The fate of Cu, Zn, Pb and Cd during the pyrolysis of sewage sludge at different temperatures

Abstract

In the present study, a sequential extraction procedure, recommended by the Community Bureau of Reference (BCR), was used for the fractionation of the heavy metals Cu, Zn, Pb and Cd in sewage sludge and its residues produced after pyrolysis at different temperatures from 250 to 700 degrees C. The results show that, in the sludge sample, the sum of the percentages of the reducible and oxidizable fractions for all metals except Cu was very high (65.4% for Cd, 85.7% for Pb, 78.7% for Zn), whereas the sum of the percentages of the oxidizable and residual fractions for Cu was very high (88.8%). The same result could be attained in the residues. Statistical analysis shows that at low temperatures the variation in pyrolysis temperature did not effectively contribute to the distribution of metal speciation in the residues. Meanwhile a modified Toxicity Characteristic Leaching Procedure (TCLP) was employed to determine the leachability of these four metals. The result indicates that the TCLP concentration of Cu, Zn, Pb and Cd dropped sharply after the temperature reached 350 degrees C, 550 degrees C, 500 degrees C and 400 degrees C respectively, which means pyrolysis can enhance the stability of these four metals when the temperature is high enough.

Potential impacts of using sewage sludge biochar on the growth of plant forest seedlings

“…However, its application to soil may sometimes be risky because of the potential presence of pathogenic organisms and heavy metals (HE et al, 2010). Thermal treatment of sewage sludge through pyrolysis produces biochar, reducing volume and organic contaminant characteristics (LIU et al, 2014) Silva et al…”

Impact of thermal treatment of mixtures of sewage sludge and plant material on selected chemical properties and Vibrio fischeri response

“…Based on the obtained own results, the thermal treatment process favored the increase in contents of forms of some of the studied trace elements extracted with water. It resulted from a loss of unstable aliphatic bonds and formation of more stable aromatic bonds [39,40]. According to Hossain et al [11], despite an increase in the total content of trace elements as a result of pyrolysis of sewage sludge, the content of bioavailable forms did not change significantly.…”

The Effect of Low-Temperature Conversion of Plant Materials on the Chemical Composition and Ecotoxicity of Biochars

“…Based on our study results, we found that the process of thermal conversion of organic materials did not cause mobilisation of available forms of most of the studied trace elements. Research results published by He et al [40] indicate that thermal conversion of organic materials results in a greater stability of such trace elements as Cd, Pb, Zn, and Cu.…”

“…In the studies conducted by Yachigo and Sato [39], higher pyrolysis temperature resulted in a considerable increase in the zinc and copper contents in the resulting material, but it did not change the cadmium content. In the view of He et al [40], the pyrolysis temperature exceeding 350°C results in a greater stability of such trace element as Cd, Pb, Zn and Cu. This phenomenon occurs due to the loss of unstable aliphatic connections and creation of more stable aromatic connections [41].…”