Analytical Reviews Ecology WHAT PEOPLE HAVE TO DO WITH POLYMERIC WASTE|
people have to do with polymeric waste
20th century is characterized not only by impressive achievements in
nuclear physics and molecular biology and a breakthrough of a man in outer space,
but also by the intensive commercial production of new synthetic polymer-based
materials which had never existed on the Earth before. The excellent properties
of these new materials let them penetrate in all spheres of human life; now they
are completely irreplaceable and absolutely necessary for people. However,
together with intrinsic outstanding positive qualities, synthetic polymers have
a significant disadvantage: unlike many natural materials, they, having worked
out their resource and functions, are not quickly decomposed under the influence
of the environment aggressive factors as light, heat, atmosphere gases,
microorganisms and continue to exist in the form of a long-living waste,
inflicting an irreparable damage to the nature. Numerous cases of a death of
rare sea animals, for instance, giant sea turtles which swallow plastic bags
floating on the sea surface mixed them up with medusas, their food, are known.
People have to help the nature:
as though namely people manufacture polymeric materials to satisfy their needs,
they also have to protect the nature from a negative influence of synthetic
materials. However, polymeric waste utilization process is not simpler and
cheaper than the polymer production process. People so far prefer to choose the
simplest way: they stock these waste together with other rubbish on the
Earth’s surface and thus produce another magnificent hand-made creation, a
dump. At present, each man annually generates about 200 kg (700 kg in the USA)
of waste products, out of which 10% to 15% are polymers. A share of polymeric
waste is increasingly growing. If people continue to dispose waste to dumps,
they will create a principally new landscape: all big settlements will be
surrounded with an uninterrupted ring swell of buried waste. As a width of the
swell is permanently growing, the swell will roll on cities, fields, meadows,
forests and even break in the seas and oceans. Growth rate of a dump size in
developed countries exceeds the population growth rate. While the world
population is annually increased by 1.5-2.0%, the size of waste dumps rises by
6%. Waste products accumulated in dumps are gradually decomposing and poison the
environment with decomposition products. Yet polymers are more or less inert
components of rubbish, they are step by step decomposing and release substances,
including super-toxic compounds of dioxin and furan range, which are hazardous
to living beings. Therefore, to continue using of polymeric material growing
volumes, mankind have urgently develop effective methods of polymeric materials
utilization and disposal.
Let’s consider current
situation in this field. Since polymeric materials are rather expensive,
polymeric waste are considered as valuable products, subject to material
recycling, i.e. to treatment with further production of: 1) original polymers,
fillers, armoring elements 2) monomers 3) other chemical compounds suitable for
first recycling method seems the most promising but difficult to be implemented.
Even though polymeric wastes are carefully separated from other rubbish, it’s
practically impossible to process the polymeric wastes and turn them into a
polymeric recycle product with satisfactory properties due to an intrinsic
feature of polymers, namely, their inability to mix with each other or, in
scientific terms, their thermodynamic incompatibility. Upon mixing of polymers
with even a similar chemical nature (for instance, polyethylene and
polypropylene), two-phase dispersed systems with the properties much more worse
than those of the original compounds are formed. So, before processing polymeric
wastes, packages, for instance, through melting in granules, suitable for
casting of new polymeric products, careful sorting of wastes by their chemical
composition is required. For example, in processing polyetheleneterftalate
bottles, a number of polyvilylchloride bottles shouldn’t exceed 500 bottles
per million. It’s clear that this result can only be obtained through an
exhausting manual sorting of bottles which, in addition, should be specially
marked. Otherwise, it’s impossible to sort them up only by their exterior.
Women from poor Philippine families are often involved in the bottle sorting
process; they gather and sell for processing various polymeric package thrown
onshore with the sea waves.
Sophisticated industrial polymer
sorting schemes, in which process of polymer separation is based on negligible
differences in physical and chemical properties of various polymers, are being
In one of these schemes, package
waste are crushed to small particles (a few millimeters in size), delivered to a
magnetic separation unit to remove ferrous metals and then to an electric
precipitator (operation principle is based on Foucault (eddy) current) to remove
nonferrous metals. To remove solvable contamination, washing process is then
used. After that, the following operations are performed one after another:
tossing, flotation (separation by density), and then electrostatic separation.
To effect more precise electrostatic separation, improved cartridge drum can be
used. The drum is made from a dielectric material and rotates on a
horizontally-installed shaft. An arc electrode (the circle arc angle is 150° )
is located inside the drum. Another electrode with a circle arc angle of 90° is
located outside the drum, with a big-end-down gap between the electrode and the
drum. Passing through the drum, polymer mixture is split into two fraction by
chemical composition, and one mixed fraction. Electrostatic separation is used
to separate thermoplastic from elastomers. The process goes on inclined surface,
on which rubber particles move abruptly, while thermoplastic particles slide
with a speed which depends on electric charge value, typical for each sort of
thermoplastic. Flotation in the presence of special surface-active substances
allows to effectively separate polyethylene and polyvilylchloride.
