ELECTROKINETIC%20REMEDIATION%20OF%20CONTAMINATED%20SOILS%20AND%20POLLUTION%20MONITORING%20INVOLVING%20GIS%20TECHNOLOGIES

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ELECTROKINETIC REMEDIATION OF CONTAMINATED SOILS
AND POLLUTION MONITORING INVOLVING GIS
TECHNOLOGIES Ovidiu Anicai1, Roxana Dumitrache2,
Mihai Dutu2, Constantin Ana2 1Institute for
Computers ITC SA, Calea Floreasca 167, Sector
1, Bucharest, oanicai_at_itcnet.ro 2 PSV COMPANY SA,
Div.of Ecological Technologies Development,
Calea Grivitei 8-10, 010772, Bucharest
Motivation
Among in-situ restoration technologies based
on physical-chemical phenomena, the
electrokinetic remediation attracted an increased
interest of scientists and final users. It can be
applied alone or associated with other treatments
(e.g. bioremediation) and enhances directly or
indirectly the degradation rate of the pollutant
agent. Generally, the electroremediation
procedure is based on applying of a potential
difference between several electrodes distributed
in various configurations and positioned at
different distances onto the soil subjected to
ecological restoration in depth, thus creating an
electrical field. Under the action of the imposed
electrical field the contaminant agent is
mobilized due to the electrokinetic forces from
one electrode area towards the other one where it
is collected and then removed. Contaminants
migration under the action of an imposed
electrical field is done through electroosmosis,
electromigration and/or electrophoresis
processes. With this in view, the paper
presents some preliminary laboratory experimental
tests regarding the influence of some operating
parameters (applied potential, electrodes type,
electrodes distribution) on the degradation rate
of some organic compounds as contaminant agents
(e.g. phenol) with permanent recording of soil
water content, pH. Additionally, several aspects
dealing with the use of GIS technologies to
monitor both the pollution and restoration issues
as well as some preliminary information on a data
model generation able to collect and manage an
extended range of information that may be
spatially integrated are also discussed.
Experimental
There has been used sand of high porosity with 1
initial humidity and a pH of 8.67, as
experimental soil, with no further treatments,
weighting 3.23 kg, that has been artificially
polluted through addition of 300 cm3 of 0.5M
phenol aqueous solution. The experimental set-up
consisted in a soil cell, made of transparent
plastic with inner sizes of length 18 cm x width
14 cm x height 11 cm. Cilindrical graphite
electrodes of length 10 cm x diameter 8 mm have
been placed at a distance of 13 cm between them,
to generate the unidirectional electrical field.
The graphite electrodes have been introduced in
PVC perforated cylinders of 16 mm diameter,
covered by filter paper. The electrodes have been
connected at a DC power source of 0-60 V and the
voltage and the current were continuously
monitored. The soil bed with a volume of length
18 cm x width 14 cm x height 8.7 cm was prepared
for the test. There have been taken soil samples
after 16 hours, 25 hours, 41 hours, 58 hours of
treatment and pH, humidity and phenol content
have been determined. Soil pH was determined
using a soil-to-aqueous 0.1N KCl solution ratio
of 15, involving a 340i pH-meter (Germany). Soil
humidity has been determined through gravimetric
method. Phenol content has been evaluated
involving a modified potentiometric method
F.Huma, M.Jaffar, K.Masud, Turk.J.Chem.,
23(1999), 415-422, after phenol extraction from
the soil using methanol. The soil samples have
been taken from the vicinity of the anode,
cathode and from the middle of their distance, to
evidence the electromigration and electroosmotic
flow.
Results and discussion
The applied electrical field determined the
change of soil pH and humidity, as Figures 2 and
3 show. The following electrochemical reactions
at the electrodes take place -at the anode 2
H2O ? 4H O2(g) 4 e- -at the cathode 2 H2O
2 e- ? 2 OH- H2 (g) that significantly
influence the soil pH and further the direction
of electroosmotic flow and also the
sorption/desorption of the organic
pollutant. Thus, after 41 hours of electrical
treatment the soil pH near the anode dropped to
6.9 and near the cathode it increased to about 9
from the initial value of about 8.2. The soil
moisture decreased near the electrodes as
compared with the middle region. Under the
action of electrical field, the phenol content in
the anode region was reduced and it increased
towards the middle and cathode regions,
especially for the first 25 hours of electrical
treatment, which is also consistent with the
variation of current in time. After that,
however, it has been evidenced a relatively
contrary movement . Usually the phenol content
peak is placed in the middle region. These facts
suggest that the change of the soil pH in time
under the influence of electrical field may
produce a migration of the ionized phenol towards
the anode and thus a decrease of the
concentration around the cathode.
Figure 2 The change in soil pH under the effect
of dc electrical field
Figure 1 - Variation of electrical current with
time (electrical field of 4V/cm)
Figure 3 The change in soil moisture under the
effect of dc electrical field
The use of GIS technologies
Innovative accelerated in-situ remediation
technologies will be provided to decontaminate
(based on bacterial innoculus and electrokinetic
dispersion) soil and groundwater. Through
integration of the information provided by
software tools and remediation technologies,
elaboration of an assesment methodology of
cost-profit ratio and risk are in view, that are
significant for interested stakeholders
(scientific, industrial, public/administrative
ones) to build a definition framework for a best
practice in the field. In-situ remediation
technologies using direct currents with
electrodes placed on each side of the
Figure 4 The temporal v ariation of phenol in
soil under the influence of electrical field
Figure 5
contaminated soil separates and extracts the
organic contaminants form soils and
groundwater.The location of each electrode is
displayed in the site layout as-built drawing
contained in Figure 5. Software implementation
will use modalities that are similar to those met
in the specific reference European methodology,
integrating the application of geographical
information systems (GIS) through specialized
modules and the involvement of imagistic
controlling that will provide significant
information on the health state of a specific
area towards an interested authority and will
contribute to take strategical and tactical
decisions in order to prevent and to act by means
of planning, budgeting and monitoring of the
economical/social performance. The obtained
values of the indicators of soil and groundwater
oil pollution will be represented at territorial
scale , so that digital maps will be obtained on
their basis critical areas will be evidenced in
the case of pollution and the information
maintenance/updating will be kept in a spatial
database, a history of these interest values
being able to be built.. The concepts of the
technology are illustrated in Figure 6 and some
important aspects and design criteria of the
technology for field implementations are
presented.
Conclusions

• There have been evidenced the presence and action
  of the electroosmotic flow under the influence of
  the electrical field, materialized in a
  significant change of soil pH in the electrodes
  regions, that also affect the electromigration of
  phenol.
• The low content of moisture in the soil hinders
  the efficient migration of the pollutant agent
  towards electrodes and this may be the reason of
  the concentration of phenol in the middle region
  of the cell.
• Further detailed investigations will be performed
  for a deeper understanding of the processes and
  to optimize the technological parameters to
  achieve a better removal rate.

Figure 6

• The application of GIS provides a mean to
  integrate the various data layers involved in the
  organization, analysis and graphical display of
  the relationships between spatial and attribute
  data of critical variables and parameters, with a
  good potential for application in soil
  remediation issues, too.

Acknowledgements The presented experimental
activities are financially supported by the
Romanian Ministry of Education and Research,
PNCDI II Program under Research Contract
No.11036/2007