MITIGATION MEASURES FOR CHROMIUM-VI CONTAMINATED GROUNDWATER AND SOIL USING ZERO VALENT IRON TECHNOLOGIES

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1 Proceedings of the 13 th International Conference on Environmental Science and Technology Athens, Greece, 5-7 September 2013 MITIGATION MEASURES FOR CHROMIUM-VI CONTAMINATED GROUNDWATER AND SOIL USING ZERO VALENT IRON TECHNOLOGIES LILLI* M.Α., NIKOLAIDIS* N.P, KARATZAS* G.P., KALOGERAKIS* N. and MUELLER** M. *Department of Environmental Engineering, Technical University of Crete, Polytecneioupolis, Chania, Greece. **FMC Environmental Solutions, Brussels, Belgium EXTENDED ABSTRACT The contamination problem of the Asopos River is multi-dimensional. It involves drinking water with concentrations of Cr(VI) above the acceptable criteria, river contamination with concentrations above aquatic quality standards, irrigation with groundwater that contains hexavalent chromium and accumulation of chromium in top soils. Lack of wastewater treatment facilities and lax enforcement of environmental laws have resulted in direct disposal of chrome containing effluents in surface and groundwater bodies. The aim of the study is to evaluate zero valent iron (ZVI) technologies for in situ groundwater treatment and chromium stabilization in soils and sediments. Within the framework of the LIFE project CHARM (Chromium in Asopos Groundwater System: Remediation Technologies and Measures), the Technical University of Crete in collaboration with FMC used a very efficient pump and treat method for removing chromium from groundwater using ZVI. Two pilot units have been designed to treat contaminated groundwater from chromium in the area of Oinophyta. In this method, iron is oxidized by the water and in turn hexavalent chromium is reduced to trivalent which precipitates in solution or on the iron surfaces. The ZVI filter is followed by an iron removal filter in order to remove the iron exported by ZVI. The first phase involved laboratory experiments to determine the design parameters of the pilots for the particular groundwater matrix (i.e., hydraulic retention time, ZVI/sand ratio, loading rates, removal rates etc) and the second phase involved large-scale field experiments using two types of ZVI (Connelly and Rio Tinto). Stabilization of chromium in sediments and soils experiments were conducted using three different ZVI-based products (Connelly s ZVI, EHC, and DARAMEND ). Six different ZVI-to-soil ratios were used in batch experiments to determine the efficiency of Cr stabilization. Both column studies and stabilization experiments showed that ZVI can efficiently remove hexavalent chromium from solution or stabilize it on soils and sediments. Stabilization studies confirmed that the ZVI, EHC and DARAMEND can reduce the leachability of hexavalent chromium by 70% using only 0.25% of the product. KEYWORDS: groundwater treatment, soil stabilization, zero valent iron technologies, hexavalent chromium 1. INTRODUCTION The mobilization of pollutants from their natural reservoirs to the atmosphere, soil and water is one of the most important negative impacts of human activities on terrestrial and aquatic ecosystems (Koptsik et al., 2003). The last decades has seen an increasing research interest on groundwater and soil contamination by heavy metals. Chromium is one of the toxic heavy metals that has been in the center of such investigations. Chromium is named for the many colors exhibited by its compounds (Shupack, 1991), and has nine oxidation states ranging from -2 to +6. However, in the environment, Cr is found in two oxidation states, Cr(III) and Cr(VI). Hexavalent Cr is mobile and highly toxic for humans, whereas Cr(III) is immobile, has low toxicity and is considered to be an

