Recycling involves processing used materials into new products in order to prevent waste of potentially useful materials, reduce the consumption of fresh raw materials, reduce energy usage, reduce air pollution (from incineration) and water pollution (from landfilling) by reducing the need for “conventional” waste disposal, and lower greenhouse gas emissions as compared to virgin production. Recycling is a key component of modern waste management and is the third component of the “Reduce, Reuse, Recycle” waste hierarchy.
Recyclable materials include many kinds of glass, paper, metal, plastic, textiles and electronics. Although similar in effect, the composting or other reuse of biodegrabale waste- such as food or garden waste- is not typical considered recycling. Materials to be recycled are either brought to a collection center or picked up from the curbside, then sorted, cleaned up, and reprocessed into new materials bound for manufacturing.
In a strict sense recycling of a material would produce a fresh supply of the same material, for example, used office paper to more office paper, or used foamed polystyrene to more polystyrene. However, this is often difficult or too expensive (compared with producing the same product from raw materials or other sources), so “recycling” of many products or materials involves their reuse in producing different materials (e.g., cardboard) instead. Another form of recycling is the salvage of certain materials from complex products, either due to their natural value (e.g., lead from car batteries, or gold from computer components), or due to their hazardous nature (e.g., removal and reuse of mercury from various items).
Critics dispute the net economic and environmental benefits of recycling over its costs. Specififically, critics argue that the costs and energy saved in collection and transportation detract from (and possibly outweigh) the costs and energy saved in the production process, also that the jobs produced by the recycling industry production, can be a poor trade for the jobs lost in logging, mining and other industries associated with virgin production, and that the materials such as paper pulp can only be recycled few times before material degradation prevents further recycling. Proponents of recycling counter each of these claims, and the validity of arguments from both sides led to enduring controversy.
Early recycling: recycling has been a common practice for most of human history, which recorded advocates as far back as Plato in 400 BC (Greek, 428/427 BC – 348/347 BC, was a Classical Greek philosopher, mathematician, writer of philosophical dialogues.Academy in Athens, the first institution of higher learning in the Western world. Along with his mentor, Socrates, and his student, Aristotle, Plato helped to lay the foundations of natural philosophy, science, and Western philosophy. Plato was originally a student of Socrates). During periods when resources were scarce, archeological studies of ancient waste dumps show less household waste ( such as ash, broken tools and pottery)- implying more waste was being recycled in the absence of new material.
In pre-industrial times, there is evidence of scrap bronze and other metals being collected in Europe and melted down for perpetual reuse. In Britain dust and ash from wood and coal fires was collected by “dustmen” and downcycled as a base material use in brick making. The main driver for these types of recycling was the economic advantage of obtaining recycled feedstock instead of acquiring virgin material, as well as a lack of public waste removal in ever more densely populated areas.
Resource shortages caused by the world was, on other such world-changing ocurrences greatly encouraged recycling. Massive government promotion campaigns were carried out in the World War II in every country involved in the war, urging citizens to donate metals and conserve fibre, as a matter of signigicant patriotic importance. Resource conservation programs established during the war were continued in some contries without an abundance of natural resources, such as Japan, after the war ended.
The next big investment in recycling occured in the 1970s, due to rising energy costs. Recycling aluminium use only 5% of the energy required by virgin production, glass, paper and metals have less dramatic but very significant energy savings when recyclind feedstock is used.
Collection: A number of different systems have been implemented to collect recyclables from general waste stream. These systems tend to lie along the spectrum of trade-off between public convenience and government ease and expense. The three main categories of collestion are “drop-off centres” and “curbside collection”.
Dro-off centres require the waste producer to carry the recyclables to central location, either and installed or mobile collection station for the reprocessing plant itself. They are the easiest type of collection to establish, but suffer from low and unpredictable throughput. Buy-back centres differ in that the cleaned recyclables are purchased, thus providing a clear incentive for use and creating a stable supply. The subsides are necessary to make buy-back centres a viable enterprise.
Curbside collection: Curbside collection encompasses many subtly different systems, which differ mostly on where in the process the recyclables are sorted and cleaned. The main categories are mixed waste collection, commingled recyclables and source separation. A waste collection vehicule generally picks up the waste.
