Study On Treatment Of Wastewater Containing Low Concentrations Of NH₄⁺-N And RE³⁺ In Ion Rare Earth Mining Area By Biological Aerated Filter

For the ionic rare earth mines in southern China,the wet leaching process is mainly used to mine rare earths.A large amount of wastewater that containing ammonia-nitrogen?NH₄⁺-N?and rare earth ions(RE³⁺)are discharged into the mining area and surrounding water system from the mining process.The wastewater caused a series of serious environmental problems,so it is urgent to find a way to treat such wastewater effectively.In this paper,the biological aeration filter?BAF?that more advanced discontinuous way technology is used to treat low-concentration NH₄⁺-N and RE³⁺wastewater in ionic rare earth mining areas,and the soil of the rare-earth-mining-area is selected as the raw material to prepare BAF fillers.The preparation process of ceramsite filler was optimized by the crossover test,and explored and analyzed the removal effect,denitrification mechanism,and different operating parameters of BAF on the wastewater containing low concentrations of NH₄⁺-N and RE³⁺.The results show:?1?When the mining soil and pore-forming agent's ratio are 4:1,roasting temperature is1150?,holding time is an hour,the prepared ceramsite filler has better performance and reached the relevant national standard requirements of water treatment ceramsite;?2?The prepared ceramsite is used as BAF filler by using a composite film hanging method,and the film hanging is successful after about 22 days under the test conditions.Specifically,the conditions are:when the hydraulic residence time?HRT?are 4 hours,carbon to nitrogen ratio is 4,pH range 7.0 to 8.0,and the aeration rate is 1.8-3.6 L/min,the removal rate of NH₄⁺-N and TN in the ammonia nitrogen wastewater containing simulated rare earth mine area by BAF are 96.68%,74.59%,and NO₂^--N,NO₃^--N in effluent concentrations reached about 5.43 mg/L and 16.51 mg/L,respectively;?3?BAF has a good removal efficienct to RE³⁺,the removal rate is higher than 90%under the condition of 2 hours HRT with the 1.8-3.6 L/min aeration rate,made the concentration of RE³⁺in the effluent is less than 2 mg/L;?4?When using BAF treats wastewater that containing NH₄⁺-N and RE³⁺,RE³⁺will reduce the adsorption of filler to NH₄⁺-N,weaken the effect of aeration and blow off nitrogen removal and biological nitrification-denitrification of NH₄⁺-N,especially has the greatest impact on biological nitrification-denitrification of nitrogen removal.The removal capacity of BAF for NH₄⁺-N will to decline consistently when RE³⁺and NH₄⁺-N are simultaneously removed,while the removal rate of RE³⁺remain basically unchanged.The removal rate of NH₄⁺-N drops to about 56.77%,while the removal rate of RE³⁺is still maintained in 93.68%after 13 days stabilization treating.The BAF process can effectively treat the rare-earth-mining-area-wastewater that containing low concentration of NH₄⁺-N and RE³⁺,making the wastewater reach the standard of discharging.