Research On The Performance And Mechanism Of Aerobic Granular Sludge For Denitrification And Heavy Metal Removal

The wastewater from rare earth mines in southern Jiangxi has the characteristics of low organic concentration and high ammonia nitrogen and even contains toxic and harmful metal ions.It has become an important source of local surface water quality exceeding the standard.The practice has shown that traditional biochemical technology has disadvantages such as complex processes,difficulty in autotrophic bacteria enrichment,high treatment cost,and poor toxicity resistance when treating the wastewater.Aerobic granular sludge（AGS）has excellent characteristics such as high biological density,good sedimentation performance,high toxicity resistance,and simultaneous nitrogen and phosphorus removal.It has the potential to achieve single-stage denitrification and heavy metal adsorption.It provides a new idea for the efficient treatment of ionic rare earth mine wastewater.However,the current research on the treatment of ionic rare earth mine wastewater by AGS is still very scarce,resulting in a lack of sufficient understanding of how to achieve the coupling of different denitrification functional bacteria in AGS,which is also the energy-saving and consumption reduction and heavy metal ions in the treatment of ionic rare earth mine wastewater.Adsorption adds uncertainty.On the basis of rapid culture and stability study of autotrophic nitrification granular sludge（ANGS）in the laboratory,this thesis studies the storage and recovery effects of ANGS,examines the denitrification and heavy metal adsorption performance of ANGS,reveals the mechanism of ANGS adsorbing copper ions and lead ions,and explores the enhancement performance of AGS coupling denitrification with external carbon source:（1）The mature ANGS was stored in wet storage at room temperature for 40 days,during which the physical and chemical properties of ANGS after storage have significantly deteriorated.After re-aeration of the stored ANGS and adding exogenous nitrifying bacteria,the recovery of ANGS was successfully achieved within 27 days.Although obvious particle fragmentation was observed during the recovery process,it benefited from the attachment and growth of exogenous nitrifying bacteria.Particle fragments gradually transform into dense particles.The ANGS after successful recovery showed better short-cut nitrification and denitrification performance.The double reciprocal method was used to fit the kinetic parameters of AOB and NOB in ANGS,and it was found that the affinity of AOB to NH₄⁺was much higher than that of NOB to NO₂^-.Flora analysis showed that Nitrosomonas（AOB）increased from 17.27%to 51.15%,becoming the absolute dominant strain in nitrification granular sludge,The recovered ANGS was transported to another laboratory 1085 km away,and the stability was successfully restored within 10 days after re-aeration,which verified the possibility of ANGS recovery in a remote location.（2）A/O（anaerobic/aerobic）mode（M₁,M₃,M₅,M₇,M₉）and O/A（aerobic/anaerobic）mode(M₂,M₄,M₆,M₈,M₁₀)were examined separately.Under the denitrification performance of ANGS,it was found that in the 360min reaction process,in addition to the ammonia nitrogen removal rate,the nitrite accumulation rate,TIN removal rate,and simultaneous nitrification and denitrification rate in the alternating aeration mode are all higher than the full aeration（M₀）.Comparing the ammonia nitrogen removal rate,NAR accumulation rate,TIN removal rate,and SND efficiency under different alternating modes,it is found that the A/O mode is significantly better than the O/A mode.Among them,the M8mode has the highest nitrogen removal efficiency（52.12%）,indicating that ANGS has certain endogenous denitrification ability.Besides,compared with the full-course aeration mode,each alternate aeration mode has obvious advantages in energy saving.（3）The denitrification performance of AGS endogenous nitrification and denitrification and nitrification and denitrification coupled under the"aerobic-anoxic/external carbon source-aerobic"operation mode was study.The TIN removal rate of the system under the aerobic-anoxic mode was only around 60%,and after changing the operating mode,the system’s denitrification efficiency was significantly improve,reaching more than 90%.After the system is stable,the SVI remains at 35.00 mg/L,while the SV30/SV5 has little change,and remains between 0.9 and 1.0.MLSS was stable at about 5650 mg/L,and MLVSS/MLSS showed a significant increase overall（0.56-0.72）.The changes of EPS and PN/PS gradually tended to be flat（54.62～67.33 mg/g MLSS and 0.38～0.30）.The average particle size is stable around 1.6 mm.The dominant particle size is concentrated between 1.43～2.00 mm（30.86%）and 2.00～3.00 mm（28.64%）.The changes of SOUR_H（2.28～5.37mg O₂/g MLVSS）and SOURN（10.38～13.62 mg O₂/g MLVSS）were relatively stable,while SOURH/SOURN increased significantly（0.53～1.16）.After that,combined with the beaker experiment,it was found that the contribution of exogenous denitrification was 46.02±0.28%.Finally,compared with full aeration,it can save about 31.6%of aeration energy,41.33%of external carbon source,and 66.67%of alkalinity compensation,respectively.（4）Using ANGS as the adsorbent,single-factor experiments are carry out to study the influence of copper ion concentration,adsorption time,sludge concentration,stirring speed,and temperature on the adsorption effect.Finally,it was conclud that the stirring speed,time,and sludge concentration have a significant effect on the adsorption effect.Affect.On this basis,the optimal working conditions of adsorption are coupled by response surface method:time（A）=2.50 h,rotation speed（B）=125 r/min,sludge volume（C）=5250 mg/L,the predicted removal rate is 87.95%.The results show that ANGS exhibits strong tolerance and stability in heavy metal wastewater,and the granulation rate is maintained above 93%at different concentrations.The degree of fit of the Langmuir isotherm equation is R2_Cu=0.999,and the maximum adsorption capacity can be described as Qmax=15.02 mg/g,indicating that ANGS is typical monolayer adsorption for Cu²⁺;in the fitting process of the Freundlich isotherm equation,the correlation coefficient R²_Cu=0.969.Among them,1/n=0.1305,indicating that ANGS has a strong adsorption capacity for Cu²⁺;the higher degree of fit also indicates to a certain extent that the adsorption of Cu²⁺by ANGS is a complex physical and chemical process.（5）The effects of initial Pb（II）concentration,particle concentration,reaction time,and p H on the adsorption of lead by ANGS were studied.Single-factor experiments found that adsorption time,sludge concentration,and p H had a significant effect on the adsorption efficiency of ANGS.The optimal adsorption parameters were determined by response surface method:reaction time was 2.03 h,particle concentration was 6061.98 mg/L,p H was 3.01,and the predicted Pb（II）removal rate was 100.33%.The maximum adsorption capacity fitted by Langmuir isotherm is 39.84 mg/g MLSS,and the pseudo-first-order kinetic model can accurately describe the adsorption process.Combining SEM-EDS,FTIR,and XPS to characterize ANGS before and after adsorption,it is found that the adsorption of lead by ANGS is a complex physical and chemical process,including ion exchange,surface complexation,and electrostatic adsorption.