Rapid population and economic growth, have already consumed the available natural resources. To meet huge demand as well as to provide cheap products plastics has emerged as an alternative source. It has become the most common material since the beginning of the 20th century and modern life is unthinkable without it. The top biggest plastics producer and exporting countries in the world are China, Germany, U.S., Japan and France respectively wherein only China produces (23.9%). Wherein, the per capita plastic consumption is 109, 70, 65, 45, and 32 kg/year in U.S., Japan, E.U., China and Brazil subsequently. Contrary, global plastic production has increased from 1.5 Mt to 288 Mt between 1950 and 2012. At present total consumption of polymers including imported polymers (from Middle East Countries) and recycled plastic wastes (PWs) is 0.75 Mt in FY 2010- 2011. There are currently 3000 plastic manufacturing units in Bangladesh while per capita consumption is (5-8) kg/year against the world average 30. Plastics are used for different purposes viz. household products, toys, electric products, packaging materials, construction, transport, and plastic bags manufacturing. Unfortunately, what makes it so useful, such as its durability, light weight and low cost, also makes it problematic when it comes to its end of life phase turns into PWs. Roughly (33%) of the plastic products are in single use and thrown away which easily get mixed with municipal solid wastes (MSWs). PWs contribute into MSWs streams (5.10-12.3) % which varies from region to region. But they are not biodegradable in natural way with MSW rather it seems immortal, so it retards in decomposition of MSW.
Contrary, all plastic products life span is (1-30) years while it’s just a few second to 2/3 years for plastic packaging materials and plastic bags then they are thrown away after being used once. Besides, plastic is man-made long chain polymeric molecules and the basic elements are carbon, silicon, hydrogen, nitrogen, oxygen and chloride wherein conventional raw materials are petrol, diesel, coal and natural gas. For giving required appearance, strength, pigments, fillers, UV stabilizers, and flame retardants some commonly used additives (heavy metals) are Pb, Cd, Cr, Hg, Br, Sn and Sb. These additives are added to plastic materials although encapsulated in polymer matrix but not chemically bound to polymer molecules. Consequently, it can gradually be released (leached) into environment over the service life of a plastic made object or product, ultimate destination of these heavy metals are environment and human body through different ways. The most widely used plastic types in plastic products are PE, HDPE, LDPE, LLDPE, PVC, PET, PP, PS, ABS, PUR, and Nylon (PA) etc. All types of plastics remain unchanged in conventional dumping sites and sanitary landfill for thousands years. Besides, PVC contains Cl which is responsible of producing toxic chemicals viz. dioxin and furans during incineration. Therefore, developed countries are searching for alternate technology for PWs treatment.
However, Bangladesh generates 3, 36,000 tons/year of PWs wherein around 17,000 tons/year is going to the landfill. Among all types of PWs plastic bottles recycling (primary recycling) for plastic resin or plates recovery has already got popularity in Bangladesh. Currently, about (80-90) % plastic bottles are recycled in Dhaka city and other major cities viz. Chittagong, Rajshahi and Khulna etc. Then recycled PWs are used either for producing low quality plastic products in Bangladesh or exported in industrialized countries. By recycling PWs and some similar wastes only Dhaka city save BDT10,706 million annually. But they recycle all PWs in unhygienic environment and aren’t conscious about associated hazards with it too. Among all industrialized countries only China imports about (56%) PWs from the world traded. Contrary, all types’ of PWs have high heating value (20-46) MJ/kg almost equal to conventional fuel. However, only (8%) of PWs is recycled in the US, (15%) in Western Europe, but much less in developing countries. By utilizing high heating value, European countries, Japan and U.S. are generating electricity through thermal treatment (incineration). Thus it facilitates to reduce pollution as well as act a sustainable source of energy. Currently, Bangladesh has a huge demand of electricity and fuel but government is failing to meet such need of large population. However, by using the daily produced PWs (5,115-11,762) MWh/day electricity can be generated through incineration. Contrary, 920,548 litre fuels can be collected by using daily generated PWs through pyrolysis in Bangladesh.
Many developed countries like Japan, U.S., and E.U. use incineration for thermal treatment of MSW with a view to energy recovery. They have found plastic wastes are a major source of pollutants release into environment during incineration. In that case pyrolysis can be used for both energy recovery and fuel collection from PWs. Besides, pyrolysis is closed process, so there is no chance to release pollutants into atmosphere. Finally, I think thermal treatment (pyrolysis) of PWs is a sustainable solution for environment as well alternative source of energy in Bangladesh.
Author:
Ohidul Alam
Institute of Waste Treatment and Reclamation (IWTR), College of Environmental Science and Engineering, Tongji University, Shanghai 200092, P.R. China