Appraisal of Bioavailability and Immobilization of Constituent Metals in Tannery Solid Waste Biochar in Soil Amendments Using Sunflower

Abstract

ABSTRACT The huge volume of tannery solid waste (TSW) can be reduced through conversion into tannery solid waste biochar (TSWB). Here, it was used as soil amendment at seven levels and the total metals and their soil bound or exchangeable fractions were determined through sequential extraction. The fate of metals was observed using sunflower as a test plant in a greenhouse trial using field soil amended with six concentrations (0.45–2.7%) of TSWB. The amendment rate of 1.8% proved to be the best for the growth of sunflower. Sequential extraction of metals indicated that 40% or more Cd, Cr and Pb remained in the exchangeable fraction, compared to less than 20% of Cu, Fe and Ni. Copper was mainly bound in the Fe-Mn and organic fractions, while Fe and Ni were mainly bound in the residual fraction. Copper, Fe and Ni were therefore immobilized in TSWB, while Cd, Cr, Pb, Mg and Zn were available as indicated by differential uptake in sunflower. All metals, except Cd, remained within the permissible limit in tissues of sunflower, while all were in permissible limits in the seeds. As a result, TSWB can be used as amendment below 1.8% to grow energy crops like sunflower.