At one end to the spectrum is mixed waste collection, in which all recyclables are collected mixed in with the rest of the waste, and the desired material is then sorted out and cleaned at a central sorting facility. This results in a large amount of recyclable waste, paper especially, being too soiled to reprocess but has advantages as well, the city need to pay for a separate collection of recyclables and not public education is needed. Any changes to which materials are recyclable is easy to accomodate as all sorting happens in a central location.
In a commingled or single- stream system, all recyclables for collection are mixed but kept separate from other waste. This greatly reduces the need for post-collection cleaning but does require public education on what materials are recyclable.
Source separation is the other extreme, where each material is cleaned and sorted prior to collection. This method requires the last post-collection sorting and produces the purest recyclables, but incurs additional operating costs for collection of each separate material. An extensive public education program is also required, which must be successful if recyclables contamination is to be avoided.
Source separation used to be the preferred method due to the high sorting costs incurred by commingled collection. Advances in sorting technology (explained in “Sorting” paragrapgh below), however, have lowered this overhead substantially-many areas which had developed source separation programs have since switched to commingled collection.
Sorting: Once commingled recyclables are collected and delivered to a central collection facility, the different types of materials must be sorted. This is done in a series of stages, many of which involve automated process such as the truck-load of material can be fully sorted in less than an hour. Some plants can now sort the materials automatically, known as Singke Stream. A 30% increase in recycling rates has been seen in the areas where these plants exist.
Initially the commingled recyclables are removed from the collection vehicle and placed on a conveyor belt spread out in a single layer. Large pieces of cardboard and plactic bags are removed by hand at this stage, as they can cause later machinery to jam.
Next automated machinary separates the recyclables by weight, splitting lighter paper and plastic from heavier glass and metal. Cardboard is removed from the mixed paper, and the most common types of plastic, PET(#1) and HPDE (#2), are collected. This separation is usually done by hand, but has become automated in some sorting centres, a spectroscopic scanner is used to differentiate between different types pf paper and plastic based on the absorbed wavelenghts (lenght of wave cycle), and subsequently divert each material into the proper collection channel.
Strong magnets are used to separate out ferrous metals, such as iron, steel, and thin-plated steel cans (“tin cans”). Non-ferrous metals are ejected by magnetic eddy currents in which a rotating magnetic field induces an electric current around the aluminium cans, which in turn creates a magnetic eddy current inside the cans. This magnetic eddy current is repulsed by a large magnetic field, and the cans are ejected from the rest of the recyclable stream.
Finally, glass must be sorted by hand based on its color: brown, amber, green or clear.
Many different materials can be recycled but each type requires different technique.
Aggregates and concretes: Concrete aggregate collected from demolition sites is put through a crushing machine, often along with asphalt, bricks, dirt, and rocks. Smaller pieces of concrete are used as gravel for new construction projects. Crushed recycled concrete can also be used as the dry aggregate for brand new concrete if it is free of contaminants. This reduces the need for other rocks to be dug up, which in turn saves trees and habitats.
Batteries: The large variation in size and type of batteries makes their recycling extremely difficult, they must first be sorted into similar kinds and each kind requires an individual process. Additionally, older batteries contain mercury and cadmium (mettalic chemical element), harmful materials which must be handled with care. Because of their potential environmental damage, proper disposal of used batteries is required by law in many areas. Unfortunately, this mandate has been difficult to enforce.
Lead-acid batteries, like those used in automobiles, are relatively easy to recycle.
Biodegradable waste: Kitchen, garden, and other green waste can be recycled into useful material by composting. This process allows natural aerobic material to break down the waste into fertile topsoil. Must composting is done on a household scale, but municipal green-waste collection programs also exist. The programs can supplement their funding by selling the topsoil produced.
Clothing: Recycling clothe via consignment or swapping has become increasingly popular. In a clothing swap, a group of people gather at a venue to exchange clothes amongst each other.
Electronics disassembly and reclamation: The direct disposal of electrical equipment, such as old computers and mobile phones, is banned in many areas due to toxic contents of certain components. The recycling process works by mechanically separating the metals, plastics, and circuit boards contained in the appliance. When this is done on a large scale at an electronic waste recycling plant, component recovery can be archived in cost-effective.
Ferrous metals: Iron and steel are the world’s most recycled materials, and among the easiest to reprocess, as they can be separated magnetically from the waste stream. Recycling is via a steelworks, scrap is either remelted in an electric arc furmace (90-100%scrap), or used as the part of the charge in a basic Oxygen furnace (around 25%). Any grade of steel can be recycled to top quality new metals, with no “downgrading” from prime to lower quality materials as steel is recycled repeatedly. 42% of crude steel product is recycled material.
