Selection of alternative sorbent media contaminated groundwater clean-up

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1 Selection of alternative sorbent media contaminated groundwater clean-up for M. R. Boni & L. D Aprile Department of Hydraulics, Transportation and Roads, Rome, La Sapienza, Rome, taly University of Abstract Methods for the remediation of contaminated groundwater have focused, during the past years, on pump-and-treat and containment systems. Many experiences at contaminated groundwater sites and recent studies have shown the inadequacies of this approach and the need for new treatment technologies. The recent development of permeable barriers has presented a potentially viable alternative to conventional systems. Although zero-valent granular iron is the most commonly used reactive medium, a variety of media could be used to treat groundwater contaminants. This paper assesses possible alternatives to conventional sorbent media for metal removal from groundwater. The physicalchemical properties of two alternate materials (compost and expanded clay) were analysed and included particle size distribution, void ratio and dry density. Leaching test were conducted with two different methods, the first suggested by the talian regulation on solid waste and the secon~ TCLP, standardized by the U.S EPA, to assess the possible drawbacks of the investigated materials in terms of release of harmful substances. Batch testing was undertaken on the investigated materials to assess their sorption potential for cadmium and nickel. The experimental results show an high removal efficiency of the investigated materials in the tested concentration range, suggesting the possibility of a successful fill-scale application in a permeable barrier. ntroduction At many industrial sites unappropriatedplant management and uncontrolled waste disposal have led to widespread contamination of soil and groundwater. Groundwater remediation technologies usually involve extraction and subsequent treatment of contaminated water. Conventional pump-and-treat

2 458 Browttfield Sites: Assessment, Rehabilitation and De~elopntent systems could be used to capture and treat the plume. However, past experience at contaminated groundwater sites and recent studies have shown the limits of this approach. Also pump-and-treat systems would have to be operated for many years or decades, or as long as the source zone and the plume persist: the associated operation and manteinance costs over several decades can be enormous. Moreover this technolo~ is often inadequate to reach clean-up goals, since subsurface residuals frequently remain at undesirable levels, The recent research studies on Permeable Reactive Barriers (PRBs) have presented a potentially viable alternative to conventiomd pump-and-treat systems. These subsurface permeable treatment walls are being considered as a cost-effective in situ remediation technology. n its simplest form, a permeable reactive barrier consists of a zone of reactive material (such as granular iron, activated carbon, etc.) installed in the path of a contaminated plume. The main advantage of this system is that, generally, no pumping or aboveground treatment is required the barrier acts passively after the installation, without requiring an external energy source. Activated carbon is a material widely recognised for its sorption properties and is frequently used to remove aqueous phase organic contaminants. However, the use of activated carbon in permeable reactive wall applications can drive up the costs of this form of remediation. Because of this, alternatives to activated carbon have been investigated in order to establish materials with comparative sorptive properties (1). This paper presents the results of laboratory test that have been undertaken using two possible alternatives to activated carbon, compost and expanded clay. The characteristics of the investigated were analysed and included particle size distribution, void ratio and dry density. Leaching test were conducted with two different methods, the first suggested by the talian regulation on solid waste and the second, TCLP, standardized by the U.S EPA, to assess the possible drawbacks of the investigated materials in terms of release of harmful substances. Batch testing was undertaken on the investigated materials to assess their sorption potential for cadmium and nickel. The experimental results show an high removal efficiency of the investigated materials in the tested concentration range. However the results of the leaching test show potential drawbacks for the compost in terms of release of harmful substances, thus advising against a possible in situ application. Materials and methods Tha materials selected for analysis were: compost derived from the organic ffaction of MSW (supplied by a MSW treatment plant in taly) and expanded clay (Leca S.p.A, taly). The biological stability of the compost was evaluated through dynamic respirometric test. Three gramdometric fractions of expanded clay were chosen for the test: 8-16 mm, 2-4 mm, 0,125-0,25 mm. The main characteristics of the three fractions are reported in Table 1.

