Environmental Engineering Reference
In-Depth Information
of the superhydrophobic powder are that the material is environmentally compatible and
is low cost. To date, it is unknown how such methods would work on emulsiied oil-water
systems; however, this technology development will be interesting to follow to see if it has
applications for bilge water treatment.
7.4.2 Organoclays and Modified Polymers
Surface modiication of clay particles has also been investigated for oil-in-water removal.
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In general, organoclay technology has not yet involved nanoscale engineering; however,
the use of organoclay is worth noting because of the low cost of the media relative to other
technologies. Organoclays have been successfully used as a coalescence and iltration
media for emulsiied oil. Typically, bentonite or other clays are used and made oleophilic
by treatment with quaternary amines that bind to the surface by a charge-charge interac-
tion. Organoclays remove ive to seven times the amount of emulsiied oil compared with
activated carbon.
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Therefore, these materials are often used as prepolish media with an
estimated cost savings of about 55% for the media compared with carbon. Polymer sup-
ports have been used as an alternative to clay-based systems. For instance, isobutyl meth-
acrylate polymers (ELVACITE
®
2045) have been modiied with an oily coating to create an
absorbent ilter media available commercially as MYCELX
®
. The MYCELX system has been
pilot tested to treat bilge water (220 gal/min) at a shipyard-based facility.
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According to
the study, bilge water could be treated for $US0.02/gal at the dock using a completed sys-
tem. Neither modiied clays or modiied polymers can be regenerated and thus may only
practically be used at onshore treatment facilities where media can be stored and replaced.
It will be interesting to see if nanotechnology approaches can be applied to organoclay
materials to improve performance.
7.4.3 Nanoengineered Animated Organosilica
Organosilica materials that rapidly swell have been created using the sol-gel method
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where
alkoxysilane precursors are polymerized to form Si-O-Si linkages. The name is derived from
the fact that a system starts as a solution of monomers that upon polymerization yields a gel
state when suficient cross-linking increases the viscosity. Solvents can be removed after gela-
tion to yield hard materials and ceramics with various chemical compositions and nanoscale
architectures.
59,60
The sol-gel method is versatile in that properties of the inal material (e.g.,
surface composition, pore size, morphology, hydrophobicity) can be carefully controlled by
the choice of precursor, kinetics of polymerization, and postgelation processing steps.
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7.4.3.1 Physical Characteristics
Nanotechnological approaches have been used to create organosilica absorbents that have
high capacity for the removal of organics from water.
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The materials are created from
molecular scale self-assembly to generate nanoscale particles that spontaneously assem-
ble into an interconnected, yet highly lexible matrix (Figure 7.8). On the macroscale, the
organosilica looks like glass but swells up to eight times its mass when absorbing organic
liquids, as the nanoengineered matrix expands to a relaxed state.
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Interestingly, the swell-
ing due to incursion of organic liquids is both extremely rapid and forceful. Swelling can
produce >200 N/g of force
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derived from tension within the dry and collapsed matrix,
meaning the absorption of oil can cause the sorbent to lift 20,000× its own weight. The
surface area and pore volume are relatively large: 500-1000 m
2
/g and 0.6-2.5 mL/g,
