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Zero-effluent
– a new approach for pulp mills
Virtually all pulp mills in the
world discharge liquid effluent, or waste water, into rivers
or oceans following treatment to remove contaminants. But
the site Canadian company Millar Western had chosen for its
new bleached chemi-thermo-mechanical pulp (BCTMP) mill near
Meadow Lake, Saskatchewan, posed a unique challenge. Without
a nearby water body suitable for receiving effluent, the company
set out to build the world's first successful zero-liquid-effluent-discharge
market pulp mill. In operation since 1992, the mill remains
one of only two such mills in existence today and has worked
superbly from both environmental and productivity standpoints.
Because it cleans and reuses all its waste water, the mill
requires significantly less fresh-water intake than other
pulp mills. To bleach its pulp the company uses hydrogen peroxide,
which, unlike the chlorine-based compounds employed by most
pulp mills, breaks down harmlessly and does not release dioxins,
furans or other chlorinated organics to the environment. The
mill also practices chemical recovery, reusing byproducts
such as caustic in the pulping process.
Another environmental feature of
this mill is the kind of pulp it makes. BCTMP mills can yield
up to twice as much pulp per tree as conventional pulp facilities,
resulting in fewer trees being harvested for every tonne of
pulp produced. The Meadow Lake mill uses only aspen trees
– an abundant, fast-growing species that is easily and
naturally regenerated. Until Millar Western began expanding
the market for aspen pulp, aspen had little commercial application
in the forest products industry. Today, aspen BCTMP is highly
valued by papermakers in Europe, Asia and North America for
use in printing and writing papers, specialty papers and paperboard.
Pioneering developments like these have helped position Millar
Western as the technical and environmental leader in the BCTMP
industry.
Electricity generation
When we wash clothes or shower,
the water is not 'consumed' and returns quickly to our waterways.
When we water our lawns, the water is 'consumed' through a
process of evaporation or transpiration. It takes days or
weeks before this water vapour condenses and returns to earth
as precipitation, most of the time far away from where the
water was consumed.
In Saskatchewan, thermal generation
of electricity is one of the largest consumers of water. The
water is used for cooling purposes. Large amounts are continuously
drawn into power stations and the same amount of water is
discharged after it has been used to cool the steam condensers
in the power station. However the temperature of the water
that leaves the power station has been increased and once
the water is released it evaporates at a much higher rate
than would have been the case before its temperature was increased.
This higher rate of evaporation from the warmer water represents
water 'consumption' and even though the evaporation will eventually
return to earth in the form of precipitation, it is considered
to be 'consumed', from the area where it was taken.
Water in Saskatchewan is also used
to produce electricity at hydro generating stations where
the water upstream of a dam flows through a powerhouse and
drives a turbine-generator that produces electricity. Although
this water is used to generate electricity, it is not 'consumed'
since it remains unaltered and continues to flow downstream
in the river where it originated. However, since most of Saskatchewan's
electricity is generated at thermal power stations, the electricity
generation sector is one of the largest consumers of water
in the province. |
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