Yeliz Yukselen-Aksoy

Sequestration of heavy metals in soils from two polluted industrial sites: implications for remediation

This study was conducted to determine the distribution of heavy metals in two different contaminated field soils, and to assess its influence on remedial performance. The two field soils were obtained from two different polluted industrial sites in the Metropolitan Chicago area and were characterized for physical and chemical properties. The soils were referred to as silty sand and silty clay, based on their particle-size distribution. A five-step sequential liquid–solid extraction procedure was used to speciate the heavy metals into: (1) easily exchangeable; (2) carbonate bound; (3) Fe/Mn oxide bound; (4) organic bound; and (5) residual fractions. These results showed that all the metals except mercury were predominantly distributed as the Fe/Mn-bound form in silty sand. In contrast, they were distributed as the residual form in silty clay. Results indicated that the metals in both soils were in the forms that are not easily amenable to soil washing using water. Therefore, batch extraction tests with varying concentrations of ethylenediaminetetraacetic acid (EDTA) (0.05, 0.1 and 0.2 M) and acetic acid (0.5, 0.1 and 2 M) were conducted to identify an optimum soil-washing-based remediation system for both silty sand and silty clay. Ethylenediaminetetraacetic acid was found to be effective for the remediation of silty sand, while acetic acid was found to be suitable for the removal of metals that existed in residual form in silty clay. Based on these results, total removal efficiency was found to follow the order: sand + EDTA > clay + acetic acid > sand + acetic acid > clay + EDTA. This study showed that the speciation and remediation of heavy metals in soils depend on the sitespecific soil composition, and this should be carefully considered in the selection of an efficient remedial method.

Electrokinetic Delivery and Activation of Persulfate for Oxidation of PCBs in Clayey Soils

Contamination of soils by polychlorobiphenyls (PCBs) is of environmental concern because of their toxicity, persistence, hydro- phobic nature, and slow biodegradation potential. Among the PCB remedial technologies, direct oxidation by persulfate is considered to have great potential to be both simple and rapid. However, to produce faster reaction rates, persulfate is often activated using heat, metal chelates, hydrogen peroxide, or high pH. Furthermore, delivery of persulfate in low permeability clayey soils is difficult. Integrating electrokinetic re- mediation with persulfate has the potential to overcome such difficulties because the applied electric potential can facilitate the delivery of per- sulfate in low permeability soils as well as activate oxidizing radicals and simultaneously induce oxidative/reductive reactions directly in the soil.ThisstudyinvestigatesthepotentialforinsituoxidationofPCBsinlowpermeabilitysoilsusingpersulfateasanoxidantandalsoevaluates the benefits of integrating oxidation with electrokinetic remediation. Several series of laboratory batch and bench-scale electrokinetic experi- ments were conducted using kaolin, a representative clayey soil, spiked with 50 mg/kg of 2,2 0 ,3,5 0 tetrachlorobiphenyl (PCB 44), a represen- tative PCB. Persulfate oxidation activators (elevated temperature (45� C) and high pH (at the cathode)) were investigated to maximize the PCB degradation. In addition, the effect of oxidant dosage on PCB degradation was investigated. The electrokinetically enhanced temperature-only activated persulfate oxidation test resulted in better PCB 44 remediation (77.9%) than the temperature and high-pH activated persulfate oxidation(76.2%)ina7-dayperiod.Theoptimaldosageforeffectiveremediationwas30%Na-persulfate(76.2%)becausea20%concentration of the oxidant yielded a lower rate of degradation (55.2%) of PCB 44. The results are encouraging for the use of electrokinetically enhanced persulfate oxidation for the effective remediation of PCBs in soils.DOI:10.1061/(ASCE)GT.1943-5606.0000744.

Effects of biochar amendment on geotechnical properties of landfill cover soil

Biochar is a carbon-rich product obtained when plant-based biomass is heated in a closed container with little or no available oxygen. Biochar-amended soil has the potential to serve as a landfill cover material that can oxidise methane emissions for two reasons: biochar amendment can increase the methane retention time and also enhance the biological activity that can promote the methanotrophic oxidation of methane. Hydraulic conductivity, compressibility and shear strength are the most important geotechnical properties that are required for the design of effective and stable landfill cover systems, but no studies have been reported on these properties for biochar-amended landfill cover soils. This article presents physicochemical and geotechnical properties of a biochar, a landfill cover soil and biochar-amended soils. Specifically, the effects of amending 5%, 10% and 20% biochar (of different particle sizes as produced, size-20 and size-40) to soil on its physicochemical properties, such as moisture content, organic content, specific gravity and pH, as well as geotechnical properties, such as hydraulic conductivity, compressibility and shear strength, were determined from laboratory testing. Soil or biochar samples were prepared by mixing them with 20% deionised water based on dry weight. Samples of soil amended with 5%, 10% and 20% biochar (w/w) as-is or of different select sizes, were also prepared at 20% initial moisture content. The results show that the hydraulic conductivity of the soil increases, compressibility of the soil decreases and shear strength of the soil increases with an increase in the biochar amendment, and with a decrease in biochar particle size. Overall, the study revealed that biochar-amended soils can possess excellent geotechnical properties to serve as stable landfill cover materials.