In automatic sorting system,
plastics are separated based on signal received from a sophisticated optic
device operable in infrared bands.
the above-mentioned difficulties in collecting and sorting polymers, in Germany
a tone of polyetheleneterftalate, a recycled product which is broadly used for
package production, costs DM 3,000, while a tone of the original polymer costs
only DM 1,600. According to the data of the German company RIGK, reprocessing of
polymeric wastes from economic and ecological point of view is feasible only if
the wastes are separated by sorts and if it’s possible to manufacture products
which are in high market demand. Since profitability of this industry seems
doubtful, European authorities took another way. They force polymer package
producers and consumers to get busy with the issue of proper package utilization
or destruction. The EU has adopted Directive 94/62/CE which stipulates the main
requirements on package in respect of negative impact on the environment. All
countries, producing package for Europe or in Europe, have to comply with this
standard to avoid rigid economic sanctions to be imposed. The EU member
countries, in turn, approved the statutes which regulate procedures of polymer
wastes collection, processing or destruction in these countries. For instance,
Decree 22/97 which allows to sell only the package meeting the European
standards has been adopted in Italy. Package producers and consumers on parity
basis have set up the National Package Consortium (CONAI) which coordinates
collection, sorting and transportation of materials, establishes general
conditions to return the wastes to the producers, and develops and adds programs
on package and wastes management. Similar bodies were established and
successfully operate in other European countries.
Given a drop in budget spending
on implementation of the ecology conservation measures in the USA, commercial
enterprises are recommended to strengthen information activity to assist
municipal authorities in organizing the process of wastes gathering by types.
The society should clearly know the final target of waste gathering. American
Society for Plastics is realizing a program of municipal polymer wastes
collection and utilization. Major attention is paid to selection of wastes
collectors and signing contracts with them, submission of convenient containers
to them, and organization of wastes transportation to the destination (processing
Germany’s government activity
is a good example of nature conservation. In 1993, this country allocated DM 60
bln to realize environmental protection programs; the stated figure is the
largest in the world. 956,000 people were occupied in this field in 1994. In
1998, a new law was adopted. The law drastically reduces the possibility of
burring the wastes in which organic components content exceeds 5%. The law is
effective since 2005. In Germany, the DSD system (Dual System Deutchland) which
functions similar to an ordinary municipal wastes gathering system is
implemented. The system unites about 600 leading companies involved in
manufacture consumer goods and appliances, furnish as well as in production of
polymer package (containers, package tape, film, inlays, etc.). The DSD system
organizes package collection and processing centers and equips plants. In 1997,
a new plant for polymer wastes processing was built. The plant uses industrial
and municipal wastes (films, containers, bottles, glasses, etc.) as a raw
material. The processing process includes preliminary sorting of package by
separate fractions: bottles and containers, films and glasses. These fractions
are separately washed and delivered to a mill where the wastes are wetly ground
to the size of about 15 mm. Then wastes are additionally treated from adhered
particles of paper, glue, wood, and mineral contamination as well. Purification
efficiency is very high. After that, a plastic mixture is directed to a
centrifuge and sorted by specific weight. The plant is capable to output up to
25 sorts of a highly treated (with efficiency of 99.9%) grained plastic. Upon
the consumers request, colorants, pigments, stabilizers, plasticizers and other
additives can be added to the grains. Despite rather high costs, volumes of
recycling polyetheleneterftalate rapidly grow. While in 1997, only 91,000 tones
of this polymer were utilized in Europe, in 2002 the figure is expected to rise
up to 300,000 tones, with the major share of the volume to be used for beer
20 European companies have
entered the utilization process. They plan to build 10 to 15 new plants for
polyetheleneterftalate secondary processing. Wide application of polymers for
polyvinylchloride window block construction have set a new target - utilization
of these window blocks after 20 years of their operation. 15 companies are
involved in manufacture of parts for these plastic window blocks, and 3,000
companies annually install about 12 mln window blocks. The results of a research
show that polyvinylchloride can be processed into granulate as many as 8 times
and addition of recycled products in original plastic doesn’t worsen the
properties of the latter. VEKA Umwelttechnick built a large plant to utilize old
polyvinylchloride window blocks and arranged the gathering of these blocks
across the country. Granulate is delivered to the window block manufacturers.
