[Effect of Biochar on the Adsorption Characteristics and Adsorption Mechanisms of Ammonia Nitrogen in Rainfall Runoff].

In order to study the performance and mechanisms of bioretention pond media ( biochar) for NH-N removal in rainfall runoff, three kinds of alkali modified biochars (marked as BC1, BC2, and BC3) were prepared with various concentrations of NaOH solution (1, 2, and 3 mol·L) to explore their adsorption performance for NH-N. The results showed that:① Appropriate modifications of the NaOH concentration increased the specific surface area and surface microstructure of biochar, with the content of O and the surface functional groups being enriched. In addition, BC2 possessed the best adsorption performance. ② The adsorption capacity reached a maximum when the pH was 9.0 and the dosage of biochar was 0.5 g·L. Compared with BC, the adsorption capacity of BC1 and BC2 increased by 6.4% and 10.8%, respectively, while BC3 decreased by 13.7%. Moreover, BC2 had an optimal adsorption efficiency with a saturated adsorption capacity of 16.76mg·g. ③ The adsorption mechanism of biochar belonged to chemical adsorption with a monomolecular layer. The adsorption process was promoted by the high pH of biochar, the electrostatic attraction of biochar pores, the complexation and oxidization of the functional groups of hydroxyl (-OH), carboxyl (-COOH), and carbon-oxygen single bond (C-O). To sum up, the proper amount of NaOH to modify biochar can improve the adsorption performance of NH-N, and the modified biochar can be used as media of the bioretention pond to remove NH-N.