Suction characteristics of compacted zeolite-bentonite and sand–bentonite mixtures

Soil suction is one of the most important parameters describing soil moisture conditions for unsaturated soils used in landfill liners. However, few studies have been conducted on the suction characteristics of compacted zeolite–bentonite mixtures (ZBMs) and sand–bentonite mixtures (SBMs), which are proposed for use as liner materials. Nevertheless, zeolite is known for its microporous skeleton containing cages and tunnels and it has a great physical affiliation to water uptake. Zeolite and bentonite, in a mixture, are thought to be in competition for water uptake and this may alter the distribution of water content for each soil in the mixture. The present study investigated the suction properties of compacted ZBMs and SBMs for varying mixing ratios and compaction water contents. The soil suction measurement technique chosen was the filter-paper method. The suction characteristics of powdered, granular, and block zeolites, as well as 0, 10, and 20% bentonite in ZBMs and SBMs were measured and compared with each other. Contaminated compacted ZBMs are compared with those of uncontaminated compacted ones at the optimum water content for the 10% and 20% mixtures. The results show that suction capacity of zeolite increases with grain size. As bentonite content increases, both matric and total suction increase for both mixtures. ZBMs have higher matric suction values than SBMs, but not total suction values. Contaminated total suction values are found to be higher than those of uncontaminated samples due to an increase in dissolved ion concentration.

The effect of soil mineralogy and pore fluid chemistry on the suction and swelling behavior of soils

Soil suction is one of the most important parameters for describing the moisture condition and engineering behavior of unsaturated soils. Therefore, changes in suction behavior of soils in the presence of saline waters are important for engineered barriers. The aim of this study was to determine the change in suction and swelling behavior of soils, which were exposed to salt solutions (NaCl, CaCl2, natural seawater) with respect to distilled water. The three soil samples were gathered with different mineralogy and plasticity characteristics and tested for determining matric and total suction values and for obtaining free swelling characteristics in the presence of salt solutions. The bentonitic soil sample had the highest total suction value in the presence of seawater. Kaolinitic and zeolitic soil samples had the highest total suction values in the presence of NaCl solution. The highest modified free swell index value of the samples was obtained in the presence of NaCl solution for all the soil samples. No relationship was found between the total suction, matric suction and the modified free swell index value of the tested soils.

Compaction behavior of synthetic and natural MSW samples in different compositions

Compaction is the one of the most important stages of the storage process in landfills. Well-compacted municipal solid waste (MSW) occupies less volume than an uncompacted MSW sample of the same weight and provides a safer storage area. The composition of MSW changes in between countries and even cities. For that reason, for effective compaction, the composition effect should be investigated. In this study, effects of composition, degradation and energy on the compaction behavior of artificially-prepared and natural fresh and aged MSW samples were determined. Artificial samples were prepared in representative different compositions Europe (E-1), Turkey (T-1) and the USA (U-1) to examine the effect of the composition. In addition to the synthetic MSW samples, natural MSW samples were obtained from the municipal landfill area of Manisa, Turkey. The standard Proctor test results have shown that the highest maximum dry unit weight was observed with the U-1 composition, which has the lowest organic content and the highest metal content. The degradation effect was investigated on the natural samples. The degraded MSW sample (3–4 years) has significantly higher maximum dry unit weight than the fresh natural MSW sample because of its low organic content. According to the results of this study, with respect to the composition effect, the percentage of organic waste is the most important factor on the compaction behavior of MSWs. As paper, organic and plastic contents increase in the MSW composition the γdry-max value decreases and wopt increases. The ash content does it reversely, as such that any increase in γdry-max decreases the wopt value of the MSW.

The Effects of Colemanite and Ulexite Additives on the Geotechnical Index Properties of Bentonite and Sand-Bentonite Mixtures

Bentonite-sand mixtures are generally used in landfill liners. The properties of bentonite-sand mixtures should not change by time. For that reason, it is necessary to improve the properties of bentonites and bentonite-sand mixtures. In this study, the boron minerals namely colemanite and ulexite were added to the bentonite and bentonite-sand mixtures in order to improve their consistency limits and compaction characteristics. The boron additives were added 5, 10, 15, 20% to the bentonite and the liquid limits and plastic limits were determined. The boron additives were added to the 10% bentonite + 90% sand and 20% bentonite + 80% sand mixtures and compaction characteristics were determined in the presence of colemanite and ulexite.