Germstmeier Recyclate outputs over 100 items, made from recycled materials, for
Porsche cars; the product range includes guides, supports, lids, etc. Materials
are selected depending on the purpose of a part and may include recycled
products made from polyamide, polypropylene, mixture of polycarbonate and
ABC-plastics, mixture of polypropylene and rubber. Recycled products processing
process is similar to the above-described process and has only minor
modifications in respect of technological parameters.
examples of successful plastics recycling are available.
Multiport Recycling has been
given an award for development and implementation of the technology for
production of cable channels laid along railroads in Germany and Switzerland.
Introduction of fireproofing compounds has allowed to significantly increase
fire-resistance of the items: there service life now is 30 years, but might be
increased up to 60-100 years. The said channels are of a half-cylinder design,
with flanges and a lid, which can withstand heavy loads.
Ford has mastered a manufacture
of air filter housings with application of polyamide recycled products which are
obtained in processing of a fluff of worn floor sheets. So far, about 3 mln
filters have been produced and no deviation in technology or problems in
operation have been registered.
In the USA, a new method of
recycling polystyrene and polystyrene foam has been developed in the USA. Under
this method, raw materials are dissolved, glutinous gel is formed and then
In Australia, a technological
process for production of a new polymeric material from polyethylene film cuts
and cellulose residues (60 to 80%) has been developed. This material allows to
produce items in extrusion and injection processes.
In 1996 in Austria, material
recycling of 38,000 tones of package saved 34,000 tones of original plastic and
38 mln liters of oil and reduced carbon dioxide emission to the atmosphere by
23,800 tones. Thermal recycling of additional 20.1 thousand tones of polymeric
wastes saved 15.7 mln liters of oil and cut emissions by 23,000 tones.
Ecological effect is considered
the top criteria of recycling efficiency.
Wastes of many polymeric
materials can be subjected to thermal recycling with consequent output of useful
non-polymeric products. Polyetheleneterftalate can be de-polymerized to the
origin materials, namely, ethylene glycol and terephtalic acid, with the
application of a “supercritical” water which effects as an acid catalyst.
Terephtalic acid is 100 percent separated at the temperature of 350-400° C,
ethylene glycol is separated with lower efficiency owing to passing of secondary
reactions. Under critical conditions, strong acids or bases are not required.
The process goes more or less rapidly and is economically-efficient enough.
Polyurethane wastes could be processed in a similar way.
Utilization of rather complex and
expensive products as worn tires is a crucial problem for all industrially
developed countries. The number of worn tires is huge. The USA, Europe and Japan
annually produce 4.3, up to 9 and 0.9 mln tones of worn tires, respectively. In
Russia, an automobile pool has reached 30 mln and a number of worn tires is also
Of all the applied tire
utilization methods, it’s necessary to mention the technology which provides
for crushing of tires to particles of some millimeters in size. The crushed
particles are used as an additive to road pavements and allow to improve
pavement frost resistance and to increase road traffic safety owing to better
coherence of car tires with a pavement. The process is rather energy intensive:
to crush a tone of tires, 800-1,500 kWh of electricity is required.
The second tire utilization
technology is a thermal decomposition (pyrolysis). Liquid fraction being formed
in pyrolysis process can be used as an additive to rubbers or plastics, while
solid fraction can be processed in activated carbon with a high adsorption
capability. This tire utilization method seems very attractive and promising,
since it enables to obtain useful product which are in short supply on the
market. However, it’s economic effectiveness and ecological safety should be
confirmed by pilot tests.
The third tire utilization
technology is use or tires as a fuel to generate heat and power.
of worn tires in regeneration products widely spread before is now proved
economically inefficient, and regenerate production process is suspended in many
countries of the world. Recent information on the possibility to break
vulcanized sulfuric cohesion nets in a rubber by means of microbiological method
with the use of the Sulfolobus bacteria encourages the advocates of this method.
Pilot bioreactor with the capacity of 200 liters daily processed at a room
temperature up to 32 kg of tires.
Owing to continuous rise in
nonrenewable organic fuel price, big expectations are laid on generation of
energy on plants where wastes, including polymers, are used as a fuel. In this
case, there’s no need to sort wastes; sometimes it’s required only to grind
wastes to large enough pieces to ensure their effective mixing with
carbon-containing fuel (mainly, coal), and to inject oxygen in combustion area.
To eliminate costs on grinding during combustion of worn tires, it’s proposed
to effect preliminary gasification of tires. For this purpose, Termex
Technologies, a Canadian company, has developed a tire gasification installation
which consists of 2 independent gasifiers each rated on 400-550 tires. To
initiate the process, small burners, which are turned into operation in 10 to 15
minutes before auto-combustion, are used. The process takes 6 to 8 hours. 2.8
tones of gaseous and liquid fuel with a calorific value of oil are obtained from
4.5 tones of tires. The installation is capable to process up to 500,000 tires
annually; production costs are recovered in 24-30 months.
