Better waste utilization: Mg-modified biochar from wetland plant waste for phosphorus removal and carbon sequestration

Abstract

Withered wetland plants have become a treat to water ecological security. To address the issue of waste biomass disposal, a typical wetland plant, Hydrocotyle vulgaris, was utilized to produce Mg-modified biochar (MBC) for efficient phosphorus (P) removal and stable carbon sequestration. The adsorption behavior fit Langmuir isotherm and the pseudo second-order kinetic models, which revealed the nature of monolayer chemical adsorption of MBC. The removal of P was achieved through physical diffusion, Mg²⁺ precipitates, surface complexation and electrostatic attraction. Based on the analysis of thermodynamics models, it can be concluded that the adsorption behavior of P by MBC was spontaneous and endothermic. The MBC exhibited a maximum phosphorus adsorption capacity of 314.048 mg/g. Concurrently, the specific surface area was enhanced from 529.974 m²/g to 931.019 m²/g. The research has also recorded valuable data about the carbon sequestration potential of MBC with the carbon content reaching 0.51 g per g of biochar. It was found from the outcomes that Mg-modified biochar had outstanding carbon sequestration potential and significantly improved P removal efficiency.