Ammonium removal efficiency of biochar-based heterotrophic nitrifying bacteria immobilization body in water solution

Abstract

In order to explore the performance of biochar-based microbial immobilization body in ammonium removal from water and potential mechanisms, a strain of heterotrophic nitrifying bacteria (HNB) was isolated from activated sludge, and the biochemical and molecular biological identification of HNB was carried out. Moreover, HNO<sub>3</sub>-, Mg<sup>2+</sup>-, NaOH<sub>-</sub>, and NaOH+Mg<sup>2+</sup>-modified rice husk-derived biochars were prepared. Then all the five kinds of biochars, including the original biochar, were used as carriers of HNB to remove NH<sub>4</sub><sup>+</sup><sub>-</sub>N from water. Results showed that HNB was classified as <i>Pseudomonas</i>, and the 72-h NH<sub>4</sub><sup>+</sup><sub>-</sub>N removal ratio of the free bacteria reached 80.24%. Compared with biochar itself, biochar-based HNB immobilization body showed a much stronger ability to remove NH<sub>4</sub><sup>+</sup><sub>-</sub>N, especially for NaOH<sub>-</sub> and NaOH+Mg<sup>2+</sup>-modified biochars. At the initial NH<sub>4</sub><sup>+</sup><sub>-</sub>N concentration of 100 mg/L and biochar addition dose of 10 g/L, NH<sub>4</sub><sup>+</sup><sub>-</sub>N removal ratio of NaOH<sub>-</sub> and NaOH+Mg<sup>2+</sup>-modified biochar-based HNB immobilization bodies reached 57.78% and 58.35% after 5 h, and reached 88.66% and 90.93% after 48 h respectively, which were obviously higher than the original, HNO<sub>3-</sub> and Mg<sup>2+</sup>-modified biochar-based HNB immobilization bodies. The phenomenon resulted from significantly higher bacteria adsorption ability of NaOH<sub>-</sub> and NaOH+Mg<sup>2+</sup>-modified biochars, which reached 773.75 and 941.17 nmol P/g biochar, respectively.