For the time being, about 2,000
garbage disposal plants of various capacity are in operation worldwide. Many of
them don’t meet existing stiff ecological standards. Nevertheless, the most
advanced installations are highly mechanized and automated plants which
practically don’t contaminate the environment. In Germany, power plants using
municipal wastes as a fuel are planned for construction. One of these plants has
already been build and brought into operation near the town of Braunschveig.
Brief description of the plant is given below. The installation comprises the
following major components: a supply system, a hopper for waste, a boiler room,
a turbine house, a gas treatment system and a stack, and a system of slag
processing. Wastes are delivered to the plant in the form of pressed piles with
a volume of up to 3 cubic meters (cum) or in containers. The 20 cum hopper is a
storage where grinding and mixing of wastes takes place. The wastes are then
delivered from the hopper to the combustion line, where they are first dried at
the temperature of 80° C and then are burnt on the boiler grating at the
temperature of 1,200° C. Slag is directed to a water bath wherein salts are
dissolved. Then, rough impurities and metals are removed. After crushing and a
3-month storage, slag is used in road building. A 30 MW turbine is installed in
a turbine house and is fed with 71 tones of live steam entering it with a
temperature of 400° C and pressure 400 bars. To clean up flue gases, an
atomizing drier, bag filters, and an acidic and alkaline gas washer out of which
cleaned gases are rejected and withdrawn via a 120-meter stack to the atmosphere,
are provided. To reduce NOx emissions, a method of non-catalytic reduction with
injection of ammonia water in the first gas duct of the boiler is used. After
wet washing, a pulverized puddling coke is blown in and, together with salts,
dusts, heavy metals, dioxins and furans, is precipitated in bag filters.
In should be noted that a risk of
the environment contamination with super-toxins such as halogenated dioxins and
furans upon combustion of polymeric waste seems significantly overestimated and
in a major part relates to old garbage disposal plants (incinerators). At
temperatures of 1,200-1,400° C, typical for modern installations, these
substances are irreversibly decomposed; the undecomposed fraction is adsorbed in
adsorbing filters. Indeed, dioxin emission level at old garbage disposal plants
typically reach 300 mkg per a fuel tone; dioxin emissions at modern disposal
plants are only 0.6 mkg per a fuel tone, i.e. the emissions has been reduced
500-fold. To compare with, a tone of burning coal releases 1-10 mkg of dioxins,
and a tone of burning petrol releases 10-2,000 mkg of dioxins.
According to data obtained from
foreign resources, application of worn tires to generate heat and power is one
of the most rapidly-developing markets in the waste processing industry.
Combustion of tires separately or in mixture with coal (combined combustion)
provides the required heat capacity of boilers and cuts total fuel consumption.
Combined combustion is preferable, since ecological performance in this case is
better, than in the case when only tires are burnt. A rubber share in a fuel
shouldn’t exceed 20%. Fuel mixture should evenly be distributed over a grating
surface; intensive injection of air is to be provided. Tire pieces size
shouldn’t exceed 50 mm.
In Switzerland, France, the
Netherlands and North Europe, 50-80% of wastes are burnt to produce heat and
power. In Germany, 53 large plants annually burn 14.5 mln tones of wastes and
generate 2.1 trln Wh of electricity. The cost of burning a tone of wastes, on
average, is DM 316 for old plants and DM 120-230 for new plants. At the same
time, storage of a tone of garbage on polygons costs DM 200-400. For the time
being, in Germany only 10% of produced garbage are disposed to dumping grounds.
In Germany, a volume of wastes per each citizen is decreasing. The example of
Germany demonstrates that active position of the government and society helps to
effectively resolve the most complicated environment protection issues.
However, new challenges are
arising. Meteorologists are deeply concerned of a continuous average temperature
growth on the planet, which rises as many as 0.2K a decade. The phenomenon is
called “a greenhouse effect”, and it is solely anthropogenic in nature. This
phenomenon is a result of increased carbon dioxide concentration in the
atmosphere due to grown up emissions and undergoing deforestation process. To
reduce global warming rate, an aggregate amount of fuel people burn worldwide
has to be diminished. To hit the target, industry output has to be reduced. The
last International conference on this issue didn’t give any positive result,
since representatives of the USA and Japan didn’t support the proposals to cut
carbon dioxide emissions. World society has to endeavor to make a breakthrough
in this field.
Source: SciTecLibrary.ru -
Internet address: www.sciteclibrary.ru
Author: Ph.D. B. N. Anfimov
Publishing date: November 30, 2000