Influence of Seawater on the Suction and Swelling Behavior of Clayey Soils

The present study examines the suction characteristics and swelling behavior of clayey soils when exposed to natural seawater with respect to distilled water. The effects of saline waters on the engineering behavior of soils need to be determined since the salinity of the pore fluid of soils near coastal areas increases continuously. Six clayey soil samples with different mineralogy and characteristics were gathered and tested to determine the suction and swelling characteristics in the presence of natural seawater and distilled water. The results show that the total suction values of the samples are higher in the presence of seawater than in distilled water. The samples with high swelling potential have lower matric suction values than nonswelling soils. Moreover, in contrast to swelling-type soils, the matric suction values of the nonswelling soils remain similar in the presence both distilled water and seawater. The modified free swell index (MFSI) of the samples is well correlated with the liquid limit (LL), plasticity index (PI), and cation exchange capacity (CEC) in distilled water. However, coefficients of determination decreased in the presence of seawater. Also, there is no significant correlation existing between total and matric suction values and the MFSI values of the samples.

Discussion of “Swelling characteristics of bentonite in artificial seawater”Appears in Canadian Geotechnical Journal, 46(2): 177–189.

The authors have to be congratulated for presenting such interesting research. The results are important not only in terms of buffer material to fill disposal facilities, but also in terms of understanding the effect of rising seawater level and regression of seawater inland due to excessive fresh water withdrawal at coastal areas (Yukselen et al. 2008). Thus, the discussers are very interested in the results presented in this paper, and would like to offer the following comments on the authors’ interpretations. The experimental results reveal that the maximum swelling pressures of bentonites B–E are affected by artificial seawater to varying degrees. However, results are obscure for several reasons. For example, it is known that calciumtype bentonite has lower swelling potential than sodiumtype bentonite under the same testing conditions (Azam et al. 2000). However, the comparison of maximum swelling pressures shown in Fig. 6 indicates that the maximum swelling potential of calcium-type bentonite yields a larger swelling pressure than sodium-type bentonite. Furthermore, even though the other sodium-type bentonites (B, D, E) are affected by artificial seawater, bentonite A is not affected. These results from Fig. 6 are also in apparent contradiction with Figs. 9 and 12. For example, the maximum swelling strain difference between distilled water and artificial seawater is negligible for bentonite C. On the other hand, there are appreciable strain differences in bentonite A. We wonder if the presented maximum swelling pressures of the bentonites are merely a function of the water content of the samples. To this end, we plotted the maximum swelling pressure of bentonites as a function of their average water content (Fig. D1). We also plotted the maximum swelling pressure as a function of the montmorillonite content of bentonites (Fig. D2). As seen from Fig. D1, the swelling pressure of bentonites increases linearly with average water content, implying that the reported maximum swelling pressures are also a function of moisture content. In conclusion, the results show that the maximum swelling pressure of bentonites appears to increase concomitant with montmorillonite and water contents (Fig. D2). This should be expected as the listed average water content is a function of the montmorillonite content (Fig. D3). We believe that the reported swelling pressures of bentonites are a coupled function of their water and the montmorillonite content. Thus, from the presented data it is hard to reach the conclusion that the ‘‘influence of artificial seawater on the swelling characteristics of sodium-type and artificial sodium-type bentonites is low’’ and ‘‘the influence of artificial seawater on swelling characteristics of calcium-type bentonite is more slight than sodium-type and artificial sodium-type bentonites.’’ Further evidence of the above statements is the variation of maximum swelling pressures with liquid limit. As seen from Fig. D4, the swelling pressure decreases with an increase in the liquid limit of bentonites. This appears to contradict previous research that documents swelling pressures that increase (not decrease) with an increase in liquid limit of soils (Vijayvergiya and Ghazzaly 1973; Chen 1988; Issa 1997). Additional evidence of the above stated statement comes from the authors’ own data. For example, if we take the maximum swelling strain differences between distilled water and artificial seawater at 1.4 Mg/m3 of initial density under 10 kPa vertical pressure and plot them as a function of the liquid limit of bentonites, the maximum swelling differences increase with an increase in liquid limit (Fig. D5). We chose the initial dry density of 1.4 Mg/m3 as this density is the only initial density in all tested samples. We validate our observations by plotting the observed maximum swelling strains presented in Fig. 9 as a function of the liquid limit of samples at 1.65 Mg/m3. As seen from Fig. D6, the observed maximum swelling strain is a function of liquid limit. We would appreciate the authors’ comments on our interpretation of the reported results.