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Material reprocessing
PETE: Polyethylene terephthalate
Recycle code 1
HDPE: High density polyethylene
Recycle code 2
UPVC: Unplasticised polyvinyl
chloride Recycle code 3
Mechanised separation &
After, material separation at a
Material Recovery Facility mixed
plastics PETE, HDPE & UPVC are
bulk hauled in a compacter to a
plastics reprocessing factory
Separation Infra – red Sort 1
A fully computerised machine
using Infra-red light identifies the
different plastics by their chemical
structure and separates into
individual plastic type
A whole bottle wash removes dirt,
glue and labels.
Chop the separated plastics into
flakes. Each plastic type has it’s
own special grinder.
Washing 2
PETE and UPVC plastic flake is
washed in heated water treated
with detergents and additives.
HDPE is washed in cold water.
The separated flake is dried,
weighed and bagged, before it is
fed to the extruder.
The extruder melts the plastic
flake. The extruder has a die and
cutter at the end of it. The plastic
emerges as strands and is cut into
Infra–red Sort 2
Identifies and separates clear and
coloured HDPE and PETE. UPVC is
identified and separated by X Ray
PETE flake is separated from PP
cap and ring seal pieces in a
flotation tank. The two plastics
have different densities. The PETE
sinks to the bottom while the PP
floats to the surface and is
skimmed off.
The pellets are then bagged ready
to be sold to manufacturers as
secondary raw material for the
manufacture of new plastic
After, material separation at the
Material Recovery Facility glass is
bulked hauled to a secondary
sorting plant where it is dumped
into a hopper ready for colour
separation and crushing into
cullet (small pieces).
Metal contamination in the
form of caps and lids is removed
by magnets and eddy - current
separators Further contamination
is removed by computerised
optical sorting machines and
separation into the 3 main colour
types for glass containers: Green,
Clear & Brown
The colour of glass is
determined in the original
manufacture process by the
addition of various colouring
agents, such as, chrome (green)
and coal (brown). Once the
colour is added it cannot be
removed. Therefore brown bottles
can only make other brown
Recycled glass cullet is sold to
packaging manufacturers such as
ACI for the production of new
glass bottles and jars. The $ value
of recycled glass cullet is largely
dependent on how clean it is ie
free of other material
contamination and the
consistency of colour segregation.
Why Recycle Glass
Environmental benefits:
— Reduces manufacturing
related air pollution by 20% and
water pollution by 50%
— Saves energy because
recycled glass can be processed
at a lower temperature than new
glass made from raw materials
— Reduces Greenhouse gas
emissions associated with the
burning of fossil fuels in
transportation of raw materials to
glass manufacturing plants.
Sources of recycled glass are
usually located closer to glass
packaging plants.
— Save resources. 14 billion
bottles and jars are thrown away
in the USA every week
GLASS Raw materials: Sand, Soda Ash and Limestone
Not all glass is the same
Glass is 100% recyclable but
because the formulation of glass
varies according to application,
only glass bottles and jars can be
recycled into glass bottles and
The glass used for light bulbs,
cookware and windows is made
with the addition of ceramics.
Heat resistant glass also melts
at a different temperature than
the glass used to make bottles
and jars.
Is it Recycled
The recycled glass content of
glass packaging produced in
Australia is on average 44% and
sometimes more than 60%.
Material reprocessing
ALUMINIUM CAN Raw materials: Bauxite
After material separation the
aluminium can bales are
transported to an aluminium
smelting plant.
On arrival the bales are
unloaded and tested for quality
and moisture content.
The bales are then broken up
and the cans shredded into small
De- lacquering
Paint and residual moisture is
burnt off the shredded cans in a
De-lacquering oven
The hot shredded aluminium
is then screened to remove dirt
and contaminants before being
fed into a furnace.
Heated to 650o Centigrade the
cans melt and blend with the
molten metal already in the
The molten aluminium is
checked for correct chemical
composition and then poured
into moulds. The resulting ingots
are allowed to cool and harden.
New Aluminium Can
To make aluminium sheet
suitable for can manufacture the
ingots are “Scalped”. Scalping is
where the top and bottom layers
of the ingot are milled to a
smooth surface.
The ingot is then passed
through a large rolling mill many
times and heated, and then rolled
again until it reaches the
necessary hardness and thickness
for can manufacture
A roll of aluminium sheet
suitable for making cans may
measure 2-3 kilometres and be
made from over 1.2 million
recycled cans
After material separation the steel
can bales are transported to steel
A bale of used steel cans
weighs 1 tonne and contains
around 14,000 cans
At the steel mill the bales are
broken up before de-tinning
The tin plate that protects the
steel can from corrosion and the
contents from spoilage is
The de-tinned steel can
material is shredded and used in
the making of new steel
Around half of the 700 million
tonnes of crude steel produced
globally each year will be
recycled as scrap.
