Motivation

1. ELECTROKINETIC REMEDIATION OF CONTAMINATED SOILS AND POLLUTION MONITORING INVOLVING GIS TECHNOLOGIES Ovidiu Anicăi1, Roxana Dumitrache2, Mihai Duţu2, Constantin Ana2 1Institute for Computers – ITC SA, Calea Floreasca 167, Sector 1, Bucharest, oanicai@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 sandof 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 1:5, 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