Sodium lignosulfonate enhances the insoluble sulfates and phosphates formation of heavy metal passivation in municipal sludge aerobic composting

Abstract

Municipal sludge aerobic compost application in land faces limitations due to the potential hazard of heavy metals, and adding heavy metal passivator proved a pathway to relieve this issue. However, as a heavy metal passivator, sodium lignosulfonate hasn't been applied in municipal sludge aerobic compost. In this paper, we selected sodium lignosulfonate and proportionally added it to municipal sludge aerobic compost for 45 days to evaluate the passivation impact of Cr, Zn, Pb and Cu. The results showed that sodium lignosulfonate can improve the stability of heavy metals by reducing the bioavailable forms. Specifically, adding 5% sodium lignosulfonate showed the best passivation effect of heavy metals with passivation rates of Cr, Zn, Pb and Cu at 81.46%, 32.58%, 98.61% and 30.91%, respectively. What’s more, scanning electron microscope energy dispersive system, Fourier transforms infrared spectroscopy, X-ray photoelectron spectroscopy and X-ray powder diffraction revealed that sodium lignosulfonate promoted the passivation of heavy metals by enhancing the degradation of organic matter and forming new insoluble sulfates and phosphates. This study might contribute to the understanding of the mechanism of heavy metal passivation during aerobic composting.

Graphical abstract