Environmental Engineering Reference
In-Depth Information
practice currently used for KMnO
4
and TCE remediation. The formation of MnO
2
precipitates which, is also a significant problem for traditional KMnO
4
remedia-
tion, still remains an important consideration and potential challenge to overcome
for CRBP remediation.
Literature reports one of the limiting factors for chemical oxidation methods
is the formation of precipitates that will “clog” the soil particles and reduce the
effectiveness of transporting chemox liquid to the subsurface [25-27]. In previous
liquid KMnO
4
studies, the system formed solid manganese oxide (MnO
2
) precipi-
tates which act as a barrier in the destruction of TCE. Preliminary data suggest the
erosion based pellets produced MnO
2
precipitates within 24 h which supports the
need to design CRBP which minimizes MnO
2
production. The precipitate produc-
tion, however, subsided for the diffusion based prototypes using the hydrophobic
polymers.
Literature also suggests that permanganate can react with soil constituents
such as natural organic matter; this reaction with natural organic matter must
be accounted in the determination of the optimal concentration of KMnO
4
to
deliver from the pellets [25]. These side reactions are characteristics of all chemox
treatments (i.e. ozone, Fenton's Reagent, KMnO
4
) because of their ability to non-
discriminately react with other chemicals. This characteristic is why chemical
oxidants are applied in higher than stoichometrically required ratios to account for
oxidant loss. This aspect of chemox is inherent to the use of highly reactive chemox
compounds. Therefore it may be a characteristic that will not be easily altered but
should not decrease the interest in using chemox methods. To overcome this dif-
ficulty, current chemox methods increase the molar ratio of oxidant injected into
the system based on the premise that side reactions will occur decreasing oxidant
efficiency. For permanganate reactions with TCE, 2-mole of KMnO
4
will stoichio-
metrically react with 1-mole of TCE. The system for KMnO
4
delivery from the
pellets can be adjusted by providing a higher dose of KMnO
4
in the treatment sys-
tem than the 2-mole KMnO
4
: 1 mole TCE thus making this method comparable to
liquid and gaseous oxidant reactions occurring in the field. Literature reports the
observed stoichiometric ratio for permanganate to TCE as 3.5-5 moles KMnO
4
for
every mole of TCE using waxy pellets in aqueous systems [24, 28, 29]. Preliminary
studies show the polymers are moderately soluble in TCE. This finding was also
supported by research conducted with the chlorine-based polymers used in Ross
et al. [18]. This observation may facilitate the release of the potassium perman-
ganate from the pellets in the presence of TCE and additionally some TCE may
diffuse into the pellets and become entrapped within the polymer thus aiding with
remediation.
2.4 Future Considerations and Conclusion
Biodegradable polymers offer an attractive alternative for improving remediation
methods for environmental engineering applications. Exploring the ability to use
biodegradable polymers featuring controlled release capabilities for environmental
