*Waste Material Recycling in the Circular Economy - Challenges and Developments*

**Figure 4.** *Drying of sorted waste.*

monomers [44]. Major research is being carried out on the chemical recycling of the world's biggest plastic waste from PE and the results have been impressive and when concluded will help to reduce the menace associated with PE disposal. Ha'jekova and his colleagues investigated the recycling of LDPE using co-pyrolysis with

#### *Polyethylenes: A Vital Recyclable Polymer DOI: http://dx.doi.org/10.5772/intechopen.102836*

naphtha at the temperature range of 740°C -820°C and found a high yield of alkenes as its primary products and coke [45].

The energy recovery process is the fourth method of polyethylene recycling, also known as quaternary recycling. This is the recovery of the plastic's energy content on the application of external heat. Incineration is an energy recovery method that reduces a large volume of organic materials in an enclosed system. This method generates a high amount of energy from the polyethylene fed inside the incinerator but poses a higher health risk due to the high production of toxic substances that are carcinogenic to human health.

## **5.2 Plastic composting**

This is the breakdown of waste plastics into small natural substances such as carbon dioxide, water, and methane by microorganisms. Composting can be done through aerobic or anaerobic methods. Aerobic composting is the breakdown of the polyethylene wastes by microorganisms in the presence of oxygen or air, while anaerobic composting is the decomposition or degradation of plastic waste substances by microorganisms in the absence of oxygen. Generally, microorganisms bind themselves to the plastics' surface, colonize the exposed surface, catalyze enzymatic degradation of the plastic into lower molecular weight monomers, dimers, and oligomers, and finally form carbon dioxide and water as its bye products [46]. Some of the microorganisms that biodegrade polyethylene include, Acinetobacter sp., Ideonella sakaiensis, Bacillus sp., Staphylococcus sp., Streptococcus sp., Diplococcus sp., Micrococcus sp., Pseudomonas sp., and Moraxella sp. ss bacteria and, *Aspergillus niger*, *A. ornatus*, *A. cremeus*, *A. flavus*, *A. candidus*, *A. ochraceus, A. nidulans*, and *A. Glaucus* as fungi [47].
