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Many studies have focused on heavy metal characteristics in sewage sludges and sludge-amended soils other than lime-stabilized sewage sludge (LS). Thus, the aerobically digested sewage sludge cake (13.61 % solids) sampled from the Min-Sheng Wastewater Treatment Plant in Taipei City, Taiwan was lime-stabilized for studying the effects of the lime treatment on fractionation and extractabilities of heavy metals (Cu, Pb, Cr, and Zn) in sewage sludge, using various extraction tests.For comparative objective, oven-dry sewage sludge without liming (unlimed sludge (S)) was also studied. The results of this study revealed that the percentages of the metals extracted from lime-stabilized sludge (pH = 12.05) and the amounts of the metals fractionated to the organically-bound fraction (30% H202 + 0.02 M HNO3 (pH2), 85 deg. C) in unlimed sludge were both in the order of Cu > Ph > Cr > Zn, meaning that the more the heavy metals (e.g., Cu) were fractionated to the organically-bound forms in unlimed sludge, the more unstable they were in the sludge after lime-stabilized. On the other hand, the metals (e.g., Zn) in lime-stabilized sludgewas more stable when they have less affinity for organics. Single extraction conducted at various pHs revealed that this effect was due to the irreversible dissolution of organics and some metals having a higher affinity for organics (e.g., Cu) at very high pH during processing and air drying of lime-stabilized sludge. Therefore, examining the fractionation of heavy metals in sewage sludge is useful for expecting heavy metal stability in the sewage sludges after lime-stabilized. [ABSTRACT FROM AUTHOR]

Four alkaline biosolids were produced from sewage sludge using lime,lime/sodium silicate, cement and cement/sodium silicate. X-ray diffractometry (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), single chemical extraction and sequential extraction were used to determine the characteristics of alkaline biosolids and untreated sewage sludge. The results of extraction tests revealed that the percentages of organically-bound metals in untreated sewage sludge were in the order of Cu>Pb>Cr>Zn. The percentages of exchangeable metals in four alkaline biosolids were also in this order, implying that the higher the affinity of heavy metals to organics in untreated sludge, the more unstable the heavy metals were in alkalinebiosolids. This effect was attributed to the irreversible dissolution of organically-bound metals at very high pH during processing and air drying of sludge. Sodium silicate addition promoted alkaline biosolids drying due to the formation of silica/silicate gels which held free water in sludges. The alkaline biosolids had relatively high CaCO3 equivalencies, ranging from 32.6 to 42.1% and may serve as potential liming amendments for acid soils. The CaCO3 peaks (29.46 deg. 2theta) in XRD graphs for alkaline biosolids indicate the occurrence of carbonation, especially for lime/sodium silicate-and cement/sodium silicate-treated biosolids. The porousness of lime/sodium silicate-treated biosolids as shown in the SEM micrograph corresponds to its smaller density (0.58 g/ml), compared to lime-treatedbiosolids. The micrograph of cement/sodium silicate-treated biosolids shows the absence of needle-like ettringite which commonly appears in Portland cement hydration. [ABSTRACT FROM AUTHOR]