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An investigation into the mobility of heavy metals in soils amended with biosolids-derived biochar

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  2021 ASABE Annual International Virtual Meeting  2100103.(doi:10.13031/aim.202100103)
Authors:   Serhiy Marchuk, Diogenes L. Antille, Payel Sinha, Seija Tuomi, Peter W. Harris, Bernadette K. McCabe
Keywords:   Copper, Chromium, Land application of biosolids, Leaching, Potentially toxic elements, Sewage Sludge, Zinc.

Abstract. A laboratory experiment that was conducted to gain an understanding of heavy metals dynamics in soils amended with biosolids (treated sewage sludge) and biochar produced from biosolids. The findings of this study, albeit limited in scope, go some way to inform the development of a scientific-based framework that supports practical and cost-effective management of biochar intended for land application. The risk of heavy metals (Zn, Cu, Cr) leaching in two soils of contrasting mineralogy and physico-chemical properties (Yellow Chromosol and Red Ferrosol) was quantified in a laboratory setup using leaching columns. Application of biosolids and biochar to soil increased pH of the leachate solution, and it increased with the rate of biosolids or biochar applied to soil. Differences in pH of leachate between biosolids and biochar-treated soil were not significant. Zinc (Zn) recovered in leachate was higher in the Red Ferrosol than the Yellow Chromosol, but total Zn recovered after six leaching events was less than 20 mg kg-1 , and there was no clear effect of rate. There was a little more Zn recovered in leachate from biochar- compared with biosolids-treated soil. Copper (Cu) recovered in leachate was higher in the Red Ferrosol than the Yellow Chromosol, but no Cu was recovered after the fourth leaching event, and in both soils Cu in leachate increased with the application rate. The amount of Cu recovered in leachate from biochar-treated soil was about one-third the amount recovered from biosolids-treated soil. Chromium (Cr) recovered in leachate was similar in both soils and recoveries were fairly consistent between-leaching events. In both soils, Cr recovered in leachate increased with the application rate. Total Cr recovered in leachate from biochar-treated soil was about eight times lower than from biosolids-treated soil. There is a need to extend the work reported here and to consider other soil types (e.g., Vertisols) that may respond differently from the physico-chemical and hydrological perspectives, and to capture the dynamics of other heavy metals as well as phosphorus, which were not part of this study. Based on the results of this work, there appears to be potential for future use of biochar in these two Queensland soils.

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