REMOVAL OF COPPER (CU) FROM MUNICIPAL SOLID WASTE (MSW) COMPOST USING BATCH WASHING

on the effect of compost use on heavy metal levels in the environment shows it to vary according to soil type, plant species and compost quality [2,3,4] . The presence of heavy metal ions in the environment has been of great concern because their toxic nature and other adverse effects on many life forms. For instance, excessive intake of copper results in an accumulation in the liver and it is also toxic to organisms [5]. Technologies available for treating metal contaminated sludge and soils include solidification/stabilization and vitrification. Recently, researchers try to develop soil washing techniques where soil -bound contaminants are transferred to the liquid phase by desorption and solubilization. Several washing solutions have been investigated such as water, acids, bases, chelating agents, alcohol and other additives. In practice, acid washing and chelator soil washing are two most prevalent removal methods [6]. EDTA is effective in removing metals from contaminated soils but the cost of EDTA is very high. Na2S2O5 is an inexpensive reducing agent, which has been extensively used to treat different metal contaminated waste. Abumaizar and Smith [7] studied on the batch and column washing of metals contam inated silky sand. They found that a mixture of

1 M Na2S2O5 and 0.01 M Na2EDTA provide an economically optimum solutio n for cadmium and zinc removal. Internat ional Scient ific Confer ence of Moder n Management of Mine Pr oducing, Geology and Environment al Pr ot ect ion SGEM 200 6 6th International Multidisciplinary Scientific GeoConference SGEM2006 www.sgem.org Int er nat ional Confer ence SGEM 200 6 92 The aim of the study was to practise soil washing techniques for removing Cu from MSW compost using the different concentrations of Na2EDTA solutions and the different concentration of mixture of Na2S2O5 (reducing reagent) and Na2EDTA (chelating reagent). The experiments were done in batch mode. MATERIALS AND METHODS Compost samples The compost samples were taken from Istanbul Solid Waste Recycling and Composting Plant in Kisirmandra, Istanbul. Fresh compost sample was dried at 105 °C for total Cu analysis and ground to yield 0.25 mm- sized particles. An approximately 1-2 g of this sample was weighed into an erlenmeyer. Digestion was performed by heating with a 10 ml-mixture of 1:1 (v/v) deionized water and nitric acid. After cooling, hydrogen peroxide, concentrated hydrochloric acid, and deonized water were added to the sample, and heated again. The cont ents were allowed to cool to room temperature, after which they were diluted with deionized water and passed through a 0.45 m filter, and processed on an atomic absorption spectrometer (UNICAM 929 AA spectrometer) for total Cu concentration determination [8]. Total Cu content in the sample (M) was calculated as mg/kg (dry weight) with the following equation: M = (CxV)/ m, where C is Cu concentration (mg/l), V is the final volume of the sample (liter), and m is the mass of the sample (kg). Total Cu amount in the compost used in the study is 348.6 mg/kg -dry compost. The maximum acceptabl e value of Cu in German standart s is 150 mg/kg -dry compost [9]. In this context, 57 % Cu removal yields should be obtained. Batch washing Five grams of dry sample was placed into a volumetric flask. Varying volumes and concentrations of washing solution were added into the sample. The sample was shaken horizontally at room temperature for 3 h at 160 rpm. After mixing, the aliquot was filtered through a 0.45 -µm membrane filter using vacuum filtration. Following the filtration, the filtrate was acidified to pH ≤2.0 with 1:1 HNO 3 for heavy metal analysis. Precision was established by preparing a replicate for each test. It was assumed that the metal concentration of the filtrat e represents the released from the compost. Removal efficiencies were determined by dividing the heavy metal release quantities by the initial quantity in the compost. Heavy metal analyses were performed using atomic absorption spectrometer (AAS) (UNICAM 929 AA spectrometer). RESULTS AND DISCUSSION Extractions with Na2EDTA Determination of the optimum Na2EDTA concentration Five grams of dry sample was placed into a volumetric flask. 30 ml of Na2EDTA solutions with varying concentrations were added into the sample. These samples were analyzed to determine the optimum Na2EDTA concentration. Results are shown in Table 1 and 2. Heavy metal removal efficiencies (%) for different concentrations of Na2EDTA are shown in Figure 1. SGEM 200 6 - Section I 93 Table 1. Cu amounts removed from the compost (mg/kg -dry compost) Concentrations (M) Cu

1 206.4 Table 2. Removal efficiencies obtained after extraction (%) Concentrations (M) Cu

