Effect And Stability Of Nitrogen And Yttrium Removal By Aerobic Granular Sludge In Rare Earth Tail Water

Ionic rare earth mine tailings are characterized by acidity,inorganic,high ammonia nitrogen,and even yttrium(Y³⁺),which has become an important pollution source of regional water environment.Physical and chemical treatment of the wastewater has some shortcomings such as high operating cost and easy to produce secondary pollution.In contrast,biochemical methods are relatively cheap to run and easy to maintain.However,the traditional biochemical treatment of the wastewater has the defects of high demand for external carbon sources and low tolerance of heavy metals.Aerobic granular sludge（AGS）is a new wastewater treatment technology.Its unique stratified structure and high toxicity resistance make it capable of simultaneous nitrogen and heavy metal removal,which provides a new idea for the treatment of ion-type rare earth mine tailings.The objective of this study is to achieve simultaneous nitrogen and yttrium removal in AGS,and the specific research contents are as follows:The stability of AGS in five different influent nitrogen loading environments of 0.2,0.4,0.8,1.2 and 1.6 kg/m³·d was studied.Firstly,the removal performance of AGS was observed during the 30-day inorganic wastewater treatment process,and then the sludge composition,physicochemical properties and microbial community were measured at the end to reveal the stability rule.The experiment showed that AGS cultured at 0.8-1.2 kg/m³·d had better particle structure and sedimentation performance.Under the condition of 0.2-1.2 kg/m³·d,the removal rate of ammonia nitrogen is maintained between 80%and 100%,the removal rate of TIN fluctuates between 0 and 40%,and the removal rate of ammonia nitrogen decreases（50-70%）under the condition of 1.6 kg/m³·d.AGS can use protein（PN）,soluble polysaccharide（PS）and fat as endogenous carbon to promote denitrification.The growth and metabolism of nitrifying bacteria and denitrifying bacteria were relatively balanced at 0.8-1.2 kg/m³·d nitrogen loading.The enhancement effect of external organic carbon source on heterotrophic denitrification of autotrophic nitrification granular sludge（ANGS）was studied.First,the effects of three factors（carbon source concentration,aeration rate and aeration stop ratio）on the removal rate of total inorganic nitrogen（TIN）were explored and their suitable operating range was determined.Then,the response surface method was used to couple the optimal operating conditions and simulate the degradation kinetics of matrix.The results show that when the chemical oxygen demand（COD）dosage is 600 mg/L,the aeration rate is 0.6 L/min,and the aeration stop ratio is 9:21,the nitrogen removal effect is the best 69.39%.Kinetic fitting showed that ANGS had the best affinity for nitrate nitrogen（K_s=10.71 mg/L）.The contribution rate of exogenous nitrification and denitrification to TIN removal in ANGS was85%,while endogenous nitrification and denitrification accounted for 15%.The nitrogen removal effect of AGS under different alkalinity and carbon source concentration was investigated.First,the nitrification effect,duration of nitrification reaction and p H changes of AGS at different dosages of alkalinity were investigated,and then the denitrification effect and p H changes of AGS at different dosages of external carbon sources were investigated.It was found that with the increase of alkalinity,the effluent p H of nitrification solution increased,ammonia nitrogen decreased（79.2-19.2 mg/L）,and the duration of nitrification reaction extended（50-150 min）.Alkalinity and exogenous carbon source had important effects on simultaneous nitrification and denitrification of AGS.When the carbon source concentration and alkalinity were above 280 mg/L and 8 mmol/L,the TIN removal rate basically did not change（85%）.The effects of fluctuating ammonia nitrogen inlet water and in situ ultrasonic on AGS stability in inorganic high ammonia nitrogen wastewater were explored.Firstly,the influence of ultrasound on the physical and chemical properties,decontamination properties and microflora structure of AGS was explored,and then the nitrogen load fluctuation was conducted to investigate the gain effect of ultrasound on the stability of AGS treatment.The study found that the inoculated sludge on 1-95 days experienced the process of disintegration before granulation.The ultrasonic combined control group completed granulation on day 80and 40 days,respectively,and the ultrasonic group particles were more loose,and the nitrogen removal performance of the ultrasonic group and the control group was very close（80%）.On day 96-140,100-500 mg/L ammonia nitrogen load fluctuated,which had no obvious impact on sludge volume（MLSS）,sludge volume index（SVI）and granulation rate,but the removal efficiency of ammonia nitrogen and TIN had transient fluctuations（70%-100%）.The nitrification/denitrification rate in the ultrasound group was better than that in the control group（24.1 mg N/（g SS·h）and 27.0 mg N/（g SS·h））,and had a smaller particle size and more dense structure.Community analysis found that sonication promoted the proliferation of the genus denitrifier.The desorption effect of AGS on yttrium ion(Y³⁺)was explored.Firstly,the influence of initial concentration,p H,salinity,coexisting ions and particle size on the adsorption process under aeration conditions,then kinetic and thermodynamic fitting of the adsorption process,and finally AGS was recovered by desorption test.It was found that when the initial Y³⁺mass concentration,AGS can completely adsorb Y³⁺in wastewater is<50 mg/L.The adsorption of Y³⁺by the AGS agrees with the pseudo-secondary model and the Langmuir model,indicating that the process is a monolayer adsorption process and the chemisorption plays a dominant role.XPS characterization found that the adsorption functional groups are ester,carboxyl and amino groups.NH₄Cl is a mild desorption agent,and the efficiency of 5 repeated adsorption-desorption is still 50%.The effect and stability of yttrium removal in granular sludge（MBGS）were explored.MBGS was first domesticated under aeration conditions,and then Y³⁺was added to investigate the stability changes of MBGS and the migration rules of the microflora structure.The study found that at the initial addition of low concentration Y³⁺stage（<8 mg/L）,the particle size of the sludge became larger,the structure became more dense,and a better total nitrogen removal rate（>90%）was maintained.However,with the increase of Y³⁺concentration（8-20 mg/L）,the toxicity to MBGS system gradually appeared,mainly manifested by the decrease of EPS secretion,the decrease of oxygen consumption activity and nitrogen removal rate,and the TIN removal rate gradually decreased to 50%after 150 days.When the inlet Y³⁺concentration increased to 20 mg/L,the adsorption capacity of MBGS pair decreased to 60%.Y³⁺was highly toxic to the nitrification bacteria Armatimonadetes＿gp 5and the green algal fungus Chlorophyta.