Removing phosphorus from aqueous solutions by using iron-modified corn straw biochar

Iron-modified corn straw biocharwas used as an adsorbent to remove phosphorus from agricultural runoff. When agricultural runoffs with a total phosphorus (TP) concentration of 1.86 mg·L−1 to 2.47 mg·L−1 were filtered at a hydraulic retention timeof 2 h through a filtration column packed with the modified biochar, a TP removal efficiency of over 99% and an effluent TP concentration of less than 0.02 mg·L−1 were achieved. The isotherms of the phosphorus adsorption by the modified biocharfitted the Freundlich equationbetter than the Langmuir equation. The mechanism of the phosphorus adsorbed by the modified biocharwas analyzed by using various technologies, i.e. scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR). The results indicated that the surface of the modified biocharwas covered by small iron granules, which were identified as Fe3O4. The results also showed that new iron oxides were formed on the surface of the modified biocharafter the adsorption of phosphorus. Moreover, new bonds of Fe-O-P and P-C were found, which suggested that the new iron oxides tend to be Fe5(PO4)4(OH)3. Aside from removing phosphorus, adding the modified biocharinto soil also improved soil productivity. When the modified biochar-to-soil rate was 5%, the stem, root, and bean of broad beanplants demonstrated increased growth rates of 91%, 64%, and 165%, respectively.