Adsorption of phosphate by Mg/Fe-doped wheat straw biochars optimized using response surface methodology: Mechanisms and application in domestic sewage

Abstract

In this study, Mg/Fe-doped biochar (MFDB) was prepared using the impregnation pyrolysis method, and its preparation was optimized using response surface methodology (RSM). The competitive adsorption between dissolved organic matter (DOM) and phosphorus was also investigated. The best adsorption capacity was obtained with an Mg impregnation ratio of 3.17:1 (Mg: biomass, g:g), Fe impregnation ratio of 1.3:1 (Fe: biomass, g:g), and pyrolysis temperature of 491°C. The adsorption capacity of MFDB for phosphorus was 179.21 mg/g at 40°C, an initial phosphate concentration of 50 mg/g and pH 4. The phosphate adsorption by MFDB conformed to a pseudo-primary and secondary adsorption kinetic model, proving the coexistence of physical and chemical adsorption. The adsorption mechanisms, including ligand exchange, electrostatic interaction, and complexation reaction were revealed. As the pH increased, it weakened the electrostatic interaction of phosphate by MFDB and the ligand exchange between phosphate and OH<sup>-</sup>. When the pH was less than 3, the metal oxide dissolved. For pH values exceeding, OH<sup>-</sup> competed with phosphate for adsorptio, which also weakened the complexation of phosphate and MFDB. The DOM in domestic wastewater had a slight effect on the phosphorus adsorption. The phosphorus removal rates were closely related to lignin-like humic acid and tryptophan.

Short-Term Effect of Biochar on Soil Organic Carbon Improvement and Nitrous Oxide Emission Reduction According to Different Soil Characteristics in Agricultural Land: A Laboratory Experiment

“…As a result, there are fertile soils and poor soils even on agricultural land. However, research so far has focused on the development of biochar feedstocks to reduce greenhouse gases [28,[38][39][40], the effect of increasing crop growth and yield [41][42][43], the effects of biochar according to climate zone [13,44], and adsorption of water and soil pollutants [45,46]. Although there have been studies evaluating the effect of biochar on existing fertile farmland [13,14,38,42,47], studies on the effect of biochar on poor soil that can be converted to cropland have been limited.…”