Performance Of Aerobic Granular Sludge For Simultaneous Nitrogen, Thallium And Yttrium Removal

Ionic rare earth mine tail water has the characteristics of acidic inorganic high ammonia nitrogen wastewater,and even contains heavy metal ions thallium（Tl（Ⅰ））and yttrium（Y（Ⅲ））,which has become an important pollution source of local water environment.The physicochemical treatment of the wastewater has some shortcomings,such as high operating cost and easy to produce secondary pollution,while the biochemical method has relatively low operating cost and simple maintenance.However,the traditional biochemical treatment of the wastewater requires continuous external injection of carbon sources,resulting in high operating costs.At the same time,heavy metal ions such as Tl（Ⅰ）and Y（Ⅲ）are toxic to water treatment microorganisms.Therefore,it is very challenging for biochemical method to realize simultaneous denitrification and removal of heavy metals from tailing water of ionic rare earth mines.AGS has the potential of simultaneous denitrification and heavy metal adsorption due to its unique layered structure and high toxicity resistance,which provides a new idea for the treatment of ionic rare earth mine tail water.The goal of this study is to achieve simultaneous nitrogen removal of thallium and yttrium by AGS.The specific results are as follows:The intermittent aeration operation mode of"stirring-aeration-stirring"was used to explore the formation law of AGS and its degradation effect on pollutants in wastewater with low C/N ratio（1 to 6）,so as to provide a carrier for domesticating ANGS.The sludge achieved aerobic granulation within 35 days,the granulation rate was about 90%,and the average particle size was 0.54 mm.The removal rate of ammonia nitrogen and COD by AGS is more than 90%,and the removal rate of TIN is about 50%.The lack of carbon source in denitrification leads to the low removal of TIN.The increase of influent C/N is beneficial to the growth of heterotrophic bacteria and promote the secretion of EPS so as to accelerate the formation of AGS.In the"stirring-aeration-stirring"operation mode,the aeration section is mainly the degradation of COD and the oxidation of ammonia nitrogen,and the contribution rates of exogenous denitrification and endogenous denitrification to TIN are 2.82%-18.45%and 18.30%-48.28%,respectively.Inoculated heterotrophic AGS was run in 4 parallel SBR（B₁:blank control group,B₂:adding 10 m L of nitrifying bacteria concentrate every cycle）B₃:adding Tl（Ⅰ）1 mg/L Magel B₄ every cycle:adding nitrifying bacteria concentrate 10 m L and Tl（Ⅰ）1 mg/L every cycle),domesticating simultaneous denitrification and removing thallium ANGS by gradually reducing COD to zero within 15 days.The ANGS in B₁,B₂,B₃ and B₄ was basically stable within 40,33,30 and 33 days,respectively,and the ammonia nitrogen removal efficiency was more than 90%after 33 days.The effluent TIN gradually stabilized after 36,32,32 and 36days.The removal efficiency of Tl（Ⅰ）by B₃ and B₄ was 59.5%and 57.1%respectively after30 days.The results showed that mature ANGS were successfully cultured in B₁,B₂,B₃ and B₄ within 40,33,33 and 36 days,respectively.The R² of the nitrogen degradation kinetics fitting curve of ANGS was more than 0.97.among them,the ammoxidation matrix semi-saturation constant(K_SN)and specific degradation rate(r _Nmax)of B₃ were the highest,112.16 mg/L and 73.86 h talk B₂ were similar to B₁,and B₄ was the smallest,and the maximum specific degradation rate(r _Nmax)and matrix semi-saturation constant(K_SN)of nitrite oxidation were B₃>B₄>B₁>B₂.The Freundlich equation was used to fit the adsorption of Tl（Ⅰ）on B₃ and B₄,and the results showed that R² was greater than 0.99.The adsorption capacity of Tl（Ⅰ）on B₃ was slightly higher than that of B₄,which was 0.4476 and 0.3845 respectively.XPS characterization showed that the characteristic peak of Tl_4f5/2 was detected at the119.0e V of B₃ and B₄,which confirmed the adsorption of Tl（Ⅰ）by ANGS.The high-throughput results showed that there was little difference in the species of dominant bacteria in ANGS,and the proportion of abundance was different,of which the most dominant genus was Nitrosomonas（about 32%）.ANGS（B₁,B₂,B₃and B₄）were stored at room temperature under 0,1,5 and 10mg/L Tl（Ⅰ）stress,respectively.The restored ANGS was placed under Tl（Ⅰ）stress to investigate the effect of ammonia nitrogen load on ANGS.After storage at room temperature for 40 days,some of the particles of ANGS blackened,but the overall structure and sedimentation performance did not change