Underground Construction - August 2022 - 33

EDITION 76 | AUG 2022 | NASSCO.ORG
The GAC method lends itself to using more than
activated carbon alone. Many suppliers of this
medium also offer media that contain a combination
of ingredients. As an example, one supplier offers a
medium that is a combination of activated carbon
and potassium permanganate. This combination
offers more efficient removal of some types of
contaminates.
The design of the unit is more complicated than just
designing the cannister size. To maximize carbon
life, the effluent passing through the unit should be
cooled and dehumidified in the case of air, and
should be cooled in the case of a liquid effluent. An
engineer familiar with the CIPP process and this
treatment method can design an efficient unit. Figure
2 is a simplistic view of the GAC process.
The cost of using the GAC process varies with the
amount of effluent to be treated, the concentration
of the contaminant in the effluent, and the media
used in the unit. Assuming a set of variables, one
calculation estimates a cost of slightly less than
$14.00 per pound of styrene removed from the
effluent stream.
While chemical process methods provide several
alternatives for removing styrene from the CIPP
process, other alternatives exist. UV light cured
processing of CIPP liners has been shown to
reduce styrene emissions into the atmosphere and
into the process water after the line has been
returned to service. The method used by UV light
cured processing is the introduction of a specific
barrier between the resin-containing layer and
either water or air that may meet that liner. Styrenefree
resins have been available for several years and
have been proven to be a viable alternative to
styrenated resins.
A new option is now available for heat cured CIPP
liners. This option utilizes similar technology to
barrier coatings used by UV cured liners. One of the
largest manufacturers of dry tubes used in heat
cured CIPP has introduced a polyester felt liner
containing a polyamide layer in the barrier coating.
Unlike UV light cured liners, these tubes may be
inverted in like manner to currently available heat
cured bags. Historically, barrier coatings tend to be
polyurethane, polyethylene, or polyolefin, all of
which are permeable to styrene. The polyamide
component, like that used in UV coating's " foils " , is
impermeable to styrene. This minimizes styrene
that may pass through the barrier into the air or
water in CIPP heat cures. The degree to which
styrene emissions are reduced is currently being
determined by contractors using this new tube.
Figure 2. GAC Unit for gaseous effluent
With these existing and newer technologies, styrene
emissions into the atmosphere from the CIPP
process may be of significantly lower concern.
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Underground Construction - August 2022

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