Leaching Characteristics of Heavy Metals and Plant Nutrients in the Sewage Sludge Immobilized by Composite Phosphorus-Bearing Materials

Abstract

In order to evaluate the environmental risk caused by land application of sewage sludge, leaching characteristics of heavy metals and plant nutrients in the sewage sludge immobilized by composite phosphorus-bearing materials were investigated. Their cumulative release characteristics were confirmed. Furthermore, the first-order kinetics equation, modified Elovich equation, double-constant equation, and parabolic equation were used to explore dynamic models of release. Results showed that sewage sludge addition significantly increased electricity conductivity (EC) in leachates, and the concentrations of heavy metals (Cu, Cr, Zn) and plant nutrients (N, P, K) were also obviously increased. The highest concentrations of Cu, Cr, and Zn in the leachates were all below the limit values of the fourth level in the Chinese national standard for groundwater quality (GB/T14848-2017). The immobilization of composite phosphorus-bearing materials reduced the release of Cu and Cr, while increased that of Zn. The fitting results of modified Elovich model and double-constant model were in good agreement with the leaching process of heavy metals and plant nutrients, indicating their release process in soil under simulated leaching conditions was not a simple first-order reaction, but a complex heterogeneous diffusion process controlled by multifactor.

Effect of cleanup of spiked sludge on corn growth biosorption and leaching of metals

“…McBride [38] may serve as a further argument to explain the differences reported above, when comparing our results to those of Li et al [49], notably with regards to the concentration of metals in water leaching from biosolid amended soils.…”

“…Total inputs of metals were lower (in case of Cu and Cr) or relatively close (in case of Zn) to our tested loads. Although, the levels of all three metals, Cu, Cr and Zn, in leachates reported by Li et al [49] attained concentrations as high as (in µg L -1 ) 1 340, 70 and 1 060, respectively. However, one has to take into account that both experiments are quite different each from other.…”

“…In comparison, Gray et al [48] measured the concentration of Cd in leachate from New Zealand pasture soils that were treated repetitively with phosphate fertilizer, and found higher results: 0.35-1.57 g Cd L -1 . Li et al [49] tested mixtures of soil with unstabilized or stabilized sludge (using phosphorus based products), and measured metals (Cu, Cr and Zn) leaching in the outlet water. Total inputs of metals were lower (in case of Cu and Cr) or relatively close (in case of Zn) to our tested loads.…”

“…However, one has to take into account that both experiments are quite different each from other. Li et al [49] did not consider any plant uptake, but only leaching of metals from cylinders filled with biosolid-soil mixtures, that were irrigated with distilled water.…”

Migration and Transformation of Heavy Metals in the Soil of the Water-Level Fluctuation Zone in the Three Gorges Reservoir under Simulated Nitrogen Deposition

“…e first-order kinetic equation, double-constant rate equation, parabolic equation, and modified Elovich equation are the common mathematical models to describe the characteristics of dynamics of soil HMs [20,21]. e first-order kinetic equation is good at describing the simpler surface process of the diffusion mechanism [22].…”