Introduction - Principles of Chemical Separations with Environmental Applications - page 5

Pollution of soils also occurs through a variety of sources. Municipal and industrial
waste has been buried in landfills, which sometimes leak, even if lined with durable
impermeable materials. Periodic news accounts of hazardous chemicals migrating through
soil to threaten water supplies and homes are reminders of this issue. Chemical discharge
directly onto surface soil from periodic equipment cleaning, accidental discharges (spills),
abandoned process facilities or disposal sites is another environmental challenge. Sub-
surface contamination can also occur as a result of leaking underground storage tanks.
In addition to air, water, and soil pollution, large quantities of solid and liquid wastes
generated by both industry and domestic use must be remediated, recycled, or contained.
Industrial wastes include overburden and tailings from mining, milling, and refining, as
well as residues from coal-fired steam plants and the wastes from many manufacturing pro-
cesses. The nuclear and medical industries generate radioactive solid wastes that must be
carefully handled and isolated. Effective ways of fractionating long-lived radioactive iso-
topes from short-lived ones are needed because the long-lived ones require more expensive
handling and storage. The environmental problems of residential wastes are increasing as
the population grows. It is important to segregate and recycle useful materials from these
wastes. In many places, there are no effective options for dealing with toxic liquid wastes.
Landfill and surface impoundment are being phased out. There is a strong incentive toward
source reduction and recycling, which creates a need for separations technology [1].
All of the above separation needs are oriented primarily toward removal and isolation
of hazardous material from effluent or waste streams. Pollutants are frequently present in
only trace quantities, such that highly resolving separation systems will be required for de-
tection and removal. The problem of removing pollutants from extremely dilute solutions
is becoming more important as allowable release levels for pollutants are lowered. For ex-
ample, proposed standards for the release of arsenic prescribe levels at or below the current
limit of detection. Another example is pollution of water with trace quantities of dioxin. In
research being carried out at Dow Chemical USA, concentrations of adsorbed dioxin at the
part-per-quadrillion (10 15 ) level have been successfully removed from aqueous effluents.
That technology has now been scaled up, such that dioxin removals to less than ten parts
per quadrillion are being achieved on a continuous basis on the 20 million gallon per day
wastewater effluent stream from Dow's Midland, Michigan, manufacturing facility.

1.5 Environmental separations

Based upon sources of pollution and the nature of polluted sites (air, land, or water),
environmental separations can be categorized as follows.
1 Clean up of existing pollution problems
Examples:
surface water contamination (organics, metals, etc.)
groundwater contamination (organics, metals, etc.)
airborne pollutants (SO x ,NO x , CO, etc.)