Every tonne of scrap steel used in
steel making saves 3 tonnes of
natural resources
Raw materials
— Iron ore
— Coal converted to coke
— Limestone
— Steel scrap
At a paper reprocessing plant the
paper is sorted by hand to
remove obvious contamination
and separated into various grades
of paper such as newsprint, office
paper, cardboard etc. Newsprint
is the lowest grade of paper.
The better the quality of paper
collected the higher the quality of
recycled paper produced. Unsorted
paper can be used for packaging.
Much of the packaging found on
supermarket shelves is recycled.
Compacted into bales the
paper is then transported by
truck to a paper mill.
At the mill, the waste paper is
mixed with water in a machine
similar to a washing machine.
The resulting pulp is a mixture of
water and cellulose fibre, the
long thick walled cells of plants
that gives stems and trunks
rigidity and strength.
During pulping contaminants
such as plastic covers and metal
in the form of paperclips and
staples are removed.
The pulp is then filtered
through wire mesh screens to
remove the water.
Passed through presses and a
dryer to remove any remaining
water the paper is then spun into
huge reels ready to be made into
new paper product.
Steel making
— Blast furnace - Iron making
— Electric Arc furnace– Steel
— Basic Oxygen furnace – Steel
Material reprocessing
PAPER continued
Paper that has been printed such
as newspapers and magazines
must have the ink removed
before it can be recycled into new
paper product.
To do this the pulp is de-inked
by washing it in a mixture of
detergent and aerated water to
form a bubbly froth.
The resulting inky froth is
skimmed off leaving an ink free
pulp ready to be made into paper
How many times can paper
be recycled?
Waste paper can be recycled
about 5-10 times before the
cellulose fibres become so short
and weak they can no longer
mesh together to form a sheet of
— Green Waste - Plant debris such as leaves and grass clippings
— Food Waste – Surplus food and fruit and vegetable peelings
COMPOSTING Who’s Eating Who
A complex food web is at work
in your home compost heap.
The conversion of green and
food waste into nutrient rich
compost is the sum of the
actions of invertebrates such as
millipedes, snails, slugs and
earthworms along with bacteria
and fungi as they live, eat,
excrete and die. As each
decomposer dies or excretes,
more food is added to the web
for other decomposers
The invertebrates shred the
organic material creating a
greater surface area for bacteria
and fungi to do the bulk of the
decomposition work and heat
Many kinds of worms
including earthworms and
nematodes eat the decaying
vegetation and microbes and
excrete organic compounds that
enrich the compost. The
tunnelling of worms also aerates
the compost
Bacteria are the smallest living
organisms making up to 90% of
the billions of micro-organisms
found in a gram of compost.
Bacteria are responsible for >
— America has a population of
approximately 288 million
people. Every day Americans buy
62 million newspapers and throw
away 44 million, the equivalent
of dumping 500,000 trees to land
fill each day.
— In Australia about 26% of
newsprint is recycled paper.
— Australia imports more than
50% of the printing and writing
paper used here.
— Laser printed paper cannot be
recycled back into printer paper
because the ink is melted onto
the paper and is too difficult and
costly to remove.
Material reprocessing
COMPOSTING Who’s Eating Who continued
most of the decomposition and
heat generation in a compost
Bacteria use a broad range of
enzymes to chemically break
down organic material into
Bacteria and fungi are also
eaten in turn by organisms such
as mites.
Various species of bacteria are
present at each of the various
heat stages in the
decomposition. There are
3 stages of heat generation
in decomposition:
A moderate temperature
phase 0-40oC lasting a couple of
A high temperature phase
40-60>oC which can last
anything from a few days to a
couple of months
A cooling and maturation
phase which can last serval
Decomposition, in the
moderate heat phase, is carried
out by bacteria commonly found
in topsoil, as the temperature
increases above 40oC the
dominant species is Bacillus.
At high temperature the genus
Thermus is present. These
micro-organisms can withstand
extremely high temperatures.
Compost Chemistry: Getting the
Recipe Right
Carbon and nitrogen are the
most important elements in the
decomposition process. Carbon
is both the energy source and
the basic building material of
microbial cells and of course all
forms of life on Earth. Nitrogen
is the crucial component for cell
growth and function.