1 59.2 Figure 1. Cu removal efficiencies (%) obtained for different Na2EDTA concentrations Upon examination of Figure 1, it was observed that increased removal yields for Cu were obtained with increased molarity of Na2EDTA solution . Figure 1 shows that the maximum removal efficienc y for 0.1 M Na2EDTA is 59% for Cu. Determination of the optimum solid:liquid ratio The optimum ratio was determined by addition of different amounts of 0.05 M Na2EDTA solution (1:2.5, 1:5, 1:12.5, 1:25). The samples prepared before were analyzed with this manner and the results are shown in Table 3 and 4. In Figure 2, heavy metal removal yields (%), obtained from different solid:liquid ratios, were shown. 6th International Multidisciplinary Scientific GeoConference SGEM2006 www.sgem.org Int er nat ional Confer ence SGEM 200 6 94 Table 3. Cu amounts removed from the compost (mg/kg -dry compost) solid:liquid ratios (g/ml) Cu 1:2.5 98.5 1:5 192.2 1:12.5 348.4 1:25 348.5 Table 4. Removal efficiencies obtained after extraction (%) solid:liquid ratios (g/ml) Cu 1:2.5 28.25 1:5 55.13 1:12.5 100 1:25 100 Figure 2. Heavy metal removal efficiencies (%) obtained for diff erent solid:liquid ratios As stated before, the increasing amount of Na2EDTA solution, which necessitates that the solid:liquid ratio goes lower, gives higher removal yields. Table 4 and Figure 2 shows that the 100% removal yield is reached. For Cu and Zn, the highest yield is present with a ratio of 1:12.5 . Studies performed with Na2EDTA and Na2S2O5 mixture Determination of the optimum solid:liquid ratio Experiments were carried out with 0.01 M Na2EDTA and 0.1 M Na2S2O5 mixture, with several solid:liqu id ratios. To 5 g of compost, several different volumes of this mixture were added and the samples prepared . They were analyzed to determine the SGEM 200 6 - Section I 95 optimum solid:liquid (g/mL) ratio. Results are shown in table 5 and 6. Figure 3 indicates Cu removal efficienci es (%), obtained for different solid:liquid ratios. Table 5. Cu amounts removed from the compost (mg/kg -dry compost) solid:liquid ratios (g/ml) Cu 1:2.5 121.44 1:5 225.2 1:6 348.3 Table 6. Cu removal efficiencies (%) obtained after extraction solid:liquid ratios (g/ml) Cu 1:2.5 34.8 1:5 64.6 1:6 100 Figure 3. Heavy metal removal efficiencies obtained for different solid:liquid ratios After the experiments, it is seen that decreasing the solid:liquid ratio increases Cu removal ratios. The highest removal ratio was obtained with 1:6 solid:liquid ratio (Cu: %100 ) (Fig. 3). Determination of the optimum concentration of the Na2EDTA and Na2S2O5 mixture The results of experiments to find the optimum concentration are presented in Tables 7 and 8. In Figure 4, Cu removal efficiencies (%) for different concentrations are shown. 6th International Multidisciplinary Scientific GeoConference SGEM2006 www.sgem.org Int er nat ional Confer ence SGEM 200 6 96 Table 7. Cu amounts removed from the compost (mg/kg -dry compost) Solutions Cu Solution 1 33.56 Solution 2 100.35 Solution 3 348.3 Solution 1: 0.001 M Na2EDTA and 0.1 M Na2S2O5 mixture Solution 2: 0.01 M Na2EDTA and 0.05 M Na2S2O5 mixture Solution 3: 0.01 M Na2EDTA and 0.1 M Na2S2O5 mixture Table 8. Cu removal efficiencies (%) Solutions Cu Solution 1 9.6 Solution 2 28.78 Solution 3 100 Solution 1: 0.001 M Na2EDTA and 0.1 M Na2S2O5 mixture Solution 2: 0.01 M Na2EDTA and 0.05 M Na2S2O5 mixture Solution 3: 0.01 M Na2EDTA and 0.1 M Na2S2O5 mixture Figure 4. Removal efficiencies obtained from experiments performed with several concentrations of Na 2EDTA and Na2S2O5 (%) After the experiments, the highest removal yield was obtained with 0.01 M Na2EDTA and 0.1 M Na2S2O5. The removal yields for this mixture is 100% (Fig.4). CONCLUSIONS Cu removal efficiencies increase with increasing chelator concentration. Further, as the solid:liquid ratio decreases, higher removal ratios are reached. After agitation for 3 hours at 1:25 solid:liquid ratio by using 0.05 M Na2EDTA, 100% removal yield was SGEM 200 6 - Section I 97 obtained. Literature suggests that sole chelator usage proves more costly, unless Na2S2O5 is included as the reducing reagent. Therefore, the optimum removal yield was obtained with 0.01 M Na2EDTA and 0.1 M Na2S2O5. 0.01 M Na2EDTA and 0.1 M Na2S2O5 provided more efficient removal than sole Na2EDTA usage at 0.05 M, which indicates that the solid:liquid ratio of the former is higher (i.e., less solution volume). 100% heavy metal removal yield was obtained with 0.01 M Na2EDTA and 0.1 M Na2S2O5, at 1:6 solid:liquid ratio. But in in German standarts, the maximum acceptable value of Cu is 150 mg/kg-dry compost, for this reason 57 % Cu removal yields should be obtained. It can thus be concluded that the mixture of 0.01 M Na2EDTA and 0.1 M Na2S2O5 mixture, at 1:5 solid:liquid ratio can conveniently be used to remove Cu from the compost. REFERENC ES

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