Non-ferrous metals: Aluminium is the most efficient and widely-recycled materials. Aluminium is shredded and ground into small pieces or crushed into bales. These pieces or bales are melted in an aluminium smelter to produce molten aluminium. By this stage the recycled aluminium is indistinguishable from virgin aluminium and further processin is identical for both. This process does not produce any change in the metal, so aluminium can be recycled indefinitely.
Recycling aluminium saves 95% of the energy cost of processing new aluminium. This is because the temperature necessary for melting recycled, nearly pure, aluminium is 600 °C, while to extract mined aluminium from its ore requires 900 °C. To reach this higher temperature, much more energy is needed, leading to the high environmental benefits of environmental benefits of aluminium recycling. Also the energy saved by recycling one aluminium can is enough to run a television for 3 hours.
Glass: Glass bottles and jars are gathered then sorted into color categories. The collected glass cullet is taken to a glass recycling plant where it is monitored for purity and contaminants are removed. The cullet is crushed and added to a raw material mix in a melting furnace. It is then mechanically blown or molded into new jars or bottles. Glass cullet is also used in the construction industry for aggregate and glassphalt. Glassphalt is a road-laying material which comprises around 30% recycled glass. Glass can be recycled indefinitely as its structure does not deteriorate when reprocessed.
Paper: Paper can be recycled by reducing it to pulp and combining it with pulp from newly harvested wood. As the recycling process causes the paper fibres to break down, each time paper is recycled its quality decreases. This means that either a higher percentage of new fibres must be added, or the paper downcycled into lower quality products. Any writing or colouration of the paper must first be removed by deinking, which also removes fillers, clays, and fibre fragments.
Almost all paper can be recycled today, but some types are harder to recycle than others. Paper coated with plastic or aluminium foil, and paper that are waxed, pasted, or gummed are usually not recycled because the process is too expensive. Gift-wrap paper also cannot be recycled due to its already poor quality.
Plastic: Plastic recycling is the process of recovering scrap or waste plastics and reprocessing the material into useful products. Compared to glass or metallic materials, plastic poses unique challenges. Because of the massive number of types of plastic, they each carry a resin identification code, and must be sorted before they can be recycled. This can be costly, while metals can be sorted using electromagnets, not such “easy sorting” capability exists for plastics. In addition to this, while labels do not need to be removed from bottles for recycling, lids are often made from a different kind of non-recyclable plastic.
To help in identifying the materials in various plastic items, resin identification code numbers 1-6 have been assigned to six common kinds of recyclable plastic resins, with the number 7 indicating any other kind of plastic, whether recyclable or not. Standardized symbols are available incorporating each of these resin codes.
Textiles: When considering textile recycling one must understand what the material consists of most textiles are composites of cotton (biodegradable material) and synthetic plastics. The textile’s composition will affect its durability and method of recycling.
Workers sort and separate collected textiles into good quality clothing and shoes which can be reused or worn. There is a trend of moving these facilities from developed countries to developing countries either for charity or sold for cheaper price. Usually, international organisations collect used textiles from developed countries as a donation to those third world countries. This recycling practice is encouraged because it helps to reduce unwanted waste while providing clothing to those in need. Damaged textiles are further sorted into grades to make industrial wiping cloths and use in paper manufacture or material suitable for fibre reclamation and filling products. If textile reprocessors receive wet or soiled clothes however, these may still disposed of in a landfill, as the washing and drying facilities are not present at sorting units.
Wood: Recycling wood has become popular due to its image as an environmentally friendly product, with consumers commonly beleiving that by purchasing recycling wood the demand will fall and ultimately benefit the environment. The arrival of recycled wood as a construction product has been important in both raising industry and consumer awarness towards deforestation and promoting wood mills to adopt environmentally friendly practices.
Other techniques: Several other materials are also commonly recycled, frequently at an industrial level.
Ship breaking is one example that has associated environmental, health, and safety risks for the area where the operation takes place, balancing all these considerations is a environmental justice problem.
Tyre recycling is also common. Used tyres can be added to asphalt for producing road surfaces or to make rubber much used on playgrounds for safety. There are also often used as the insulation and heat absorbing/releasing material in specially constructed homes known as earthships.