2 essential trace element for human metabolism. The above differences of the two oxidation states of chromium make the assessment of potential human health risks, difficult (James, 1996). Directive 98/83/EC has established 50 ppb as the maximum limit of total chromium in drinking water, similar to limit established by the World Health Organization (Oze et al., 2007). The limits established by The EC, USA and the WHO do not differentiate between the two oxidation states, however certain country members such as Italy do. The Italian regulation (D.M. 25 October 1999, no. 471) imposed a maximum acceptable concentration of only 5 ppb for Cr(VI) in groundwater, and of 2 ppm (on a dry basis) for Cr(VI) in soils for private and residential use, and a maximum acceptable concentration of 150 ppm for total Cr (Fantoni et al.,2002). The assessment of contaminant mobility is a necessary tool so as to establish either riskbased or mobility-based, site-specific cleanup levels of remediation (Nikolaidis and Shen, 2000). Remediation of chromium-contaminated soils and groundwater can be achieved by many physical, chemical and biological treatment technologies. Physical technologies include: free product recovery, pump- and- treat, soil vapor extraction, air sparging, groundwater circulation wells, soil heating etc. Chemical technologies include: precipitation, stabilization, electrochemical processes, adsorption and ion exchange, soil washing etc, and finally biological processes include: biosparging, biological reactors, anaerobic and aerobic biotransformation etc. (ASCE, 2007). The use of zero valent iron (ZVI) to remove chromium, and other heavy metals, is a promising technology that has the potential to remediate in a cost effective way impacted ground-waters and soils. This treatment technology takes advantage of the chemical reactions at the surface of ZVI which is capable of transforming or degrading contaminants into non-toxic or immobilized chemical (Powell et al., 1995). Asopos river basin presents a serious chromium contamination problem as the concentrations of Cr(VI) in surface water are above the acceptable criteria and groundwater quality in many areas exceed the quality standards. Therefore there are potential negative effects for human health, the environment and the agricultural production (Moraetis et al., 2012). The objective of this study is to evaluate zero valent iron (ZVI) technologies for in situ groundwater treatment and chromium stabilization in soils and sediments in the area of Asopos. Within the framework of the LIFE project CHARM (Chromium in Asopos Groundwater System: Remediation Technologies and Measures), the Technical University of Crete in collaboration with FMC used a very efficient pump and treat method for removing chromium from groundwater using ZVI and proposed a stabilization process for soil remediation, that is applicable to field operations, taking into account the quantity of the method and the cost of the technology. 2. METHODOLOGY 2.1 Water treatment technology for chromium removal The groundwater treatment technology of chromium removal by iron filings necessitates pumping of ground water above ground and treating it prior to reinjection or for use in irrigation/drinking water. This technology uses iron filing filters (Zero Valent Iron, ZVI), where iron is being oxidized by the water and in turn hexavalent chromium is reduced to trivalent which precipitates in solution and/or adsorbed onto the iron surfaces. The demonstration of this technology in the area of Oinophyta was conducted in two phases. The first phase consisted of a laboratory column study to determine the design parameters of the pilot plants for the particular groundwater matrix (i.e., hydraulic retention time, ZVI/sand ratio, loading rates, removal rates etc) and to evaluate two different types of ZVI (Connelly s ZVI and ZVI from Rio Tinto) for their effectiveness in removing chromium from the solution. The chemical composition of Connelly s ZVI and ZVI from Rio Tinto (H 2OmetTM 58) are presented in Table 1 and 2, respectively. The flow rate was varied in order to obtain different retention times. Iron and chromium

3 concentrations of the effluent solution were determined by ICP MS (Agilent CX).The removal efficiencies were estimated for each condition and the results were used in the design of the large scale pilot. The laboratory studies were used as a tool for scaling up. The second phase included the construction of the two pilot plants. The pilots are comprised of a ZVI/sand filter, an aeration unit (to oxidize the ferrous iron to ferric) and a sand filtration unit to remove the exported iron. The large scale pilot was designed to treat 10 m 3 /d of chromium contaminated groundwater, using Connelly s ZVI, and the small scale pilot was designed to treat 1 m 3 /d of chromium contaminated groundwater, using ZVI from Rio Tinto. Table 1. Chemical analysis of Connelly s ZVI (wt%) C S P Mn Si Cu Fe Table 2. Chemical analysis of ZVI from Rio Tinto (H 2OmetTM 58) (wt%) C O S P Mn Si V Ti Cu Fe > Soil and sediment treatment technology for chromium removal The stabilization studies included batch experiments that were conducted in order to study the effectiveness of ZVI and other ZVI based technologies in reducing the amount of chromium released from sediment. Three sediment samples from the area of Asopos river were used. Specifically one sample was from the area of Erythres (sd5), one from Agios Thomas (sd7) and one from Oropos (sd8), that are representative of all surface geological formations and cover the entire basin of Asopos river. Stabilization of chromium in sediments and soils experiments were conducted using three different ZVIbased products (Connelly s ZVI, EHC, DARAMEND ). The EHC and DARAMEND products provided by FMC Environmental Solutions company and their physical and chemical properties are presented in Tables 3-4. Six different ZVI-to-soil ratios were used in batch experiments to determine the efficiency of Cr stabilization. Heavy metals and total chromium of the solution were determined by ICP MS (Agilent CX). Table 3. Physical and chemical properties of EHC PHYSICAL AND CHEMICAL PROPERTIES OF EHC Appearance Tan / brown flakes Odour odourless Boiling point 3000 o C Melting/Freezing point o C Specific gravity O.75 Solubility insoluble Vapour pressure 1787 o C Table 4. Physical and chemical properties of DARAMEND PHYSICAL AND CHEMICAL PROPERTIES OF DARAMEND Appearance Tan / brown flakes Physical state solid ph 6.0 Flammable properties Combustible material Density 0.97 kg/l

