Irina Calante, currently an Environmental Engineering graduate
student at UNH, is working with Dr. Kevin Gardner on in-situ remediation
of contaminated marine and freshwater sediments. Irina's specific
aspect of the research is to optimize the dechlorination of polychlorinated
biphenyls (PCBs) in sediment with different reducers by determining
rate limiting factors through sediment characterization, reducer
concentration, and rate of reaction. The reducer of focus is zero
valent palladized magnesium (Mg/Pd) where the magnesium is the reactant
and the palladium acts as a catalyst only. The main objective is
to create a remediation technology for PCB contaminated sediments
that actually degrades the PCBs. This technology would be able to
be applied in-situ as well as ex-situ. It would provide an alternative
to the most common remediation methods used today, dredging and
caping, which isolate the contaminant but do not reduce its concentration.
Bench scale experiments so far have shown dechlorination of PCBs
in sediments with Mg/Pd (Figure 1). The dechlorination efficiency
is dependent on the initial PCB concentration in the sediment, the
organic content, the sediment composition as well as the amount
of Mg/Pd. Desorption experiments have also been conducted to determine
whether PCB desorption from the sediment is a limiting factor for
dechlorination (Figure 2). Based on the dechlorination efficiency
achieved so far, desorption does not seem to be a rate limiting
step. However, it might be rate limiting for the most inaccessible
PCBs confined in the sediment. Solvent experiments were conducted
to see if solvents would increase the availability of the PCBs from
the sediment. The addition of two terpene based solvents did not
improve overall dechlorination wit Mg/Pd when compared to the addition
of water (Figure 3).
|Figure 1. Cumulative percent PCB desorption
from two sediments, Housatonic River and New Bedford Harbor,
over 50 days.
|Figure 2. Percent PCB dechlorination in
New Bedford Harbor sediment with 0.2g Mg/Pd after 4 days.
|Figure 3. Average PCB dechlorination in
New Bedford Harbor sediment with 1g Mg/Pd, 10mL distilled water
and 7.5mL of solvent after 48 hours.
Dr. Kevin Gardner
Center for Contaminated Sediments Research
336 Environmental Technology Building
University of New Hampshire
Durham, NH 03824