Page 503 - Air Pollution Control Engineering

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Emerging Pollution Control Technologies 475

dependent on the pressure ratio (permeate-side pressure to inlet pressure) and the mem-
brane material. To achieve high removal efficiency, the membrane material should
demonstrate high permeability and good selectivity for the solvents to be recovered.
Additionally, the membrane should be durable and stable enough to withstand normal
wear during operation.
One can optimize the membrane selectivity by choosing a balance between the
capital cost of membrane area and the energy cost for pumping. Additionally, the opti-
mum membrane selectivity is determined by choosing the lowest selectivity that will
produce the desired permeate concentration. When the solvent flux is decreased
(more membrane area per flow of solvent), the membrane selectivity is increased. By
comparison, the energy requirement for a low-selectivity membrane is greater
because more energy is required to pump a higher volume of gas to meet the perme-
ate requirements (at fixed permeate pressure). Therefore, the selection of a membrane
must be a balance between capital cost for the membrane (the greater the membrane
area the higher the capital cost) and the operational cost (the greater the pumping rate,
the higher the energy cost) (30).
Weller and Steiner (31) presented the fundamental mass and energy balance equa-
tions that govern the design and performance of a single-stage gas permeation system.
Additionally, Pan and Habgood (32) performed analysis on a crossflow pattern that
applies to the spiral-wound membrane. The assumption for these analyses may be sim-
plified as follows: the permeability of both components constant, negligible pressure
drop across flow paths, and negligible mass transfer resistances except for permeation
through the membrane. In test studies, for most cases, the error introduced by assuming
constant permeability was not found to be excessive (26).
A small membrane test unit can be utilized to generate representative samples of
concentrated feed and filtrate that demonstrate pollutant separations. Such small mem-
brane testing units are commercially available (33, 34).
The feasibility of using full-scale membrane separation process for control of has
been studied and reported by Moretti and Mukhopadhyay (35).
Section 10 compares the membrane process with other emerging and conventional
processes for VOC control. The innovative membrane process, at present, is only
designed for removal of VOC from air emission streams. It is unknown whether or not
the membrane process can remove any particulate matter (PM) or heavy metals from air
emission streams, although it is a filtration process in principle.
8. ULTRAVIOLET PHOTOLYSIS

8.1. Process Description
Since 1988, ultraviolet (UV) light technology has been used for the destruction of
toxic organics in aqueous solutions. UV light has also been used as a primary treatment
process, but in some cases, it has been used in conjunction with ozone and hydrogen
peroxide, which serve as oxidants (36).
Researchers have recently shown that UV photolysis of organics can be accom-
plished by utilizing a broad spectrum of high-intensity UV light. These experiments
include treating water, air, and soil. Promoters of direct UV photolysis have claimed that
it can be used to disintegrate toxic organic toxics into nontoxic byproducts. Ultraviolet