Plastic Recycling
Whenever you throw a used plastic bottle into a recycling bin, you
feel a virtuous glow. With that simple action you have prevented the
bottle ending up on a landfill site, and allowed the valuable oil in
the material to be re-used.
Yet, however good your intentions, plastic recycling is less green
than you might imagine.
The recycled plastic most plants in the US and UK produce is not
clean enough to be turned into food or drink packaging, the largest
and most profitable market for plastics. Instead, it is converted
into industrial packaging and textiles, which earn the recycling
companies less money and make it difficult for them to compete with
firms in China and Vietnam where the recycling industry is
flourishing because of cheap labour and lax environmental
regulations. As a result, much of the plastic collected for recycling
in the US and UK is shipped to Asia.
What's more, the techniques used to remove contaminants from
plastic bottles before they can be recycled consume up to 2 litres of
water per 500 grams of recycled material. This means plants cannot be
built in areas where water is scarce. Waste from plants can also
pollute local rivers.
A new generation of plastics recycling plants promises to change
all that. The plants will use technologies that reduce or even
eliminate the need for water and produce plastics clean enough for
food packaging, at a lower cost than existing techniques. If
successful, such plants could significantly increase the number of
plastic bottles that are recycled in the US and Europe each year.
When a plastic bottle is sent to a conventional water-based
recycling plant it is shredded first. These shreds are placed in
float tanks that separate the polyethylene terephthalate (PET) used
to make the bottles, which sinks to the bottom, from the high-density
polyethylene used for the caps, which floats. The caps are removed to
be recycled separately. The PET shreds are then moved into another
tank of detergents, which eat away any glue and separate labels from
the material, before the plastic is melted down and readied for
reuse.
It is not hugely profitable: the plants typically earn around 1
cent per 500 grams of PET they recycle, thanks to their high water
and detergent bills, and to the low returns on selling the recycled
plastic for industrial packaging. Partly as a result of this low
profitability, plants are few and far between in the US - of the 530
million kilograms of PET collected for recycling in the US in 2005,
around half was shipped to Asia. The picture is even worse in the UK,
where nearly three-quarters of the 90 million kilograms collected for
recycling were shipped to countries like China.
In those plants that do operate in the US, the water left in the
float tanks at the end of the cleaning process, which is contaminated
with chemicals, glues and food residues, is treated with surfactants
to disperse the chemicals. Depending on state regulations, this water
either goes into the local sewerage system for further treatment, or
is simply released into rivers and streams. As a result, plants in
the US are regularly reprimanded for discharging waste water that
does not meet environmental standards, says Gary DeLaurentiis, who
ran a water-based recycling plant in Heath, Ohio, in the 1990s, which
was subsequently shut down. "All kinds of stuff gets into the
water, like pieces of labels and plastic, soap and surfactant,"
DeLaurentiis says. "We were paying a lot of fines for that."
"Seeing what water-based plants were discharging into the
environment made me start looking into different ways of recycling,"
says DeLaurentiis, who is now at ECO2 Plastics in Riverbank,
California. To clean up the industry and make it more profitable,
DeLaurentiis has developed a system for stripping bottles before they
are recycled that dispenses with water altogether so there is no
waste to pollute water supplies.
Shredded bottles are first immersed in the solvent ethyl lactate
to clean them, and then moved to a second chamber where they are
blasted with liquid carbon dioxide to remove any remaining solvent.
The solvent and CO2 are pumped into separate stills where
both are boiled off and the evaporated solvent and CO2
captured so they can be reused. You can then remove the distillate at
the bottom of the stills, mostly left-over solvent and contaminants
from the bottles, and dispose of it as solid waste. The cleaned
bottles can be melted down and processed into granules ready for
reuse in the conventional way.
The new process is cheaper than the water-based one, as the ethyl
lactate and CO2 are repeatedly reused. As there is no
liquid waste, plants do not need special waste permits, further
reducing the running costs.
"As there is no liquid waste, plants do not need special
waste permits, reducing costs"
Since ethyl lactate is derived from beets and corn, it has been
approved by the US Food and Drug Administration for use in cleaning
food-preparation equipment. ECO2's chief executive Rod Rougelot says
the solvent is safe for preparing plastic for recycling into food and
drink packaging. The company is waiting for endorsement from the FDA
before it can run its plant in Modesto, California, at full capacity,
when it will be able to recycle 27 million kilograms of PET annually.
By the end of the year it hopes to begin operating a second 27
million-kilogram plant in southern California. The company hopes to
earn up to 10 cents for every 500 grams of PET recycled.
The technology will be competing with more established cleaning
techniques such as the unPET process developed by United Resource
Recovery (URRC) of Spartanburg, South Carolina. This uses the caustic
agent sodium hydroxide to etch away a layer of contaminated PET from
the shreds, leaving behind only clean plastic. The mixture is heated
for four hours at 200 °C to speed up the process, after which any
remaining sodium hydroxide on the plastic is treated with a small
dose of phosphoric acid.
The first recycling plant to use the unPET process was built in
Switzerland in 2000, and there are now eight around the world. The
FDA has granted approval for plastics recycled in this way to be used
in food and drink packaging, so the plants can compete financially
with those in Asia.
The process is not yet suitable for areas where water is scarce,
such as California, as most unPET plants wash the plastic before
treating it, although they consume around half the water of
conventional plants. However, one unPET plant in Mullendorf, Austria,
repeatedly recycles a small amount of water, making it virtually
self-sufficient. Carlos Gutierrez, URRC's president, says the company
is exploring similar ways to recycle without water before building
plants in the western US.
Meanwhile in the UK, where water shortages are less of a concern,
most plastic bottles are shipped overseas for recycling because there
are no facilities to produce food-grade recycled PET. That is set to
change in December, when the first plant is scheduled to begin
operating in Dagenham, London. This will be based on URRC's process
and will recycle one-third of the 90 million kilograms of PET
collected in the UK each year.
The high price of oil is boosting demand for recycled plastics,
which is outstripping supply, so the new plants cannot be built
quickly enough, says Patty Moore of Moore Recycling Associates in
Sonoma, California. "Right now we have economics that are pretty
favourable for expanding recycling. The environment has changed from
barely scraping by to people saying, 'hey, we can make some money at
this'."
From issue 2603 of New Scientist magazine, 09 May 2007, page 28-29
One bin better than two
As more recycling plants are built in the US and Europe and demand
for plastics increases, the supply of bottles from local collections
is struggling to keep up.
Only 23 per cent of all polyethylene terephthalate bottles used in
the US were collected for recycling in 2005. If this persists, it
could hamper efforts to increase recycling and reduce the amount
shipped to Asia.
Most municipalities ask consumers to separate recyclables into
several small bins for paper, glass and plastics. But if collection
schemes are too elaborate, people don't bother. At a meeting of the
Oregon Department of Environmental Quality in Portland on 30 April,
officials presented research that compared participation in
collection programmes in areas of the state that used several
separate bins with those using a single, large roll-cart, or wheelie
bin. They found that retrieving waste weekly from a single roll-cart
almost doubled the amount of plastic collected (see Graph).
In the UK, a similar report issued last month by the Local
Government Association found that overall recycling rates rose from
23 to 30 per cent when recyclables were picked up one week and
regular trash the next. "This is the kind of information we need
to get more plastics recycled," says Patty Moore of Moore
Recycling Associates in Sonoma, California. "No one's going to
build a plant if they're not going to get the feedstock."
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