Reference Manual

8−6
tie is usually established with the local utility. This
also allows the mill to remain in operation if their
electrical production is curtailed or down
completely. Most mills try to use as little
purchased electricity as possible.
Waste Treatment
An important consideration for modern pulp and
paper mills involves the effective treatment of
water and air waste streams. Increased
environmental awareness has led to stringent
emission limits. This aspect of pulp and paper
mills could be one of the most controversial and
capital intensive areas in the future.
The primary concern for water is treatment of
effluent which is returned to the source (river or
lake). Water used in areas such as the pulp mill
and bleach plant picks up contaminants which
would make it harmful for fish and people. The
waste effluent is typically treated in sedimentation
clarifiers and/or aeration lagoons to remove
contaminants. Although some methods are highly
effective, future trends will be toward closed
systems with no effluent waste stream.
Air pollution from pulp and paper mills involves
both particulate and odor emissions. The major
sources of particulate emissions involve power
and recovery boilers. Fine particulate from various
sodium compounds are emitted from recovery
boilers and coarse particulate from burning wood
waste in the power boiler. Treatment for
particulate typically involves collection devices
such as scrubbers or electrostatic precipitators.
Although odor emissions in general are not
dangerous to the public, resentment due to the
smell requires pollution control application. The
various sulfur gases causing the odor are referred
to a TRS (Total Reduced Sulfur). Since odor
pollution is difficult to treat, in-process methods
resulting in less generation of odorous gases is
preferred. However, absorption of gases with wet
scrubbers is often used to achieve final
abatement.