Study On Cultivate And Process Characteristics Of Denitrifying Granular Sludge

Nitrogen pollution has always been a key concern of the society.It mainly exists in three forms as ammonia,nitrate and organic nitrogen,of which nitrate remains stable in the aerobic environment.In addition,organic toxic pollutant,like phenol,exists in the production wastewater of coking,petrochemical and other industries.Toxic phenol inhibits the activities of microorganisms,thus increasing the limitation of biological denitrification,which has become one of the difficulties in the nitrate-rich wastewater treatment.In view of this,this thesis studied the cultivation and enrichment of denitrifying granular sludge,effect of different particle size diameter on the sludge characteristics and microbial community structure on the denitrifying granules and the performance of denitrifying granular sludge treating phenol-containing wastewater to finally realize the efficient removals of nitrate and phenol,which can provide theoretical guidance for efficient and stable operation of denitrifying granular sludge process.The main conclusions are as follows:（1）In the Upflow Sludge Blanket（USB）reactor,flocculent activated sludge was inoculated to enhance the enrichment of denitrifying granular sludge by adjusting the substrate concentration and increasing the ascending flow rate.After 45-d operation,denitrifying granular sludge featured with clear edges,milky white and uniform particle size was rapidly cultivated.After the formation of denitrifying granular sludge,the total nitrogen removal load（NRR）and carbon removal load（CRR）reached 0.65 and 1.97kg/（m³·d）,respectively,and the maximum specific degradation rates of NO₃^--N and COD were 68.90 and 182.63 mg/（g MLSS·d）,respectively,indicating that the denitrifying granular sludge process exhibited a good nitrogen and carbon removal performance.In the cultivation process of denitrification granular sludge,the average△COD/△NO₃^--N ratio（C/N ratio）remained 3.35,which was always higher than the theoretical value of 2.86.The extracellular polymer substance（EPS）content,protein（PN）and polysaccharide（PS）fractions of EPS,and PN/PS ratio also increased gradually,which made the microorganisms to exhibit hydrophobic.At the same time,three-dimensional fluorescence spectrum（3D-EEM）analysis results showed that tryptophan,tyrosine and other proteins played important roles in accelerating the rapid formation of denitrifying granular sludge.（2）Four groups of denitrifying granular sludge with different particle sizes were screened out in the USB reactor in stable operation,which were S1（<0.5 mm）,S2（0.5～1.0 mm）,S3（1.0～1.5 mm）and S4（>1.5 mm）,respectively.The physicochemical characteristics,denitrification activities and microbial community structures of four-group granular sludges were comprehensively investigated.The results showed that the removal rates of NO₃^--N and COD in the four groups of granular sludge were above 94%and 69%,respectively,and the removal efficiency,integrity coefficient and PN/PS ratio of S3 were higher than those of S4.In addition,from the results of EDS,it was observed that the Ca²⁺content of S4 was 21.18%,and the calcification was serious,which was not conducive to mass transfer.The diversity and richness of microbial community were positively correlated with particle size,and nar G and nir S played more important roles in denitrification.Give that the physicochemical characteristics,degradability and microbial community of denitrifying granular sludge with different articles,granular sludge with the particle size of 1.0～1.5 offers the best performance for the stability and high efficiency of the system.（3）In the stable operation of the USB reactor,the dosage of phenol was gradually increased and the dosage of sodium acetate was decreased with a C/N ratio kept at 4.0.After 56-day acclimation,the removal rates of NO₃^--N and phenol are over 90%and70%,respectively,and the PLR and PRR were 0.101 and 0.067 kg/（m³·d）,respectively,which indicated that the acclimated denitrifying granular sludge showed a good denitrification and phenol removal performance.With the increase of phenol dosage,the particle size of granular sludge increased,and the percentage of 0.5～1.5 mm sludge increased from 53.94%to 67.9%.Meanwhile,the contents of LB-EPS and TB-EPS increased from 15.24 and 24.11 to 21.79 and 43.24 mg/g,respectively,and the hydrophobic PN accounted for a relatively high proportion.The degradation kinetics of phenol were investigated using Monod equation,and the V_maxand K values were 0.0105h^-1and 77.897 mg/L,respectively.