Enhancement stabilization of heavy metals (Zn, Pb, Cr and Cu) during vermifiltration of liquid-state sludge

• Published in: Bioresource technology Vol. 146; pp. 649 - 655
• Main Authors: Yang, Jian, Zhao, Chunhui, Xing, Meiyan, Lin, Yanan
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.10.2013; Elsevier
• Subjects: Animals; Applied sciences; Biodegradation, Environmental; Biological and medical sciences; Biological Assay; Biological Oxygen Demand Analysis; Chromium; Chromium - chemistry; Copper - chemistry; Earthworm; Equipment Design; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; Heavy metal; Heavy metals; Hydrogen-Ion Concentration; Lead - chemistry; Metals, Heavy - chemistry; Oligochaeta - metabolism; Oxygen demand; Phosphorus - chemistry; Pollution; Risk; Risk analysis; Sewage; Sewage sludge; Sludge; Soil Pollutants - analysis; Soil Pollutants - chemistry; Speciation; Stabilization; Vermifiltration; Wastes; Zinc; Zinc - chemistry; Earthworm; Stabilization; Sewage sludge; Vermifiltration; Heavy metal; Liquid state; Fauna; Annelida; Oligochaeta; Zinc; Macrofauna; Lead; Wastes; Invertebrata
• ISSN: 0960-8524; 1873-2976
• DOI: 10.1016/j.biortech.2013.07.144

•Stabilization of heavy metals in sludge treated by vermifilter has not been reported.•Variation of heavy metal concentrations was mainly due to organics degradation.•Heavy metals were transformed into stable fractions after vermifilter treatment.•Heavy metal accumulation by earthworms mainly depended on their chemical speciation.•Vermifiltration technology relieved the potential risk of heavy metals in sludge. This paper illustrated the potential effect of earthworms on heavy metal stabilization after vermifiltration of liquid-state sludge. Significant enhancement of organics degradation in sludge caused an increase of heavy metal concentrations in VF effluent sludge. However, the analysis of heavy metal chemical speciation indicated earthworms made unstable fractions of heavy metals transformed into stable fractions. Further investigation using principal component analysis revealed that transformations of heavy metal fractions were mainly due to the changes in sludge physico-chemical properties of pH, soluble chemical oxygen demand and available phosphorus. The bioassay of earthworms indicated that only zinc was accumulated by earthworms because the unstable fraction was its main chemical speciation. Furthermore, risk analysis demonstrated that earthworm activities weakened heavy metal risk due to the formation of stable fractions although their total concentrations increased. These results indicated that earthworms in vermifilter had a positive role in stabilizing heavy metals in sewage sludge.