3 Browtzfield Sites: Assessment, Rehabilitation and De~ elopntent 459 Fraction Dry density Bulk density Void index Porosity (g/cm3) (g/cm3) (%) 8-16mm 0,292 2,554 7>746 88, mm 0,298 2,554 7,570 88,320 0,125-0,250 mm 0,812 2,554 2,145 68,196 Table 1: Main characteristics of the expanded clay ffactions Table 2 shows the main characteristics of the organic fraction compost. Table 2: Main characteristics of the organic fraction compost. Aqueous solution with the contaminants of interest (cadmium and nickel) and all the reagents for the leaching tests were prepared using all chemicals as received, Batch tests were conducted in 40 ml amber glass vials, Each vial, containing 3,8 g of solid (compost or expanded clay) was filled with 38 (solid/liquid ratio = 1:10) ml of the contaminated solution, and kept at constant agitation (KA KS 260, 300 rpm) until sampling time. The investigated initial concentrations were 5, 10, 20 mg/1 of cadmium and 20, 40, 80 mg/1 of nickel. Samples of the liquid for the analysis of the investigated metals were taken after 10, 30 rein, 1 h, 5 h, 24 h, 28 h, 27 h, 7 days, 10 days. The concentrations of metals in the samples from batch and leaching test were determined by Atomic Absorption Perkin Elmer 3030B. Leaching Tests Two different leaching tests were performed on the selected media. The first test is suggested by the talian regulation on solid waste (D,Lgs. 22/97, Decreto Ronchi, Appendix 3), performed in deionised water with sequential extractions; the second test, TCLP, Toxicity Characteristics Leaching Procedure is an EPA standard test performed in acid environment and usually applied in the United States for the chemical characterization of the reactive material used in PRBs, The results of both the leaching test methods performed on the organic fraction compost (Table 3) show concentration over the regulatory limits for iron, copper, manganese, nickel, lead and total chromium.

4 460 Browttfield Sites: Assessment, Rehabilitation and De~elopntent Leaching test suggested by the talian regulation (D.Lgs 22/97, Decreto Ronchi, Appendix 3) Sampling time Average concentration (m#l) Fe Cu Mu Ni Pb Cr 2h 7,75 4,17 0,50 0,58 0,27 1,08 8h 3,21 1,73 0,17 0,22 0,18 0,40 24 h 7,37 2,18 0,42 0,26 0,38 0,59 48 h 2,36 1,26 0,17 0,17 0,19 0,35 72 h 4,10 1,93 0,23 0,28 0,23 0, h 2,20 1,04 0,15 0,09 0,06 0,30 7d 1,62 0,95 0,12 0>07 0,19 0,19 16 d 3,30 0>37 0,26 0, ,20 Regulato~ 0,2 1 0,05 0,02 0,01 0,05 Limit (mg/1) TCLP Sample # Average concentration (mg/1) Fe Cu Mn Ni Pb Cr 1 2,11 1,27 4,22 0,27 0,36 0,38 2 2,96 1,40 4,24 0,26 0,36 0,45 3 1,87 1,53 4,15 0,25 0,34 0,39 Regulatory 0,2 0, ,05 0,02 Limit (mgll) Table 3: Results of the leaching test on the organic fkaction compost The same test performed on the three expanded clay fraction show concentration below the regulatory limits for the investigated metals (iron, cadmium, copper, zinc, manganese, nickel, lead, chromium). Sorption potential The sorption potential of the investigated materials for cadmium and nickel was evaluated using a linear approximation for the sorption isotherm (2): qc. L.ceK d m Where q, is the amount of solute sorbed onto the equilibrium concentration of the solute (mg/1) (1). solid (mg/g) and C is the

5 Brow field Sites: Assessment, Rehabilitation and De~>elopntent 46 ~ The distribution coefficient, h, represents the partitioning of the compound between liquid and solid. Retardation factors (?J were calculated using laboratory values for Q dry density and porosity and the following equation (l): R f =l+~dkd 0 where pdis the dry density and 8 is the porosity. Figures 1, 2 and 3 show the trend of the concentration of cadmium in solution versus time for the investigated fractions of expanded clay (8-16 mm, 2-4 mm, 0,125-0,25 mm). Figure 4 shows, as an example, the linear approximation for the sorption isotherm of the 8-16 mm fraction, The values of Q and Rfare reported in Table 4. Figures 5 and 6 show the results related to the concentration of cadmium in solution versus time and the linear approximation for sorption isotherm for the organic fraction compost ~ i = g Q A 05 mgll 10 mgll 5 \ A20 mg/1 D CJO t(rein) Figure 1: Concentration of Cd in solution versus time (expanded clay, 8-16 mm)

