The Effect And Mechanism Of Rare Earth Elements (Lanthanum(?)) On Partial Nitrification And Anammox Process

A large amount of ammonium sulfate is used as a leaching agent in the extraction process of ionic rare earths,which leads to the production of mine ammonia nitrogen wastewater containing rare earth elements in the abandoned rare earth mine tailings.At present,the nitrification/denitrification process widely used in rare earth mine wastewater treatment faces the problems of insufficient denitrification efficiency and high operating cost.Therefore,it is very urgent to develop a new type of high-efficiency energy-saving biological denitrification process.The partial nitrification/Anammox process is considered to be the most promising biological denitrification process.Considering the potential effects of rare earth elements in this wastewater on the biological nitrogen conversion process,this study focuses on the effects and mechanisms of rare earth elements on partial nitrification and Anammox process.The main conclusions of this study are as follows:(1)A new pH-DO control strategy has been developed.Using this strategy,the partial nitrification process was quickly started within 15 days,and the nitrite accumulation rate(NAR)and ammonia nitrogen removal rate(ANR)in the long-term operation phase(58 days)reached 97.33±0.5%and 97.76±1.1%,respectively.Then,the NAR and ANR remained basically unchanged after reducing the influent ammonia,indicating that the process under this strategy can resist the impact of fluctuating water quality.The analysis of bacterial competition kinetics confirmed the efficient enrichment of functional bacteria(AOB)and the selective elimination of competitive bacteria by this strategy.(2)The effect and mechanism of rare earth elements(Lanthanum(?))on the partial nitrification process was determined by using batch experiments.Lanthanum(?)(La(?))significantly increased the ammonia oxidation rate(AOR)at low doses(?20 mg/L),but reduced AOR at high doses(?20 mg/L).Inductively coupled plasma spectroscopy(ICP)analysis showed that 96.76%-99.93%of La(?)in influent was removed.Analysis of morphology and energy spectrum confirmed that La(?)is toxic to AOB by limiting the synthesis of related enzymes in the ammonia oxidation process,destroying the original function of EPS,and inhibiting the growth of functional bacteria.Confocal laser scanning microscopy(CLSM),infrared spectroscopy(FTIR)and two-dimensional correlation spectroscopy further reveal the resistance mechanism of functional bacteria to La(?):prevents La(?)from entering cells via enhancing transport active and converts La(?)into lanthanum oxide(La2O3)and lanthanum nanoparticles using ?-polysaccharides and ?-polysaccharide-protein complex,respectively.(3)The long-term effects of rare earth elements(La(?))on the partial nitrification process have been explored through long-term exposure experiments.The addition of La(?)(0?5 mg/L)significantly reduces the performance parameter(NAR)of the process.Secondly,the excitation-emission matrices(EEM)analysis showed that the long-term treatment of La(?)gradually destroyed the stability of sludge particles by affecting the composition of extracellular polymer(EPS).Then,FTIR spectroscopy and EEM spectroscopy analysis confirmed that the long-term stress of high concentration(?5 mg/L)La(?)had an irreversible effect on the composition of EPS and functional groups.Moreover,the low dose(0-2.5 mg/L)of La(?)simultaneously promoted the growth of functional bacteria(Nitrosomonas)and the main competitor(Nitrospira),and significantly weakened the inhibitory effect of the pH-DO control strategy on NOB.Finally,bacteria reduce the biological toxicity of La(?)by enhancing the exocytosis of biomacromolecules such as glycans.(4)The nitrogen removal efficiency(NRE)of the Anammox process was temporarily reduced and then gradually recovered after the low concentration(?5 mg/L)La(?)treatment,but was decreased to a lower level(24.25±0.35%)after high concentration(?10 mg/L)La(?)treatment.High-throughput sequencing showed that La(?)significantly promoted the abundance of Anammoxoglobus(0.02%to 9.76%)at low concentrations(?5 mg/L),and significantly inhibited Anammoxoglobus(9.76%to 0.33%)at high concentrations(?10 mg/L).However,La(?)always inhibits the growth of Kuenenia.Then,the lack of cooperative bacteria limits the denitrification performance of Anammoxoglobus.Moreover,La(?)promotes the accumulation of propionate,which causes Anammoxoglobus replace Kuenenia as the dominant functional bacteria.