Quantitative evaluation on phosphate adsorption by modified biochar: A meta-analysis

A great deal of research has indicated that modified biochar has better phosphate adsorption ability compared with unmodified biochar, but some results are contradictory, and a quantitative summary of these studies is still missing, implying high uncertainties of the application of the modified biochar. In this study, the phosphate adsorption ability of modified biochar and the closely related environmental parameters were quantitatively evaluated by meta-analysis. Results indicate that, compared with the unmodified biochar, the phosphate adsorption capacity and removal rate of the modified biochar increased by 451 % and 312 %, respectively; the adsorption isotherm constant-Ⅰ (IC-Ⅰ), adsorption isotherm constant-Ⅱ (IC-Ⅱ) and thermodynamic constants significantly increased by 322 %, 163 % and 163 %, respectively. The phosphate adsorption capacity of biochar pre-modified and post-modified significantly increased by 371 % and 514 %, respectively. The effects of modification on adsorption rate, rate constant, IC-Ⅰ, IC-Ⅱ and thermodynamic constant were significantly different. The effect of physical modification on the phosphate adsorption capacity of was not significantly. In the chemical modification method, the metal modification shows the highest performance on phosphate adsorption in regardless of adsorption capacity, adsorption rate, isotherm constant and thermodynamic constant. Compared with the biochar from other raw materials, the modified manure biochar (preparation and modification of biochar using animal manure as raw material) showed the largest capacity of phosphate adsorption, with a significant raising of 780 %. The effect size of modified biochar on phosphorate adsorption was correlated with the pyrolysis temperature during biochar production. The modified biochar that was prepared at a higher pyrolysis temperature (>700 °C) with higher mineral content is more helpful in improving the phosphate adsorption capacity. This meta-analysis demonstrates that modified biochar generally enhances the aqueous phosphate adsorption when applied to water by using one modification method or in combination with several methods. These findings provide a scientific basis for developing more reasonable eutrophication control strategies toward widespread adoption of biochar as biomaterials for phosphorus removal from the water ecosystem.