Author – Sourav Daspatnaik
Rapid population growth, urbanization, and industrial growth have led to severe waste management problems in cities around the world. Simultaneous development in economic prosperity and industrialization often conflict with sound environmental considerations. Globally, nearly 140 million tons of plastics are produced each year. In India, around 4-5% of municipal solid waste (MSW) material are post-consumer plastics in comparison to 6-10% in the US, Europe and other developed countries. India recycled 47% of its total plastic waste in contrast to China (11%), the US (3.5%), South Africa (15%), and UK (7%). There are around 20,000 plastics recycling industries in India with a daily capacity of 1,500 tons.
The easiest way to reduce the volume of solid waste is to burn it in a process called ‘incineration’. The basic advantages of a municipal waste incinerator are that they require less land and also be effectively used for energy generation. However, incineration of plastics in MSW also generates toxic gas emissions that contain heavy metals, dioxins, and other volatile organic compounds (VOCs). Heavy metals viz. zinc, cadmium, arsenic, lead, and mercury are parts of the waste stream and therefore, when incinerated, they reach the atmosphere and also persist with soot particles and generated ash.
The energy content of MSW depends on its composition as well as its moisture content. Plastics have a high calorific value since they are derived from petrochemical sources (36,500 kJ/kg) and they are very much comparable with coal (28,500 kJ/kg) and fossil fuel (42,500 kJ/kg). On an average, the production of plastic uses 5% of the world’s oil as feedstock compared to 85% used for heating and transport. Most of this energy is recoverable in the form of heat, which can then be converted to electricity.
In order to reduce the plastic waste management problem, we need to adopt the principles of waste prevention. The use of durable plastics need not be reduced, but we need to promote judicious use and reuse of single-use plastics. If plastic compounds are made more durable and if the general perception of consumers regarding the reuse of plastic and reduced disposal is changed, then the waste plastic problem can be sorted out. However, there are several constraints for proper plastic waste management in India such as proper collection, segregation, and transportation of the discarded plastic material. Increase in public awareness coupled with changes in individual behavior can be an effective way to reduce the environmental repercussions of waste plastics.
Plastic waste recycling technologies
The different types of technologies used for recycling plastic waste are:
Substitution of primary fuel
Raw material substitution offers advantages for cement industry as well as for Municipal Authorities responsible for waste management. By co-processing of plastic waste with primary fuel, cement producers or power plants can save fossil fuel and raw material consumption, contributing to more energy-efficient production. A major advantage of this recovery method is by using an existing facility, the need to invest on other plastic waste processing or to secure land filling is eliminated.
Liquid refuse-derived fuel conversion
Conversion of plastic waste into liquid refuse-derived fuel (RDF) oil through catalytic pyrolysis whereby it is segregated mechanically from solid waste and processed. This separation method is not fool-proof, other lighter waste material is also segregated along with plastic waste. Then the segregated waste is sent through a conveyor belt fixed with optical segregation device for 100% source segregation of plastic waste. This mixed plastic waste is converted into a useful fuel, i.e. liquid RDF oil through catalytic pyrolysis. The entire feed material is converted into Liquid RDF, gases and some sludge. There is no effluent generated in the process and the unused gases from the reactor are released through chimneys.
Plasma Pyrolysis is a state-of-the-art technology that integrates the thermo-chemical properties of plasma along with the pyrolysis process. Plasma pyrolysis is the thermal disintegration of any carbonaceous material in an oxygen-starved atmosphere. When optimized, the most likely compounds formed are methane, carbon monoxide, hydrogen, carbon dioxide and water vapor. The process conditions are maintained such that it eliminates any possibility of formation of toxic dioxins and furans (in case of chlorinated waste). The conversion of organic waste into non-toxic gases is more than 99%. The extreme conditions of plasma kill stable bacteria and the pyrolysis process helps reduce carbon dioxide emissions and landfills.
Gasification of waste plastic
This is another way to reduce landfill space and incineration costs of waste plastic. The gasification process’ main advantage is that it uses inert air containing nitrogen instead of oxygen, making it a simpler process and also reduce the cost. This is a vertical fixed bed gasification system, where a thermo-chemical process converts carbon-based material into gases such as carbon dioxide, carbon monoxide, and hydrogen and methane gas, which can be used for heat or power generation.
Gasification technique using air as a gasifying agent has proven to be an eco-friendly way of converting biomass and plastic waste refuse into fuel gases. Direct gasification has advantages of simple technique and cost-effective operation, but the presence of nitrogen in the inert air could reduce the calorific value of resulting fuel gases due to dilution. Waste plastic includes polyethylene, polypropylene and polystyrene, which are softened by a heat process to 100-150 degrees C.
Innovations in plastic recycling include increasingly reliable chemical detectors and sophisticated software that collectively increase the accuracy and productivity of automatic sorting. The recycling process uses minimal water to recycle the plastic, where water is used only as a coolant. The water-less method results in recycled plastic pellets that are better than others, which can be useful in the construction of roads.
Recommendations for plastic waste management in India
Some of the recommendations to improve the existing MSW practices in India:
• Community participation in SWM is the key to sustain a project related to the management of solid waste. A waste generator fee is the best way forward
• It is important to achieve near-source waste segregation as biodegradables and recyclable material for proper waste management
• Viable decentralized composting plants to be installed to reduce the load on garbage collectors. For large cities, zone-wise decentralized composting units should be setup
• Encourage educational institutions to take up waste management in their curriculum and create student projects for waste recycling
• Waste to be treated as a resource and a formal recycling sector to be developed from the waste thereby providing employment to rag-pickers and absorb them in the mainstream.
• Manufacture of non-recyclable single-use polyethylene bags should be banned or research should be initiated to develop biodegradable bags.
• Use of innovative and proven technologies like plastic-to-fuel and waste-to-energy must be encouraged with special provisions for buyback.
• Practices of leachate/liquid biodegradable waste recirculation in landfills should be encouraged to enhance waste stabilization and gas recovery as practiced in developed countries.
• Protection of groundwater contamination from leachate percolation from open dump/landfill site should be made compulsory.
Sourav Daspatnaik is the CEO, Swach Environment Pvt Ltd. and is also an independent director in several other companies and mentors social enterprises on clean technologies.