| Bioaugmentation technology is a kind of efficient and economical method to improve the nitrogen removal,however,there are a lot difficulties caused by environmental factors in practical applications,for example,it may be ineffective or even fail.In order to promote the nitrogen removal by bioaugmentation technology,the nitrifying bacteria cultured rapidly by a self-developed method in this study was used to enhance nitrogen removal.The reasons for the loss of functional bacteria in bioaugmentated system and the mechanism of nitrogen removal promoted by autotrophic nitrifying bacteria or heterotrophic nitrifying bacteria were studied.Then combined these two different metabolic types of nitrifying bacteria for the nitrogen removal upgrade process in municipal WWTP.The above results can provide theory and practical support for the promotion and application of the enhanced nitrogen removal by biological.First of all,using activated sludge from ecological WWTP of LiaoZhong district as inocula,this study elucidated the effect of different types of fillers and different physical properties of fillers on the nitrifying bacteria enrichment by gradually increasing the NH4+-N concentration of influent(up to about 1000 mg/L).Results showed that coal ash was the specific filler for nitrifying bacteria adhering because of the higher abundance of ammonia oxidization bacterial(AOB),Nitrosomonas(46.33%),and ammonia oxidation efficiency(95.84%)in the system.The amount of AOB in this system was 30 times higher than in the initial sludge.The physical properties of coal ash(specific surface area and hydrophilicity of the fillers)also would affect the enrichment performance of nitriying bacteria.Nitrite oxidization bacterial(NOB)content in each system was effective restricted by high free ammonia(FA)concentration resulting from high NH4+-N load in infulent and alkaline pH.Then the abundance of NOB was improved through adjust NH4+-N load in infulent,and the complete nitrification process was achieved in the end.Based on the above results,this study established a new method for nitrifying bacteria enrichment with coal ash as fillers,which make nitrifying bacteria can be successfully enriched with large-scale and lowcost.The kinetic parameters of the maximum degradation rate of substrate(Vmax,108.91 mg/(L·h))and the half-saturation constant(Ks,63.71 mg/L)both were solved according to the basic model of Mond at 20?.Meanwhile,the environmental factors f(pH,DO,T)was considered to modify the basic model of Mond.Combined with the single factor experiment results,including pH,dissolved oxygen(DO)and Temperature(T),and orthogonal experiment results,the environmental factors f(pH,DO,T)was fitted by multiple non-linear curve(R2=0.999)with the 1stOpt software and statistical means.The accuracy of the kinetic model was verified well by actual sewage treatment in laboratory at 1.5-6.5 mg/L DO.A high efficiency and less energy consumption in the lab-scale anaerobic/anoxic/oxic(A2/O)process for sewage treatment were achieved with the sludge recycle ratio,internal recycle ratio and DO concentration of 80%,100%and 2 mg/L,respectively.In addition,load control was the effective measure to control the sludge bulking in A2/O system.In order to investigate the feasibility and the nitrogen removal process mechanism of the bioaugmentation technology by using autotrophic nitrifying bacteria and heterotrophic nitrifying bacteria,the efficiency and microbial community structures in A2/O system feeding with simulate sewage were studied.The results showed that 5%(v/v)of adherent autotrophic nitrifying bacteria can significantly reduce the loss of it in bioaugmentated system,and the final AOB and NOB abundance were 7.85 and 17.88 times of the sludge before bioaugmentation after 42 days' continuous and stable operation.The additional autotrophic nitrifying bacteria has contributed to 23.91%and 16.99%of the NH4+-N and TN removal efficiency,respectively,with 94.25%and 84.31%of the NH4+-N and TN removal efficiency in the bioaugmentated system.The bioaugmentated system with heterotrophic nitrifying bacteria was still efficient even under the condition of low C/N ratio(3:1),with NH4+-N and TN of 93.07%and 66.71%.The community structure analysis showed that the additional heterotrophic nitrifying bacteria was decreasing in the bioaugmentated system,on the contrary,the aboriginal AOB(Nitromomonas)and NOB(Nitrospira)were on the rise,with a increase to 1.50%and 2.32%,respectively.The theory,the indigenous autotrophic nitrifying bacteria can be improved by the additional heterotrophic nitrifying bacteria in bioaugmentated system under the condition of low C/N ratio,fill the gap of heterotrophic nitrifying bacteria promoting the nitrogen removal in low C/N ratio system.On the other hand,this study clarified that the immediate cause of poor nitrogen removal efficiency was the shortage of nitrifying bacteria in the municipal WWTP basing on the long-term treatment performance and the microbial community sturcture detected by high-throughput sequencing technology of the system.The synergistic-bioaugmentation technology by autotrophic nitrifying bacteria and heterotrophic nitrifying bacteria was put forward to against this problem,the operating paramters was adjusted to assist the upgrade process of nitrogen removal in WWTP at the same time.After the inoculation with autotrophic nitrifying bacteria of 5%(v/v)and with heterotrophic nitrifying bacteria of 0.8%(v/v),the long-term stable and high removal efficiency was achieved in upgraded WWTP after 25 days' cushion(the effluent concentration of COD and NH4+-N were 21.99 mg/L and 1.61 mg/L,respectively),even under the condition of low temperature(<12?).The promotion of synergistic-bioaugmentation technology for COD and NH4+-N removal rate was 10.5%and 71.51%,respectively.Microbial community structure analysis showed that the abundance of AOB and NOB increased significantly after long-time operation,which was 7.35 and 17.8 times of them after just inoculation.The experience in engineering paractice and theoretical research in this study provieds powerful instruction and reference for the nitrogen removal upgrade process in municipal WWTP,meanwhile,it gives evidence for the extensive application of the nitrogen removal bioaugmentated by microorganism. |
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