Treatment of Plastic Wastes: An Innovative Solution

Rapid population increase and economic growth have already consumed the available natural resources. To meet huge consumer demand, as well as to provide cheap products, plastics have emerged as an alternative source.

Plastics, usually organic polymers, have become the most common manufacturing materials since the beginning of the 20th century and modern life is unthinkable without them.

The top plastics producers and exporting countries are China, Germany, USA, Japan and France respectively, with China alone producing 23.9 percent. Global plastic production has increased from 1.5 metric tons (MT) to 288 MT between 1950 and 2012.

Annual plastic consumption per capita (in kilogrammes) is 109, 70, 65, 45, and 32 in US, Japan, EU, China and Brazil respectively.

In Bangladesh, the per capita consumption of plastics, including imported polymers (mostly from the Middle East) and recycled plastic wastes (PW), is 5-8 kg per year, against the world average of 30kg/ year.

There are currently 3,000 plastic manufacturing units in the country. Plastics are used for different purposes, especially for making household items, toys, electronic products and packaging material, and in construction and transport sectors.

Unfortunately, what makes plastic useful, such as its durability, light weight and low cost, also makes it problematic when it comes to recycling or decomposing. Roughly, 33 percent of plastic products are used once only and thrown away, which easily get mixed with household garbage, or municipal solid wastes (MSW). Plastic wastes contribute to 5.10 to 12.3 percent of MSWs, which varies from region to region. But plastics do not biodegrade naturally, rather they seem indestructible.
The life span of most plastic products is 1 to 30 years, while it is just a few seconds to 2-3 years for plastic bags and packaging materials that   are thrown away after one-time use.

Plastic is man-made long chain polymeric molecules, derived from raw materials such as petroleum, coal and natural gas, with carbon, silicon, hydrogen, nitrogen, oxygen and chloride as basic elements.
For the required appearance, strength, colour, UV stabilizer and flame-resistance, heavy metals such as lead, mercury, tin, chromium, cadmium, bromine and antimony. These toxic additives are added to plastic encapsulated in polymer matrix, but not chemically bound to the polymer molecules. Consequently, the metals can gradually be released into the environment over the life cycle of a plastic object or product, ultimately ending up in the human body in various ways.

All types of plastics remain unchanged in conventional dumping sites and landfills for thousands years. The most widely used plastics are PVC, PET, nylon, etc. For example, PVC contains chlorine which is produces toxic chemicals, namely dioxins and furans when burned. Therefore, developed countries are searching for alternative technology for PW treatment.

Meantime, Bangladesh generates 336,000 tons/year of plastic wastes, wherein around 17,000 tons go to landfills. Among all types of PWs, plastic bottle recycling to obtain plastic resin has already gained popularity in the country.

Currently, about 80-90 percent of plastic bottles are recycled in Dhaka and other major cities like Chittagong, Rajshahi and Khulna. The recycled plastics are used either for producing low-quality products or exported in industrialised countries.

By recycling plastic and similar wastes Dhaka city saves Tk 10,706 million annually. However, the recycling is usually done in unhygienic conditions, with total disregard for the associated hazards.

Among all industrialized countries, only China imports about 56percent of PWs from around the world. However, only 8 percent of PWs is recycled in the US, 15 percent in Western Europe, and much less in other developing countries.

All types of PWs have high heating value (20-46 megajoules/kg), which is almost equal to conventional fuel. By utilizing the heating capacity, European nations, the US and Japan are generating electricity through thermal treatment, or pyrolysis. Thus, helping to reduce pollution as well as providing a sustainable source of energy.

Currently, Bangladesh has a huge demand for electricity and fuel which remains largely unmet. However, by using the daily produced PWs, 5,115-11,76 MWh/day electricity can be generated through incineration. On the other hand, 920,548 litre fuel can be obtained from daily generated PWs through pyrolysis.   

Many developed countries like Japan, US, and EU use incineration for thermal treatment of solid wastes with a view to energy recovery. They have found plastic wastes to be a major source of pollutant when released into the environment during incineration.
Pyrolysis can be used for both energy recovery and fuel collection from PWs. Besides, it is a closed process, so there is no chance to release pollutants into the atmosphere.
Finally, I think thermal treatment of PWs is a sustainable solution for the environment as well alternative source of energy in Bangladesh.