Phytoextraction of heavy metals from tannery sludge: A cleaner approach

Worldwide, tannery sludge management has become a big challenge due to containing heavy metals, especially chromium. In this study, phytoextraction of heavy metals from tannery sludge by Napier grass (Pennisetum purpureum) is presented. Heavy metals-chromium (Cr), copper (Cu), zinc (Zn), and lead (Pb) in tannery sludge were found at 12686, 371, 265, and 66 mg/kg, respectively. Separately, Napier grass was harvested on raw tannery sludge and garden soil and examined for 16 and 20 weeks after the sowing of seeds. Metal extraction from tannery sludge in Napier grass was found in a series of Cr > Zn > Cu > Pb; the most accumulation was reported in shoot parts of plants in the order of shoots > roots > leaves. Accumulation of Cr in Napier grass at 16 and 20 weeks was 37% and 66%, respectively. An increasing trend of heavy metal gathering in the plant was found significantly by extending the harvesting period from 16 to 20 weeks. Translocation of Cr and Pb was greater than unity (1.623 and 1.339) indicating the suitability of phytoextraction. Further, Napier grass is a rapid-yielding tropical grass, which showed a high degree of growth tolerance that could be used for treating heavy metals contaminated tannery sludge.

Automated summary

This study presents a method of phytoextraction of heavy metals from tannery sludge using Napier grass. Napier grass showed higher accumulation of chromium and an increasing trend of heavy metal gathering by extending the harvesting period. Moreover, Napier grass is a fast-growing tropical grass with high growth tolerance, making it suitable for treating heavy metal-contaminated tannery sludge.