Recovery of nutrients from wastewater by a MgCl2 modified zeolite and their reuse as an amendment for Cu and Pb immobilization in soil

Abstract

In this study, nutrients in wastewater were simultaneously removed by magnesium modified zeolite, and the precipitates of the nutrient recovery process were applied as a kind of amendment to achieve copper and lead immobilization in contaminated soil. Mg²⁺ released from MgCl₂ modified zeolite (Zeo-Mg) in the nutrient recovery process was considered as the magnesium source for struvite crystallization. The optimal efficiencies of nutrient recovery using Zeo-Mg were obtained at pH 9. When the dosage and reaction time were separately controlled at 10 g L⁻¹ and 180 min, the ammonia nitrogen (AN) and phosphate removal efficiencies reached 61.22% and 94.73%, respectively. The high simultaneous nutrient removal efficiencies were attributed to cooperation of Zeo-Mg adsorption and struvite formation. The recovery precipitates, zeolite and MAP (Zeo/MAP), were evidenced as a suitable amendment for both Cu and lead immobilization in soil. At a dosage of 5 g amendment per 50 g soil, the available concentrations of Cu and Pb separately reduced to 278.88 mg kg⁻¹ and 168.36 mg kg⁻¹ under 21 day treatment. On further increase in immobilization time, the available concentrations of Cu and Pb reached a relatively steady state. The acid soluble species of Cu and Pb transformed to more inert reducible and residual species and showed that Cu and Pb were successfully immobilized by Zeo/MAP. According to the experiments and characterization results, zeolite adsorption and phosphate formation were the major immobilization mechanisms of Cu and Pb in contaminated soil.