Rare Earth Mine Wastewater Treatment Via Modified Constructed Rapid Infiltration System: Nitrogen Removal Performance And Microbial Community

The treatment of ion-type rare earth mine (REM) wastewater by a modified constructed rapid infiltration system (CRIS) was explored. Meanwhile, the activities of hydroxylamine oxidase, nitrite reductase and urease in the column were measured, and the microorganisms in the system were analyzed. When the hydraulic load was 0.1 m(3) m(-2).d(-1), the column height had a significant influence on the NH4+-N and TN removal rates. Specifically, the average NH4+-N and TN removal rates were 29.06 % and 14.83 %, respectively, for the CRIS with a 100 cm single-layer inorganic filler layer. While the average NH4+-N and TN removal rates increased to 69.70 % and 38.90 %, respectively, for the CRIS with a 140 cm double-layer inorganic filler layer. After increasing the hydraulic load from 0.1 m(3) m(-2).d(-1) to 0.2 m(3) m(-2).d(-1), the average NH4+-N and TN removal rates increased by 29.61 % and 15.84 %, respectively, in the long CRIS. The activities of hydroxylamine oxidase, nitrite reductase and urease in the column also improved. Nitrite reductase increased to 0.605 nitrite/min mg protein and hydroxylamine oxidase increased to 0.470 U/ mL g in the lower layer of the long CRIS. High-throughput sequencing analysis showed that the dominant bacterial phyla was mainly Proteobacteria and Planctomycetes. Pseudomonas, Bacillus and other aerobic denitrifying bacteria were detected at the genus level, as were the anaerobic denitrifying bacteria Comamonas and Thauera. These results illustrated that aerobic denitrification, anaerobic denitrification and anaerobic ammoxidation simultaneously existed during the CRIS treatment of REM wastewater to achieve TN removal. Furthermore, when using two full-scale CRIS in a series to treat actual REM wastewater, the NH4+-N removal rate reached 99.14 %. (C) 2021 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.