6 462 Browttfield Sites: Assessntent, Rehabilitation and De~elopntent ~ 5 g o 10 5 \ o U i t(rein) Figure 2: Concentration of Cd in solution versus time (expanded clay, 2-4 mm) ~ 14 t = ~ 12 E r ~m 05~n Omgfl A20 mgil :~ o 20C c t(rein) Figure 3: Concentration of Cd in solution versus time (expanded clay, 0,125-0,25 mm)

7 Browtzfield Sites: Assessntent, Rehabilitation and De~ elopntent 463 0,035, s y = 0,0004X R2=0,8S17 0,02- g ~ 0,015- x + + A ~ 0,01-0,005- } o Ceq (mg/1) Figure 4: Linear approximation for the sorption isotherm of the 8-16 mm fraction of expanded clay for Cd 20,00 15,00 ~! g u 10,00! L--l 05 mgll 1Omg/1 A20 mg/! 5,00 1 0,00 A o t (rein) Figure 5: Concentration of Cd in solution versus time (organic fraction compost)

8 464 Browttfield Sites: Assessntent, Rehabilitation and De~elopntent 1 0,9 0,8 0,7 0,6 0,4 0,3 0,2 0, ,5 1 1,5 2 2,5 3 3,5 4 4,5 Ceq Figure 6: Linear approximation for the sorption isotherm of the organic fraction compost for Cd Material & Rf Compost 0, ,50 Expanded clay (8-16 mm). 0,0004 1,13 Expanded clay (2-4 mm). 0,0009 1,30 Expanded clay (0,125-0,25 0, ,05 mm). Table 4: Obtained values of & and Rffor expanded clay and organic fraction compost with Cd The obtained values of & and Rf for expanded clay and organic fraction compost with nickel as a contaminant are reported in Table 5. Material b\rf Compost 0, ,59 Expanded clay (8-16 mm). 0,0003 1,01 Expanded clay (2-4 mm). 0,0031 2,04 1 Expanded clay (O,125-0,25 10,004816,71 mm). Table 5: Obtained values of & and Rffor expanded clay and organic fraction compost with Ni

$Browtzfield Sites: Assessntent, Rehabilitation and De~ elopntent 465 Conclusions The aim of the performed test was to investigate the sorption potential of expanded clay and organic fraction compost$

9 Browtzfield Sites: Assessntent, Rehabilitation and De~ elopntent 465 Conclusions The aim of the performed test was to investigate the sorption potential of expanded clay and organic fraction compost as alternatives to activated carbon. The results of batch test show an high removal efficiency for the organic fraction compost and for the smaller fraction of the expanded clay (O,125-0,25 mm). However the values of h and Rf (Table 4 and 5) show a lower adsorption potential when nickel was chosen as a contaminant of interest. The effect of particle size is particularly evident in the case of expanded clay with an increasing of the adsorption rate when the particle size decrease. This is due to the fact that the surface area increases with decreasing particle size (3). The effect of the initial concentration in solution has a clear effect only in the results of the test performed on the larger fraction of the expanded clay (see Figure 1) in which the adsorption rate is slower. Even if the organic fraction compost seems to have better sorption properties (higher retardation factor) if compared to the expanded clay, even in the smaller fraction, the results of the leaching test show some environmental drawbacks for this material due to the potential release of harmfhl metals (copper, manganese, nickel, lead and total chromium) in solution, thus indicating more usefid applications, in permeable reactive barriers, for the expanded clay. References [1] Parker, F., Smith D.W., Hitchcock P.W., The use of alternatives to activated carbon for the clean up of contaminated groundwater, Proceedings of Geoeng 2000, Melbourne (Australia), 2000 [2] Hinz, C. Description of sorption data with isotherm equations, Geoderma 99, pp ,2001 [3] Mellah, A., Chegrouche, S., The removal of zinc from aqueous solutions by natural bentonite, Wat.Res. Vol. 31, n03, pp , 1997

8.1 Introduction 8.2 Summary 8.3 Conclusion. Contents

Summary and Conclusion Contents Chapter 8 SUMMARY AND CONCLUSION 8.1 Introduction 8.2 Summary 8.3 Conclusion 8.1 Introduction In landfills without liners between the waste and the underlying geology or