Experimental Study On The Treatment Of Ammonia Nitrogen Wastewater From Rare Earth Mines By Partial Denitrification-Partial Nitrification-Anammox Coupling

The mining of ionic rare earth ore requires a large amount of ammonium sulfate solution for leaching and desorption extraction.For a long time after mining,the ammonium remaining in the tailings or ore soil is continuously leached out,forming ammonia nitrogen tailwater from rare earth mines and flowing into the surface runoff.The problem of ammonia nitrogen pollution in the water environment of the basin is prominent.The ammonia nitrogen tailwater of ionic rare earth mines is inorganic ammonia nitrogen wastewater,and its water quality characteristics determine that the widely used nitrification/denitrification wastewater denitrification technology requires aeration and a large amount of organic carbon sources,so the treatment cost is high.In this paper,based on the research results of the laboratory test,aiming at the water quality characteristics of the ammonia nitrogen tailwater of the ionic rare earth mine,a set of 50 m³/d"Partial Denitrification-Partial Nitrifition-Anammox coupling process（PD-PN-Anammox）"pilot plant was built in the mine wastewater treatment station.Taking the denitrification of ammonia nitrogen wastewater from ionic rare earth mines as the research goal,the start-up,operation regulation and performance research of PD,PN and Anammox reactors were carried out respectively,and the denitrification performance of PD-PN-Anammox coupled operation was investigated in depth.The main conclusions of this study are as follows:（1）Using COD/NO₃^-as the control variable,nitrite nitrogen and nitrate nitrogen in the effluent of the reactor as feedback indicators,the control strategy of progressively lowering COD/NO₃^-（4.0→2.1）can successfully start the pilot-scale PD reactors within 30 days scale PD reactor.On the 27th day,the nitrate removal rate（NRR）and nitrite accumulation rate（NAR）reached 89%and 38%,respectively.The operation test shows that the combined control strategy of maintaining low COD/NO₃^-（2.0）and adding chemicals after stirring the water,the PD process has a strong ability to resist the impact of water quality fluctuations,and achieves a stable improvement in efficiency（NAR=58%±7.32%）.Sludge morphology analysis showed that microbes secreted a large amount of extracellular polymer（EPS）and combined with Ca2+,which was the main reason for the sludge to maintain good retention capacity.（2）Using the combined control strategy of p H-DO control and intermittent aeration（aeration for 30 minutes and aeration for 30 minutes）,the pilot-scale PN reactor can be quickly started within 13 days,and the ammonia nitrogen removal rate（ANR）and NAR of long-term operation were stable at 94.18%±10.47%and85.05%±9.41%,respectively.In the face of the impact of the influent ammonia nitrogen fluctuation,fine-tuning the aeration time in the aeration stop time（25 min:35min）was more conducive to maintain the PN reactor effluent NH₄⁺:NO₂^-at 1:1.2.Sludge morphology analysis showed that the EPS secretion of sludge microorganisms in the pilot-scale PN reactor was higher than that in the laboratory simulated wastewater reactor.（3）Using the operation strategy of intermittent water inflow in the initial stage of startup and continuous water inflow in the later stage,after 105 days of successful startup of the pilot-scale perforated plate Anammox reactor,the anammox bacteria Candidatus Kuenenia obtained high-efficiency enrichment（increased from 0%to16.67%）.The analysis of the anammox sludge morphology showed that compared with the anammox sludge morphology of the laboratory reactor,the sludge morphology in the pilot-scale reactor had obvious void structure,this may be the reason why the wastewater contains rare earth elements.（4）The test shows that the pilot-scale PD-PN-Anammox coupling process can run stably for a long time,the total nitrogen removal rate（TNR）of the system reaches81.20%±7.95%,and the effluent can stably meet the"Emission Standard of Rare Earth Industry Pollutants"（NH₄⁺≤15mg/L,TN≤30mg/L）.With the increase of running time,the key functional bacteria Candidatus Kuenenia increased from 16.67%to 48.28%.After the PD-PN-Anammox coupling process ran for 116 days,EPS reduction and functional bacteria exposure appeared on the sludge surface in the PN reactor and Anammox reactor.