significantly.During storage,ANGS released ammonia nitrogen,nitrate nitrogen,COD and other pollutants into the liquid phase,and absorbed almost all Tl（Ⅰ）in the liquid phase.The SOUR_AOB of the stored ANGS decreased by 60%to 70%,to12.39-15.07 mg/g MLVSS;SOUR_NOB,decreased by 46%to 7.22-11.39 mg/g MLVSS.After storage,the abundance of Proteobacteria in the main dominant phyla of ANGS decreased,and the abundance of Bacteroidetes increased.The largest dominant genus of ANGS before storage was Nitrosomonas（32.54%）,and the abundance decreased after storage（A₁:1.10%,A₂:2.79%,A₃:3.06%,A₄:4.76%）.The higher the concentration of Tl（Ⅰ）,the better to retain the activity of nitrifying bacteria in storage.After storage,the ANGS recovered successfully in 13 days,and when the influent ammonia nitrogen gradually increased（100-1100 mg/L）,the removal rate decreased from 100%to about 50%.High p H stress caused rapid instability of ANGS,and the unstable ANGS system could be restored by inoculating ANGS with good activity.The dominant bacteria of stable operation of ANGS under Tl（Ⅰ）stress was Nitrosomonas（39.37%）,and the removal rate of 1mg/L Tl（Ⅰ）was about 70%.XPS characterization showed that Tl₂O or Tl CO₃ precipitation was detected on the surface of ANGS,and it was found that the C,O and Tl elements on the surface of ANGS running in inorganic ammonia nitrogen wastewater for a long time increased.The running stability of ANGS was investigated under the stress of 7 mg/L Tl（Ⅰ）and1.5,4 and 7 mg/L Y（Ⅲ）.During the operation,the average particle size of ANGS was about0.55,the SVI was kept between 28-34 m L/g,and the SV₃₀/SV₅ was always greater than 0.96.When 7 mg/L Tl（Ⅰ）was added in 15-30 days,the removal rate of ammonia nitrogen was always maintained above 90%.When 7 mg/L Tl（Ⅰ）was added in 15-30 days,the removal rate of ammonia nitrogen was always maintained above 90%.When 7 mg/L Y（Ⅲ）was added in30-45 days,SOUR_AOB decreased rapidly（28.45-6.61 mg O₂/（g VSS·h））,and the removal rate of ammonia nitrogen decreased from 90%to 40%.The secretion of EPS increased（364.94mg/g VSS）.After 45-70 days,the concentration of Y（Ⅲ）in the influent was reduced to 1mg/L,the ammonia-nitrogen removal rate gradually recovered（40%-90%）,the EPS decreased（94-45 mg/g VSS）,and 4 mg/L Y（Ⅲ）was added in 70-90 days,the ammonia-nitrogen removal rate decreased again（90%-40%）,and the SOUR remained at a low value（12 mg O₂/（g VSS h））.The removal rate of Tl（Ⅰ）by ANGS was 25%-62%,and that of Y（Ⅲ）was above 90%.XPS characterization results show that Y element may exist on the surface of ANGS in the form of precipitate or crystallization,and there are a large number of methylene,hydroxyl,carboxyl and amino groups on the surface of ANGS,which are the main functional groups for adsorbing Tl（Ⅰ）and Y（Ⅲ）.The results of high-throughput analysis showed that Tl（Ⅰ）stress caused the extinction of some bacteria,but also increased the abundance of Nitrosomonas,the main ammonia-oxidizing bacteria（36.8%-53.4%）,while Y（Ⅲ）stress decreased the abundance of AOB from 53.42%to 5.17%.Langmuir regression analysis of the isothermal adsorption of Y（Ⅲ）by ANGS shows that R² is 0.9998 and the maximum adsorption capacity is Q_max=39.84 mg/g,R_Lis 0.787,indicating that ANGS has good adsorption properties for Y（Ⅲ）.In order to establish AGS simultaneous denitrification and yttrium removal system,the effects of alternating aeration and external carbon source on AGS simultaneous nitrogen and yttrium removal were investigated.By adding anaerobic time period（alternating aeration）,inoculating part of AGS with denitrification function and adding carbon source during the operation cycle,the removal rate of total nitrogen by AGS is about 30%,the removal rate of COD is more than 90%,and the removal rate of Y（Ⅲ）is more than 88%.The XPS characterization results show that there are Y oxides,Y carbonates and Y elemental metals on the surface of AGS,which proves the adsorption of Y（Ⅲ）by AGS.The pseudo-second-order kinetic model fitted the adsorption process of Y（Ⅲ）by AGS,R²=0.9997,indicating that the control step in the adsorption process was chemical adsorption,and the maximum adsorption amount of Y（Ⅲ）by Langmuir equation was 0.9999,Q_max was 34.86 mg/g,indicating that AGS had good adsorption performance for Y（Ⅲ）.With the change of F operation mode and foreign investment of COD,the relative abundance of dominant bacteria Nitrosomonas decreased from 47.43%to 11.08%,while the relative abundance of Chryseobacterium,unclassified＿Chitinophagaceae,unclassified＿Comamonadaceae,Comamonas,Thauera and other bacteria increased.