at a molecular level, and requires that waste be sorted by colour and polymer type before processing, which is complicated and expensive. Errors can lead to material with inconsistent properties, rendering it unappealing to industry.[29] In feedstock recycling, waste plastic is converted into its starting chemicals, which can then become fresh plastic. This involves higher energy and capital costs. Alternatively, plastic can be burned in place of fossil fuels, in energy recovery facilities or biochemically converted into other useful chemicals for industry. In some countries, burning is the dominant form of plastic waste disposal, particularly where landfill diversion policies are in place.

Plastic recycling is low in the waste hierarchy. It has been advocated since the early 1970s,[30] but due to economic and technical challenges, did not impact plastic waste to any significant extent until the late 1980s. The plastics industry has been criticised for lobbying for expansion of recycling programs, even while research showed that most plastic could not be economically recycled.[31][32]