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. 2021 Jan 18;14(2):447.
doi: 10.3390/ma14020447.

Experimental Investigation into the Effect of Pyrolysis on Chemical Forms of Heavy Metals in Sewage Sludge Biochar (SSB), with Brief Ecological Risk Assessment

Binbin Li  1 , Songxiong Ding  2 , Haihong Fan  1 , Yu Ren  1
Affiliations

Experimental Investigation into the Effect of Pyrolysis on Chemical Forms of Heavy Metals in Sewage Sludge Biochar (SSB), with Brief Ecological Risk Assessment

Binbin Li et al. Materials (Basel). .

Abstract

Experimental investigations were carried out to study the effect of pyrolysis temperature on the characteristics, structure and total heavy metal contents of sewage sludge biochar (SSB). The changes in chemical forms of the heavy metals (Zn, Cu, Cr, Ni, Pb and Cd) caused by pyrolysis were analyzed, and the potential ecological risk of heavy metals in biochar (SSB) was evaluated. The conversion of sewage sludge into biochar by pyrolysis reduced the H/C and O/C ratios considerably, resulting in stronger carbonization and a higher degree of aromatic condensation in biochar. Measurement results showed that the pH and specific surface area of biochar increased as the pyrolysis temperature increased. It was found that elements Zn, Cu, Cr and Ni were enriched and confined in biochar SSB with increasing pyrolysis temperature from 300-700 °C; however, the residual rates of Pb and Cd in biochar SSB decreased significantly when the temperature was increased from 600 °C to 700 °C. Measurement with the BCR sequential extraction method revealed that the pyrolysis of sewage sludge at a suitable temperature transferred its bioavailable/degradable heavy metals into a more stable oxidizable/residual form in biochar SSB. Toxicity of heavy metals in biochar SSB could be reduced about four times if sewage sludge was pyrolyzed at a proper temperature; heavy metals confined in sludge SSB pyrolyzed at about 600 °C could be assessed as being low in ecological toxicity.

Keywords: BCR sequential extraction; ecological risk assessment; heavy metals; pyrolysis; sewage sludge.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Diagram of self-made pyrolysis device. 1: Nitrogen, 2: Rotor flow, 3: Tube furnace, 4: Heating tube, 5: Sand bath, 6: Particle sampler, 7: Quartz filter, 8: Wash gas bottles.
Figure 2
Figure 2
FTIR spectrum of the SS and its biochars. SS, sewage sludge; SSB-X, biochar prepared by pyrolysis of sewage sludge at X temperature (°C).
Figure 3
Figure 3
SEM images of sewage sludge and its biochar SSB. (a) SS(10,000×), (b) SS(20,000×), (c) SSB-300(10,000×), (d) SSB-300(20,000×), (e) SSB-400(10,000×), (f) SSB-400(20,000×) (g) SSB-500(10,000×), (h) SSB-500(20,000×), (i) SSB-600(10,000×), (j): SSB-600(20,000×), (k) SSB-700(10,000×), (l) SSB-700(20,000×).
Figure 4
Figure 4
Residual rate of heavy metals in biochar at different pyrolysis temperatures.
Figure 5
Figure 5
Chemical forms of heavy metals in SS and biochar.
Figure 6
Figure 6
Cf, Er, RI of SS and biochar. (a) Decrease of metals contamination/pollution factor with increase of pyrolysis temperatures (b) Decrease of metals ecological risk as pyrolyzed at rising temperature (c) Overall ecological risk index of various pyrolyzed biochar SSB.
See this image and copyright information in PMC

References

    1. Yang G., Hu Y., Wang J. Biohydrogen production from co-fermentation of fallen leaves and sewage sludge. Bioresour. Technol. 2019;285:121342. doi: 10.1016/j.biortech.2019.121342. - DOI - PubMed
    1. Fan H., Lv M., Wang X. Effect of Cr on the Mineral Structure and Composition of Cement Clinker and Its Solidification Behavior. Materials. 2020;13:1529. doi: 10.3390/ma13071529. - DOI - PMC - PubMed
    1. Xia Y., Tang Y., Shih K. Enhanced phosphorus availability and heavy metal removal by chlorination during sewage sludge pyrolysis. J. Hazard. Mater. 2020;382:121110. doi: 10.1016/j.jhazmat.2019.121110. - DOI - PubMed
    1. Thomsen T.P., Sarossy Z., Ahrenfeldt J., Henriksen U.B., Frandsen F.J., Muller-Stover D.S. Changes imposed by pyrolysis, thermal gasification and incineration on composition and phosphorus fertilizer quality of municipal sewage sludge. J. Environ. Manag. 2017;198:308–318. doi: 10.1016/j.jenvman.2017.04.072. - DOI - PubMed
    1. Jin J., Li Y., Zhang J., Wu S., Cao Y., Liang P., Zhang J., Wong M.H., Wang M., Shan S., et al. Influence of pyrolysis temperature on properties and environmental safety of heavy metals in biochars derived from municipal sewage sludge. J. Hazard. Mater. 2016;320:417–426. doi: 10.1016/j.jhazmat.2016.08.050. - DOI - PubMed

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