Plastic pollute beaches & oceans.
Plastic bags litter the landscape.
Plastic bags kill animals.
During product manufacturing various types of gases are
released.
Indiscriminate plastic waste disposal on land makes the land
infertile due to its impervious nature.
Burning of plastics generates toxic emissions such as Carbon
Monoxide, Chlorine, Hydrochloric Acid, Dioxin, Furans, Amines,
Nitrides, Styrene, Benzene, 1, 3- butadiene, CCl4, and
Acetaldehyde.
Sub-standard plastic bags, films etc. pose problem in
collection and recycling.
Littered plastics give unaesthetic look and choke the drain.
Garbage mixed with plastics interferes in waste processing
facilities and also cause problems in landfill operations.
Lead and Cadmium pigments, commonly used in LDPE,
HDPE and PP as additives are toxic and are known to leach
out.
Non-recyclable plastic wastes poses disposal problem.
Recycling of plastics through environmentally
sound manner
Plastics recycling technologies have been historically divided into
four general types- primary, secondary, tertiary and quaternary.
Steps Involved in the Recycling Process:
Selection: The recyclers/reprocessors have to select the waste
/scrap which are suitable for recycling/ reprocessing.
Segregation: The plastics waste shall be segregated as per the
codes mentioned in the BiS guidelines.
Processing: After selection and segregation of the preconsumer
waste (factory waste) shall be directly recycled. The post
consumer waste (used plastic waste) shall be washed, shredded,
agglomerated, extruded and granulated.
Mechanical recycling refers to operations that aim to recover plastics
waste via mechanical pro-cesses (grinding, washing, separating, drying,
re-granulating and compounding), thus producing recyclates that can be
converted into new plastics products, often substituting virgin plastics.
For mechanical recycling only thermoplastic materials are of interest,
i.e. polymeric materials that may be re-melted and re-processed into
products via techniques such as injection moulding or extrusion.
Thermosets cannot be reprocessed in this way but may be chemically
recycled back to feedstock or used as a carrier (e.g. cement kilns).
Thermoplastics represent a variety of multiple polymers with different
physical and mechanical properties. A major hurdle for mechanical
recycling is that these different polymers are generally non-miscible or
compatible with each other. This means that a mixture of different
polymers can have inferior mechanical properties which make the
recyclates unsuitable for many applications. Consequently, the
mechanical recycling of plastics waste is generally only feasible for
homogene-ous, single polymer streams or for defined mixtures of
polymers that can be effectively separated into the individual polymers.
Mechanical recycling of plastic waste is the simplest and relatively cheap recycling
method.
The steps of mechanical recycling are as follows:
Cutting
Large plastic parts are cut by saw or shears for further processing.
Shredding
Plasics are chopped into small flakes.
Contaminants separation
Contaminants (e.g. paper) are separated from plastic in cyclon separators.
Floating
Different types of plastics are separated in a floating tank accrding to their density.
The flakes are also washed and dried.
Extrusion
The flakes are fed into an extruder where they are heated to melting state and
forced through the die converting into a continuous polymer product (strand).
Pelletizing
The strands are cooled by water and cut into pellets, which may be used for new
polymer products manufacturing.
Chemical or feedstock recycling is a processes, in which a plastic
polymer is broken down into its constituents - monomers. This process is
called depolymerization. The monomers may be then used as raw
material for manufacturing a new polymer. Chemical recycling (feedstock
recycling) is more expensive than mechanical recycling.
There is a range of chemical recycling methods:
Pyrolysis - chemical decomposition of polymers induced by heat in the
absence of oxygen.
Polyethylene Terephtalate (PET) may be converted into dimethyl
terephthalate and ethylene glycol, which are used as additives to the
virgin raw materials in PET production.
Hydrogenation - chemical reaction with Hydrogen (H2).
Gasification - conversion of polymers into a mixture of carbon monoxide
(CO) and hydrogen.
Energy recovery
Plastics store energy, which may be
recovered by various ways:
Municipal incineration in energy-from-waste
incinerators (Combustion). The heat of
plastic waste burnt at high temperature is
used for production electricity or steam.
Production of alternative fuels from plastic
waste (Pyrolysis and Gasification). The fuel is
used in various manufacturing processes and
in power stations.
Landfilling
Landfill is the conventional approach to waste
management, but space for landfills is becoming scarce in
some countries.
A well-managed landfill site results in limited immediate
environmental harm beyond the impacts of collection and
transport, although there are long-term risks of
contamination of soils and groundwater by some additives
and breakdown by products in plastics, which can become
persistent organic pollutants.
A major drawback to landfills from a sustainability aspect
is that none of the material resources used to produce the
plastic is recovered.
Incineration
Incineration reduces the need for landfill of plastics waste,
however, there are concerns that hazardous substances
may be released into the atmosphere in the process.
Incineration can be used with recovery of some of the
energy content in the plastic.
The useful energy recovered can vary considerably
depending on whether it is used for electricity generation,
combined heat and power, or as solid refuse fuel for co-
fuelling of blast furnaces or cement kilns.
Polymer Blended Bitumen Road
A brief description of the technique used in laying road
using plastic waste is given in figure.
Co-processing of Plastic waste in Cement Kiln
Co-processing of plastic waste as Alternative Fuel and
Raw Material (AFR).
Co-processing indicate substitution of primary fuel and raw
material by waste.
Waste material such as plastic waste used for co-processing are
referred to as alternative fuels and raw material (AFR).
One of the advantage of recovery method used in existing facility
is eliminating the need to invest on other plastic waste practices
and to secure land filling.
Plasma Pyrolysis Technology (PPT)
Pyrolysis is the thermal disintegration of carbonaceous
material in oxygen-starved atmosphere.
The intense and versatile heat generation capabilities of
Plasma Pyrolysis technology enable it to dispose of all
types of plastic waste including polymeric, biomedical and
hazardous waste in a safe and reliable manner.
When optimized, the most likely compounds formed are
methane, carbon monoxide, hydrogen carbon dioxide and
water molecules.
Conversion of Plastics Waste into liquid fuel
The entire process is undertaken in closed reactor vessel
followed by condensation, if required.
Waste plastics while heating upto 2700 to 3000 C convert
into liquid-vapour state, which is collected in condensation
chamber in the form of liquid fuel.
The tarry liquid waste is topped-down from the heating
reactor vessel.
The organic gas is generated which can be used in dual
fuel diesel generator set for generation of electricity.
Figure 2: Schematic flow diagram of process.
Plastic Waste Management has assumed great significance
in view of the urbanisation activities.
Various strategies are being devised to mitigate the impact
of plastic waste in India.
Some significant challenges still exist from both
technological factors and from economic or social
behaviour issues relating to the collection of recyclable
wastes, and substitution for virgin material.
