Enhanced Nitrogen Removal By Heterotrophic Nitrification-aerobic Denitrifying Bacteria In Sequential Batch Reactor

Traditional biological nitrogen removal methods mainly rely on the combination of autotrophic nitrification and anoxic heterotrophic denitrifying bacteria,but its low ammonia oxidation rate and relatively harsh control conditions have led to increase the denitrification cost.Heterotrophic nitrification-aerobic denitrifying bacteria have attracted much attention due to their denitrifying ability under aerobic conditions.Recent studies on heterotrophic nitrification-aerobic denitrifying bacteria focuses on the screening of single strain and the test of its nitrogen removal performance,while the researches on composite bacteria are few and mostly intermittent experiments.The environmental adaptability of the single strain is weaker than that of the compound bacterium,which is susceptible to the interference of external environment.The compound bacterium has more advantages than single strain in treatment time and effect.Based on the screening heterotrophic nitrification-aerobic denitrifying bacteria,we combined with the changes of intermediate products,nitrogen balance calculation and enzymatic activity expression to investigate nitrogen removal mechanism of strains in this paper.The optimization of nitrogen removal conditions of compound bacteria by us to explore the effect of simultaneous nitrification and denitrification.Compound bacteria were added to SBR to construct a stable and enhanced synchronous biological nitrogen removal system,and then the effects of the addition of exogenous microorganisms on the effluent water quality of SBR,nitrification activity of sludge and Extracellular Polymer Secretion were studied.The high-throughput sequencing technology was used to investigate the dynamic changes of sludge microbial community structure in different periods.There are the main contents and conclusions as follows:?1?Two strains,S4 and S9,with heterotrophic nitrification-aerobic denitrification capacity were isolated from activated sludge and identified as Bacillus subtilis and Pseudomonas aeruginosa,respectively,which were able to use NH₄⁺-N,NO₃^--N,and NO₂^--N with CH₃COONa as the carbon source under aerobic conditions.Respectively the reaction rates were 6.5,4.28,3.78 and 6.82,5.21,5.4 mg/L/h.Based on enzyme activity combined with the intermediate products in the process of denitrification indicated that the two strains belonged to the heterotrophic nitrification-aerobic denitrification coupled denitrification pathway.Nitrogen balance analysis confirmed that the main way of nitrogen utilization was the denitrification of two strains,which accounted for 43.1%and 51.09%respectively.It's suggested that denitrification under aerobic condition was the main nitrogen removal pathway.The denitrification performance of the compound bacteria was better than that of the single strain.Among them,1:2?S4:S9?was the optimal combination,and the removal efficiency of NH₄⁺-N and TN were 99.83%and 92.7%,respectively.Compound bacteria tended to preferentially use NH₄⁺-N in mixed nitrogen sources,which has excellent simultaneous nitrification and denitrification performance.Under the conditions of rotation speed of 180 r/min,carbon-nitrogen ratio of 15 or concentration of ammonia of 100²00mg/L,the compound bacteria had the best denitrification effect.Haldane model fitting showed the optimal substrate concentration of 167.13 mg/L.?2?Two SBR?SBR1 and SBR2?were run in parallel.After exogenous microorganisms were added for a short period of adaptation,the effluent quality of SBR₁ was rapidly stable,and the average removal rate of COD and TN were increase by 12.11%and 12.06%,respectively,compared with the stable period.The presence of NH₄⁺-N and NO₂^--N were not detected in the effluent of SBR₁,and the average concentration of NO₃^--N was 8.34 mg/L in the late stage of enhancement,which was significantly lower than that of SBR₂?17.89 mg/L?in the control.The rate of ammonia oxidation of SBR₁?0.0402 mgO₂/?gMLSS·min??was significantly higher than that before inoculation?0.0332 mgO₂/?gMLSS·min??.There were obvious changes in TB-EPS yield and properties before and after bioaugmentation,in which the protein content increased significantly and humus decreased.The fluorescence intensity of each protein peak of TB-EPS was stronger than that of LB-EPS.Fourier transform infrared spectroscopy?FTIR?results showed that some peak positions in EPS migrated.?3?Sequencing results indicated that the addition of exogenous microorganisms significantly changed the structures of the microbial community in SBR.The sample dilution curve and the changes in the Alpha diversity index showed that the abundance of the flora had an increasing trending,and the diversity gradually decreased.Acinetobacter,Paracoccus,and other protozoa species gradually decrease in abundance,losing their dominant position in the competition.A new stable denitrification biological system was formed by Azoarcus,Roseovarius,and other bacteria in the late period of intensification,where the relative abundance of Bacillus and Pseudomonas were 1.4%and 10.3%,which was significantly different from the initial vaccination.