Study On The Construction Of Aerobic Denitrifying Bacteria And The Denitrification Performance Of Enhanced A/O Process

A/O process is one of the widely used biological denitrification processes for municipal wastewater However,since nitrification and denitrification in traditional biological denitrification need to be carried out under two different conditions,aerobic and anoxic,the nitrification liquid in the A/O treatment system usually needs to be returned to the anoxic section for denitrification,which leads to low denitrification efficiency and high operating energy consumption of the process.Therefore,how to improve the denitrification efficiency of the traditional A/O process and reduce its energy consumption has become a research hotspot of many scholars.In this paper,several high-efficiency aerobic denitrifying bacteria were screened out from activated sludge,and experimental studies were carried out on the denitrification characteristics and denitrification pathways of the strains,the optimal combination of compound bacteria,and the enhanced denitrification of activated sludge coupled with compound bacteria.On this basis,highly efficient immobilized aerobic denitrifying bacteria were constructed and applied to an A/O reactor operating under low mixed liquor reflux ratio conditions,and the effects of exogenous enhanced bacteria on the efficiency of nitrogen and phosphorus removal and system stability of the A/O process were investigated,aiming to provide a partial theoretical basis for the application of aerobic denitrifying bacteria in the enhanced denitrification of A/O process.The main research contents and conclusions are as follows:(1)Three strains with heterotrophic nitrification-aerobic denitrification function,AD-1,AD-2 and AD-5,were screened out from the activated sludge of wastewater treatment plant by isolation and purification,and identified as Pseudomonas sp.,Delftia sp.and Acinetobacter sp.after 16Sr DNA sequencing and phylogenetic analysis;The TN removal rate of AD-1,AD-2 and AD-5 could respectively reach 81.98%,92.65%and 95.21%,after incubation with 40 mg/L ammonia nitrogen as the nitrogen source at C/N of 8,30?and 120r/min for 24h;Under the same culture conditions,the TN degradation rates of AD-1,AD-2and AD-5 could respectively reach 91.18%,75.13%and 71.7%,with 40mg/L nitrate as the nitrogen source;Ammonia monooxygenase(AMO),hydroxylamine oxidase(HAO),nitrate reductase(NAR),and nitrite reductase(NIR)activities were assayed for AD-1,AD-2,and AD-5,respectively,and combined with the denitrification intermediates,it was hypothesized that the denitrification pathways of AD-1 and AD-2 were NH₄⁺-N?NH₂OH?NO₂^--N?NO₃^--N?NO₂^--N?(NO?N₂O)?N₂,the main denitrification pathway of AD-5 is NH₄⁺-N?NH₂OH?(NO?N₂O)?N_2.(2)The three strains screened were optimally combined with two other highly efficient aerobic denitrifying bacteria,DB-11 and Z1,to obtain the compound bacteria AD-1+AD-5+Z1 with the best denitrification efficiency.The simultaneous nitrification and denitrification characteristics of the compound bacteria and the individual bacteria were studied,and it was speculated that these three bacteria use ecological niche differences to complement each other in denitrification functions,forming an efficient and complete nitrogen metabolism pathway,thereby performing coordinated denitrification;The environmental impact factors of the compound bacteria were explored,and the results showed that when NH₄⁺-N is used as the sole nitrogen source,the optimal denitrification conditions of the compound bacteria are 30°C,initial p H of 8.0,rotating speed of 150 r/min,sodium citrate as carbon source,and C/N of 10;when NO₃^--N is the only nitrogen source,the optimal denitrification conditions for the compound bacteria are 30°C,the initial p H of7.0,the rotation speed of 120 r/min,sodium acetate as carbon source,and C/N of 10.(3)Coupling the compound bacteria AD-1+AD-5+Z1 with activated sludge for denitrification after being membrane attached,the results showed that the removal rates of COD and TN increased by 7.33%and 20.84%,respectively,compared with the control group,which were much higher than those of 2.21%and 2.97%when the compound bacteria were directly applied.Changes in the Alpha diversity index indicate that after bioaugmentation,the species abundance and diversity of activated sludge have decreased;The composition of the community structure at the Genus level showed that the content of exogenously enhanced bacteria in activated sludge increased from 0.15%and 0.00%to 2.43%and 1.32%,respectively.Flavobacterium,Corynebacterium,Brevundimonas,unclassified Rhodobacteraceae and Caldilineaceae have become the dominant genera,forming a new stable denitrification system in activated sludge.(4)The nitrification fluid reflux ratio of the A/O reactor in stable operation was reduced from 200%to 50%for activated sludge domestication,and after domestication,the effluent COD,TN and PO₄^3--P removal rates changed from 87.50%,91.08%and 56.91%to 92.19%,67.52%and 72.37%,respectively;After 50 days of bioaugmentation by adding film-hanging filters,the effluent COD,TN and PO₄^3--P concentrations decreased from 31mg/L,13.19mg/L and 2.27mg/L to 15mg/L,4.43mg/L and 1.84mg/L,respectively,and the removal rate was increased by 4.06%,22.85%and 7.41%respectively compared with those before adding;The TN removal rate in the aerobic pond before and after the bioaugmentation was analyzed,and the results showed that the simultaneous nitrification and denitrification efficiency in the aerobic pond increased by 28.34%compared with that before the bioaugmentation,and increased by 35.69%compared with that before the mixture reflux ratio was reduced,and by reducing the nitrification liquid reflux ratio,the electric energy consumed by the reflux pump can be reduced by about 60%.