4 3. RESULTS 3.1 Laboratory results for filter design parameters The results of the column experiments for the two types of ZVI and the two flow rates are presented in Figs 1 and 2 for chromium and iron respectively. Each column was run for 24 hours using a flow rate of 7 ml/min and then the flow rate was reduced to 3.5 ml/min. The results showed that Connelly's ZVI was very effective in chromium removal as the initial concentration (300 μg/l) within 3 hours was almost reduced to zero (Fig. 1). A small increase after 24 hours was normal due to the change in flow rate and within an hour the concentrations were reduced to ppb levels. The Fe export from the Connelly column was significant from the beginning of the experiment. Fe increased with time reaching steady state after 24 hours and concentration of 2.3 mg/l (Fig. 2). Regarding the ZVI from Rio Tinto the results were slightly different. There was no iron export from the column suggesting that ZVI corrosion had not been initiated during the experiment. Chromium removal was satisfactory during the first 10 hours of the experiment (possibly due to adsorption to iron oxides) and then increased to 150 ppb and reduced slightly was the flow rate was decreased. This is a typical phenomenon for some types of ZVI that require some initial pretreatment with acid for activation. Even at this stage, the Rio Tinto ZVI reduced the Cr concentration from 300 mg/l to 80 mg/l which corresponds to 73% removal. It is expected that within a few days of continuous use of the filter, the Rio Tinto ZVI will achieve efficiencies similar to Connelly's. Figure 1. Cr concentrations in the output of the column using ZVI and ZVI from Rio Tinto Figure 2. Fe concentrations in the output of the column using ZVI and ZVI from Rio Tinto

5 3.2 Stabilization of chromium in Asopos sediments The results of the stabilization experiments using Connelly's ZVI, DARAMEND and EHC for 8 ZVI to soil ratios are presented in Figs. 3-5 respectively. Chromium leachability was reduced exponentially with the increase in ZVI content for all three products. Fig. 6 presents a comparison of the 3 products for 0% and 1% ZVI. The results showed that Connelly's ZVI, DARAMEND and EHC can reduce the leachability of hexavalent chromium by 78%, 82% and 94% respectively, using only 1% of the product. EHC was shown to be the most efficient in Cr(VI) stabilization. Figure 3. Stabilization of chromium in sediment sd8 at different ZVI/soil ratios Figure 4. Stabilization of chromium in sediment sd8 at different DARAMEND/soil ratios Figure 5. Stabilization of chromium in sediment sd8 at different EHC/soil ratios

6 Figure 6. Comparison of the 3 ZVI-based products in chromium leachability 4. CONCLUSIONS ZVI was shown to be an effective product that can be used to remove Cr(VI) for ground water and stabilize it on contaminated soils and sediments. Regarding the water treatment studies, the results showed that Connelly's ZVI was very effective in chromium removal as the initial concentration (300 μg/l) was almost reduced to zero over time. ZVI from Rio Tinto was also efficient in chromium removal however, it requires an initial activation period. Regarding sediment and soil treatment studies, the results showed that Connelly's ZVI, DARAMEND and EHC can reduce the leachability of hexavalent chromium by 78%, 82% and 94% respectively, using only 1% of the product. REFERENCES 1. ASCE, Remediation technologies for soils and groundwater. Edit: Bhandari, A., Surampalli, R.Y., Chanpagne, P., Ong, S.K., Tyagi, R.D., Lo, I.M.C. EWRI 2. Fantoni, D., Canepa, Ζ. M., Cipolli, Ζ. F., Marini, Ζ. L., Ottonello, G., Zuccolini, Ζ. M.V., Natural hexavalent chromium in groundwaters interacting with ophiolitic rocks. Environmental Geology, 42, James, B.R., The challenge of remediating chromium-contaminated soil. Environmental Science and Technology, 30, Koptsik, S., Koptsik, G., Livantsova, S., Eruslankina, L., Zhmelkova, T., Vologdina, Z., Heavy metals in soils near the nickel smelter: chemistry, spatial variation, and impacts on plant diversity. J. Environ. Monit., 5, 3, Moraetis, D., Nikolaidis, N.P., Karatzas, G.P., Dokou, Z., Kalogerakis, N., Winkel L.H.E, Palaiogianni-Bellou, A., Origin and mobility of hexavalent chromium in North-Eastern Attica, Greece. Applied Geochemistry, Volume 27, Issue 6, Nikolaidis, N.P., Shen, H., Conceptual site model for evaluating contaminant mobility and pump and treat remediation. GNEST Int. J. 2, Oze, C., Bird, D.G., Fendorf, S., Genesis of hexavalent chromium from natural sources in soil and groundwater. Proceedings of the National Academy of Sciences of the United States of America 104,16, 6544e Powell, R.M., Puls, R.W., Hightower, S.K., Sabatini, D.A., Coupled iron corrosion and chromate reduction: mechanisms for subsurface remediation. Environ. Sci. Technol., 29, Shupack, S.I., The Chemistry of Chromium and Some Resulting Analytical Problems. In: Environmental Health Perspectives. NIH Publication, 92,