Carbon–to–nitrogen ratio:
To achieve efficient decomposition
the carbon–to–nitrogen ration
should be 30:1 or 30 parts
carbon, by weight, for each one
part that is nitrogen.
Why 30:1?
At lower ratios, nitrogen will be
supplied in excess and will be
lost as ammonia gas, causing
odour. Higher ratios mean that
there is not enough nitrogen for
microbial population growth, so
the compost will remain
relatively cool and degradation
will be slow.
Green & Brown
Materials that are green and
moist are high in nitrogen, and
those that are brown and dry
are high in carbon. High nitrogen
materials include grass
clippings, plant cuttings, and
fruit and vegetable scraps.
Brown or woody materials such
as autumn leaves, woodchips,
sawdust, and shredded paper
are high in carbon.
Most of the nitrogen in
compostable material is readily
available. Some of the carbon,
however, may be bound in
compounds that are highly
Material reprocessing
COMPOSTING Who’s Eating Who continued
resistant to biological
degradation. Newspaper, for
example, is slower than other
types of paper to break down
because it is made up of
cellulose fibres covered in lignin,
a highly resistant compound
found in wood.
Oxygen is another essential
element for composting. As
micro-organisms oxidise carbon
for energy, oxygen is used up and
carbon dioxide is produced.
Without enough oxygen, the
process will become anaerobic
and smell.
How much oxygen do aerobic
microbes need?
Aerobic microbes can survive on
oxygen concentrations as low as
5%. Though concentrations of
more than 10% are best for
maintaining aerobic composting.
This can be easily achieved by
turning and mixing compost
A pH between 5.5 and 8.5 is
ideal for compost microorganisms. As bacteria and fungi
digest organic matter, they
release organic acids. In the early
stages of composting, these acids
often accumulate. The resulting
drop in pH encourages the
growth of fungi and the
breakdown of lignin and
cellulose. Usually the organic
acids break down further during
the composting process. If the
system becomes anaerobic,
however, acid accumulation can
lower the pH to 4.5, severely
limiting microbial activity. In
such cases, aeration through
turning and mixing is usually
enough to return the compost pH
to acceptable levels.
Compost Physics:
Size Does Matter
The rate at which composting
occurs depends on physical as
well as chemical factors.
Temperature is a key factor as
well as the physical
characteristics of the compost
ingredients such as particle size
and moisture content.
Particle Size
Microbial activity generally occurs
on the surface of the organic
particles. Decreasing particle size,
through its effect of increasing
surface area, will encourage
microbial activity and increase the
rate of decomposition. When
particles are too small and
compact, air circulation through
the pile is inhibited. This
decreases the amount of oxygen
available to micro -organisms and
decreases their activity. Particle
size also affects the availability of
carbon and nitrogen. For example,
large wood chips are a good
bulking agent that ensure aeration
through a compost pile, but they
provide less available carbon per
mass than they would in the form
of wood shavings or saw dust
System Size
The size and shape of the
compost system (eg wind row or
compost bin) affects the type and
rate of aeration and the ability of
the compost to retain or dissipate
the heat generated.
Temperature: Just Hot Enough
Temperature is a key factor in
successful composting. The heat
generated is a by-product of the
breakdown of organic material
and is dependent on moisture,
aeration, C/N ratio and ambient
temperature. The temperature at
any point during composting
depends on how much heat is
being produced by micro
–organisms, balanced by how
much is being lost through
conduction, convection, and
Sufficient heat needs to be
generated to destroy plant
diseases, fly larvae and weed
seeds but not so much that it
affects beneficial composting
micro-organisms that cannot
survive temperatures above 6065C. Turning to aerate the
compost reduces temperature.
Aeration: A Breath of Fresh Air
Oxygen is essential for the
metabolism and respiration of
aerobic micro -organisms, and
for the oxidisation of the various
organic molecules present in the
waste material.
At the beginning of biological
decomposition oxygen levels are
similar to that of air. As microbial
activity increases oxygen levels
drop and carbon dioxide levels
increase. If oxygen levels fall
below 5%, anaerobic conditions
will develop resulting in odour.
Regular mixing and turning
will aerate the compost pile and
maintain aerobic conditions.
Moisture: As Damp as a Wrung
out Sponge
Moisture content of 50 – 60% is
considered ideal for composting.
Microbe induced decomposition
occurs most rapidly in the thin
liquid films found on the
surfaces of organic particles.
Moisture content of less than
30% reduces bacterial activity.
Moisture content greater than
65% results in slow
decomposition, odour and
nutrient leaching
Source: Cornell University USACornell Composting – Science
& Engineering web
Authors: Richards, Trautmann
et al