Environmental Engineering Reference
In-Depth Information
The diffusion based prototypes containing Polymer A proved to be the most
effective KMnO
4
delivery without the formation of MnO
2
precipitates. The ero-
sion based prototypes with Polymer B formed manganese oxide precipitates. The
diffusion based and the combined prototypes were determined to be more feasible
for long-term release of the oxidant subsurface. The prototypes with a higher ratio
of Polymer B produced MnO
2
precipitate which decreased in formation as the ratio
of Polymer A polymer increased in the pellet design. Because manganese oxide is a
precipitate known to inhibit the ability to use KMnO
4
for trichloroethylene remedi-
ation, the PAB-100 prototype was evaluated for the media replacement, continuous
release, and TCE remediation studies.
2.3.3.1 Replacement Media Study
In the replacement media study, PAB-100 prototypes containing 2 and 20% KMnO
4
by mass to polymer ratio were encapsulated in the polymer shell. In batch reactor
bottles, 50 ml of DI water and 0.5 g of prototype pellets were sealed and stored
for 3-4 days at 28
◦
C and in the dark. After 3-4 days, the KMnO
4
concentration
was measured using a Spectronic Spectrometer at 525 nm wavelength. Following
the KMnO
4
concentration measurement, the pellets and bottles were rinsed with
DI water three times and 50 ml of fresh DI water was added to the bottles with
the same pellets. This process was then repeated by storing the reaction bottles
for another 3-4 days and a KMnO
4
measurement was performed. This replace-
ment media study was designed to measure the steady-state release rate of KMnO
4
prototypes.
The prototypes demonstrated an initial rapid release of the oxidant followed by
a slower, steady state release (Fig. 2.5a and b). The 2% prototype exhausted the
encapsulated KMnO
4
diffusing from the shell within 44 days. The 20% KMnO
4
structures however had not exhausted the oxidant within the 44 day period of the
experiment. It is hypothesized this prototype would be able to continue to release
KMnO
4
release for a significantly longer period due to the higher concentration of
KMnO4 encapsulated in the polymer prototype.
2.3.3.2 Continuous Release Study
In the continuous release studies, PAB-100 prototypes containing 2 and 20%
KMnO
4
by mass to polymer ratio were encapsulated in the polymer shell. A mass of
0.5 g of pellets were added to 50 ml of DI water in reaction bottles. Measurements
for KMnO
4
were conducted every 3-4 days using a Spectronic Spectrometer at
525 nm wavelength. Following the measurements, the prototypes and the liquid
sample were returned the bottles, capped, and stored for another 3-4 days at 28
◦
C
in the dark before the next measurement. In the continuous batch study, KMnO
4
release was observed to extend over a 46-48 day period where 2 and 20% KMnO
4
by mass in polymer prototypes were measured for KMnO
4
concentration in water
(Fig. 2.6a and b).
