Due to increased the high residence time in the environment, old and used plastics require recycling to not only ensure clean and healthy environment, but also maximize the resource utility. Sorting/ separation is one of the most important stage in the recycling process as it differentiates the plastics from other materials and categorize it into various forms. Depending on the origin of the plastic materials, the sorting process is made easier especially if there was initial separation at the source where plastics are put in different containers from the others types of wastes.
Physical sorting method According to Plunket (2005), this separation method involves use of the visible and physical characteristics of the plastics to remove them from other waste materials or separate different types of plastics. This method is labor intensive as it requires manual inspection through product recognition, color and shape of the materials for the plastic being sorted. Many of the American companies make their products in specific plastic shapes and color therefore making it easy to sort and recycle their plastics from the waste stream.
Floating mechanism is increasingly being employed by different recycling plants to separate high and low density plastics depending on weight characteristics (Harper, (2006).
Besides, the separating centrifuge is also employed to separate the plastics on the basis of their weight on the high speed rotating drums. According to Nigel (2004), physical sorting process is cost effective in that there is minimal capital investment as the method uses staff and low cost investment machines to sort out the plastics.
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Unlike in the automated method, there is no need of highly skilled manpower and technology in the process thereby reducing the cost of operation with a great margin. The method is highly suitable for small scale recycling process where the quantity of the plastic to be separated is generally low. However, this method can lead to inaccurate identification and separation due to human error. Types and the speed of separation in the process are highly limited since human beings employ only one visual mode in the identification process.
Besides, complications arise when different companies use similar shapes for packaging their products thereby creating confusion and making the company’s objective to recycle it’s plastics be highly compromised. To add to that, the process is highly manual requiring a lot of staff for effective completion which greatly reduces the ability and therefore ineficiency to sort the plastics (Tietenberg & Henk, 2006).
Plunket (2005) argues that, physical method of sorting plastics is highly uneconomical especially for separating large scale quantities of plastics due to the requirements of large staff numbers at any moment.
The quantity of plastics that can be sorted at any moment using the physical method is very limited compared to the automated method. Due to the above inefficiencies, the amount of plastics sorted and recycled is low and therefore not cost effective for recycling companies or the municipal authorities who have large quantities of plastics to be separated. Besides, the method do not guarantee the efficiency required for different plastics to effectively be sorted out. This inefficiency may compromise the products made from the recycled materials at the end of the process (Harper, 2006).
Automated sorting method This method employs various auto-separation systems which use sensors in establishing the chemical as well as the physical properties of the plastics to be separated (Tietenberg & Henk, 2006).
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Use of x-rays method of automated separation involves employing the radiation which detects the chlorine elements that are found in the Polyvinyl Chlorides (PVC).
This method is highly effective for the plastics that contain PVC but limited in application since it cannot be applied on other plastics.
Then, the modern infrared method analysis is being applied on a large scale basis to detect as well as separate plastics of multiple characteristics in their composition. Infrared rays are quantified and categorized on the basis of the characteristics of the specific plastic element type that is needed from the waste stream (Myer, 2007).
To add to that, optical scanning is also being used by different industries all over the world where the plastics are separated on the basis of their pigment coloration.
It ensures uniformity in the separation process and increases efficiency in the specific separation processes. Automated separation methods have also been effectively applied to separate general plastics from the waste mainstream depending on their main or individual characteristics like High Density Polythrene, Pollythylene Telephthalate and Polypropane. The main advantage of this method is that it is highly effective and the quantities of the plastics that can be sorted at any one moment is very high.
Myer (2007) notes that, different types of plastics are also easily recycled as the machine error is highly reduced compared to the high human error in the mechanical system. Also, the method is less labor intensive as it employs the modern technology in enhancing efficiency of the work done. However, the method requires high capital investment to install and operationalize the whole system. Protective equipments for the radiations add to the external costs for the people who work and operate the machines.
Infrared and x-ray generating machines require specialized experts to operate thus increasing the overhead cost to a very large extent. Besides, there are high hazard risk levels for the people operating with these machines due to exposure on the dangerous radiations of x-rays and high infrared levels (Nigel, 2004).
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Though the initial cost of machines installation is relatively high, this method is highly cost-effective in the 21st century due to the increasing need for faster plastic sorting and recycling. It is a great tool for conserving the environment and maximizing the resources utility.
The quantity of the plastics that can be sorted out at any moment being very high, then the method ensures that the remaining process and eventual processing into finished products receives enough and correct materials. Conclusion. Sorting as indicated earlier, is one of the most important steps in the recycling process as it makes the remaining processes easier and more effective in their application. It captures the plastic materials either from an integrated mixture in the waste stream or from assorted plastic mixtures therefore making it possible to use the material for further other products development.
Automated method is thus more cost effective in sorting the plastics due to it’s high efficiency in dealing with bulk wastes at any particular moment. As the world consumption patters continue changing year after year, the levels of the plastic wastes are bound to increase in the environment and the most cost effective method of sorting this waste should be adopted (Plunket, 2005).
Automated method should be adopted by all the municipal authorities, recycling commercial industries and individual industries which recycle their own wastes as it ensures long term cost effectiveness.