Recycling of waste plastics – To be done in an environment-friendly manner:

Recycling of waste plastics – To be done in an environment-friendly manner:

We find considerable growth in use of plastic everywhere due to the beneficial properties of plastics, such as: (a) Extreme versatility and ability to be tailored to meet very specific technical needs. (b) Lighter weight than competing materials, reducing fuel consumption during transportation. (c) Extreme durability. (d) Resistance to chemicals, water and impact. (e) Good safety and hygiene properties for food packaging. (f) Excellent thermal and electrical insulation properties. (g) Relatively inexpensive to produce.

However, plastics waste creates lot of nuisances and degrade environment in a big way. Recycling and re-utilization of waste plastics have several advantages. Recycling and re-utilization of waste plastics lead to a reduction of the use of virgin materials and of the use of energy, thus also a reduction of carbon dioxide emissions. Economically, in some cases, plastics recycling may be profitable. However, a number of factors can complicate the practice of plastics recycling, such as the collection of the plastics waste, separation of different types of plastics, cleaning of the waste and possible pollution of the plastics. A further complicating factor is the low-value nature of most of the products that can be manufactured from recycled plastics. Reusing plastic is preferable to recycling as it uses less energy and fewer resources.

A. It has been observed, to reduce bad effects of waste plastics, it is better to recycle and re-utilize waste plastics in environment-friendly manners. As per statistics, about 80% of post-consumer plastic waste is sent to landfill, 8% is incinerated and only 7% is recycled. In addition to reducing the amount of plastics waste requiring disposal, recycling plastic can have several other advantages, such as:

(a) Conservation of non-renewable fossil fuels - Plastic production uses 8% of the world's oil production, 4% as feedstock and 4% during manufacture.

(b) Reduced consumption of energy.

(c) Reduced amounts of solid waste going to landfill.

(d) Reduced emissions of carbon-dioxide (CO2), nitrogen-oxides (NOx) and sulfur-dioxide (SO2).

B. There are about 50 different groups of plastics, with hundreds of different varieties. All types of plastic are recyclable. To make sorting and thus recycling easier, the American Society of Plastics Industry developed a standard marking code to help consumers identify and sort the main types of plastic. Before recycling, plastics are sorted according to their resin identification code.The type of plastics (as per the resin identification code) and their most common uses are given below:

Type (Resin identification code)	Plastics	Common uses
1	PET	Polyethylene terephthalate - Fizzy drink bottles and oven-ready meal trays.
2	HDPE	High-density polyethylene - Bottles for milk and washing-up liquids.
3	PVC	Polyvinyl chloride - Food trays, cling film, bottles for squash, mineral water and shampoo.
4	LDPE	Low density polyethylene - Carrier bags and bin liners.
5	PP	Polypropylene - Margarine tubs, microwaveable meal trays.
6	PS	Polystyrene - Yoghurt pots, foam meat or fish trays, hamburger boxes and egg cartons, vending cups, plastic cutlery, protective packaging for electronic goods and toys.
7	OTHER	Any other plastics that do not fall into any of the above categories. - An example is melamine, which is often used in plastic plates and cups.

C. Plastic process scrap recycling - Currently most plastic recycling in of the developed countries are of 'process scrap' from industry, i.e. polymers left over from the production of plastics. This is relatively simple and economical to recycle, as there is a regular and reliable source and the material is relatively uncontaminated. This is usually described as reprocessing rather than recycling.

D. Post-use plastic recycling - Post-use plastic can be described as plastic material arising from products that have undergone a first full service life prior to being recovered. Households are the biggest source of plastic waste, but recycling household plastics presents a number of challenges. One of these relates to collection.

E. Mechanical recycling - Mechanical recycling of plastics refers to processes which involve the melting, shredding or granulation of waste plastics. Plastics must be sorted prior to mechanical recycling. Mostly, sorting is done manually. Recently, technology is being introduced to sort plastics automatically, using various techniques such as X-ray fluorescence, infrared and near infrared spectroscopy, electrostatics and flotation. Following sorting, the plastic is either melted down directly and molded into a new shape, or melted down after being shredded into flakes and than processed into granules called re-granulate.

F. Chemical or feedstock recycling - Feedstock recycling describes a range of plastic recovery techniques to make plastics, which break down polymers into their constituent monomers, which in turn can be used again in refineries, or petrochemical and chemical production. A range of feedstock recycling technologies is currently being explored. These include:

(a) Pyrolysis,

(b) Hydrogenation,

(c) Gasification and

(d) Thermal cracking.

Feedstock recycling has a greater flexibility over composition and is more tolerant to impurities than mechanical recycling, although it is capital intensive and requires very large quantities of used plastic for reprocessing to be economically viable.

G. Lots of innovations in recycling of waste plastics have been introduced in many countries. We have to see, we should not pollute environment while going for recycling and use of recycled products.

Bacteria that effectively transform plastic waste into a useful eco-friendly plastic:

Bacteria that effectively transform plastic waste into a useful eco-friendly plastic:

In response to problems associated with plastic waste and its effect on the environment, there has been considerable interest in the development and production of biodegradable plastics. Innumerable amount of research have also been conducted world wide to find out ways to convert synthetic plastic waste into biodegradable and compostable material. Their effort was to isolate bacterium that can effectively convert a waste plastic product into safe, biodegradable product or to make safe and biodegradable plastic, which can be used safely for further manufacture of some product.

A. It has been observed that, chemicals called Polyhydroxyalkanoates (PHAs) are polyesters that accumulate as inclusions in a wide variety of bacteria. These bacterial polymers have properties ranging from stiff and brittle plastics to rubber-like materials. Because of their inherent biodegradability, PHAs are regarded as an attractive source of nonpolluting plastics and elastomers that can be used for specialty and commodity products. They were the first biodegradable polyesters to be utilised in plastics. These aliphatic polyesters naturally produced via a microbial process on sugar-based medium. The two main members of the PHA family are polyhydroxybutyrate (PHB) and polyhydroxyvalerate (PHV).

B. There is good news that, recently some European scientists have discovered a bacterial strain that uses styrene, a toxic byproduct of the polystyrene industry, as fuel to make Polyhydroxyalkanoate (PHA) - biodegradable plastic. The microbes, a special strain of the soil bacterium Pseudomonas putida, convert polystyrene foam — commonly known as Styrofoam — into PHA, a biodegradable plastic. This is among the first to investigate the possibility of converting a petroleum-based plastic waste into a reusable biodegradable form.

Researchers utilized pyrolysis, a process that transforms plastic waste materials by heating them in the absence of oxygen, to convert polystyrene — the key component of many disposable products — into styrene oil. The researchers then supplied this oil to Pseudomonas putida, a bacterium that can feed on styrene, which converted the oil into PHA. The process might also be used to convert other types of discarded plastics into PHA.

C. PHA has numerous applications in medicine and can be used to make plastic kitchenware, packaging film and other disposable items as well. This biodegradable plastic is resistant to hot liquids, greases and oils, and can have a long shelf life. The advantageous side of PHA is unlike polystyrene, it readily breaks down in soil, water, septic systems and backyard composts. In other words, it is biodegradable and compostable.

D. Worldwide, more than 14 million metric tons of polystyrene are produced annually, most of this ends up in landfills producing pollution. Thus, this system can help transform plastic waste into a useful eco-friendly plastic, significantly reducing the environmental impact of this ubiquitous, but difficult-to-recycle waste stream.