Search

Heavy metals were removed from industrial sludge by traditional and microwave-assisted acid extraction approaches. The effects of acid concentration, extraction time, sludge particle size and solid/liquid (S/L) ratio on copper-extraction efficiency were assessed. Leaching with increased acid concentrations increased the yield of heavy metals from the industrial sludge. In microwaveassisted acid extraction, reducing the S/L ratio and sludge particle size increased copperextraction efficiency. These experimental findings indicate that S/L ratio most strongly influenced microwave-assisted acid extraction. Both traditional and microwave-assisted acid extraction demonstrate that sulfuric acid was an effective extractant, and the copper fraction in extracted sludge shifted from being primarily bound to Fe-Mn oxides and organic-matter partition, to being mostly bound to organic matter, remaining as a residue during acid extraction. [ABSTRACT FROM AUTHOR]

Swine manure was comprehensively characterized with respect to Cu and Zn due to feed additives. Separated swine manure (SSM) composts were collected from five pig farms at Tainan County. The total content, base extractability, synthetic acid rainwater (SAR) solubility, and leachability at varying pH of Cu and Zn were determined to assess its environmental hazard. The influence of dissolved organic carbon (DOC) from compost on leaching of these elements was evaluated. The SSM composts were enriched with Cu (208-1380 mg/kg) and Zn (847-2840 mg/kg). The SAR and neutral pH leachable fractions of Cu, Zn, and organic C were generally low (< 6% of their total content). Copper leachability in F2 compost, however, was high (14%), resulting from immaturity and associated substantial dissolution of organic C (11%). Most of Cu (86% on average) while small portion of Zn (14% on average) were distributed on humic substances (HS) which comprised about 40% of total compost organic C. Extracted Cu increased rapidly and was highly correlated to the increase of organic C concentration as the pH raised above pH 8, while extracted Zn remained low. High leachability of Cu at alkaline pH and during HS extraction was due at least in part to complexation with DOC. [ABSTRACT FROM AUTHOR]

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]