Nitrogen removal performance and microbial community analysis of immobilized biological fillers in rare earth mine wastewater

The present study sought to treat the ion-adsorption type rare earth mine wastewater in a pilot plant system using the nitritation-denitrification process with immobilized biological fillers. Meanwhile, the microbial community structure in the immobilized fillers was analyzed. The ammonia nitrogen removal rate of the nitritation fillers reached 0.43 kg N m(-3) d(-1) on day 61 (28.1 degrees C) and the total nitrogen removal rate of the denitrification fillers reached 0.51 kg N m(-3) d(-1) on day 58 (27.8 degrees C) under the hydraulic retention time of 3.4 hr and a fillers volume ratio of 8% (v/v). The average NH4+-N and TN removal efficiencies of the nitritation-denitrification process were 96.9% and 96.8%, respectively, during the steady state operation period (day 26-72). The results also indicate that high DO (5.5-6.5 mg L-1) could induce rapid growth of nitrite-oxidizing bacteria (NOB) in the nitritation fillers, even though the initial NOB proportion is extremely low. The optimal operational performance of the denitrification fillers reactor was the COD/(NO2--N + NO3--N) ratio of 3.7-4.2. The high-throughput sequencing analysis showed that the functional bacteria in the immobilized fillers could maintain a competitive advantage. The abundance of Nitrosomonas in the nitritation fillers increased from 6.58% to 21.24%, while Thauera and Ottowia were the dominant denitrifying bacteria genera in the denitrification fillers.

Automated summary

This study investigated the treatment of ion-adsorption type rare earth mine wastewater using the nitritation-denitrification process with immobilized biological fillers. The results showed high efficiency in ammonia nitrogen and total nitrogen removal during steady state operation. Additionally, high dissolved oxygen levels could induce rapid growth of nitrite-oxidizing bacteria, with functional bacteria maintaining a competitive advantage in the immobilized fillers.