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Results and Discussion

Characteristics of the Samples

Table 12.1 shows SS, TOC, and pH in each sample. SS in the RL sample had a wide variation. Sediments in one of the two intake pits were moved to another pit during the pit maintenance between July and September; therefore, the turbidity in the pit in September was the highest, causing a wide variation of SS. More than 84 % of the SS in the RL was removed at the AR step, and then after the BT step, more than 93 % of the SS in the RL was removed. On the other hand, TOC was lowered after the MF step.

Table 12.1 Suspended solids (SS), total organic carbon (TOC), and pH in samples

Fig. 12.2 Element fractionation in the raw leachate (RL) sample

Element Fractionation in the Raw Leachate Sample

For the RL sample collected in December, concentrations of Co, Cs, Mn, Ni, and Sr were 13.4, 3.3, 1,810, 87.7, and 3,960 μg/L, respectively. The distribution of the element concentrations in each fraction were obtained as shown in Fig. 12.2. The filtration and ion exchange were carried out with good recovery ratios ranging from

94.6 % to 103 %. More than 82 % of the Co, Ni, and Mn was present in the particulate fraction. Mn exists as brown-colored Mn3O4 when it is incinerated at temperatures higher than 800 °C [8]. Because waste is generally incinerated above 800 °C and the color of the suspended solid was brown in the RL sample, Mn should be present as Mn3O4. Some Ni was in anionic form (9.5 %) and slightly more in cationic form (11 %). Ni is present as Ni2+ in the water environment [9], and it is also combined with organic matter [10, 11]. Organic matter has several functional groups such as phenolic, carboxyl, and carbonyl [12]. The leachate filtrate contained 13.8 mg/L dissolved organic carbon. Therefore, a part of the Ni in the leachate could be combined with dissolved organic matter and then exist in anionic form.

Cationic forms were dominant for Cs and Sr (Fig. 12.2). Most of the Cs and Sr would be present as Cs+ and Sr2+ under the pH and Eh conditions [9]. The principal form of Cs in municipal waste fl ash was suggested to be CsCl, which has high solubility [11]; this was attributed to the fact that the extraction ratios of Cs from fi e municipal waste fl ash samples ranged from 64 % to 89 % [13]. In contrast, extraction ratios of Cs from the municipal solid waste incinerator bottom ash and sewage sludge ash were less than 5.6 % and 2.7 %, respectively [13, 14]. Therefore, Cs in the leachate was from municipal waste fl ash, and the insoluble forms of Cs could not move downward with the leachate. For Sr, insoluble fractions were around 25 % in municipal waste fl ash and bottom ash and more than 40 % in sewage sludge ash [13], which implied that Sr in the leachate could originate from different types of waste.

Fig. 12.3 Element concentrations in samples at each treatment step. Error bars show the standard deviation of three replicates

 
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