Characteristics Of Nitrogen Removal Performance,Biofilm Formation And Its Application In Biofilm-SBR By Pseudomonas Stutzeri XL-2

With the development of the national economy,a large number of nitrogenous substances discharged because of human production and living activities,these nitrogen not only destroyed the aquatic ecological environment,but also a serious threat to human health.The efficient and economical removal of nitrogenous pollutants is a difficult problem to be solved at present.Due to the low rate of nitrification,the complex structure and time-consuming of traditional traditional biological nitrogen removal method,it can not meet the requirement of high-concentration nitrogen-containing wastewater treatment.In recent years,with development of heterotrophic nitrification-aerobic denitrification theory,a simple and quick way for biological nitrogen removal was achieved.In this study,the nitrogen removal performance and biofilm formation characteristics of Pseudomonas stutzeri XL-2 were studied.On this basis,the optimum environmental conditions for the biofilm formation of strain XL-2 were investigated,and then the bacteria were added to the biofilm-SBR reactor to investigate the effect of the biofilm formation and the nitrogen removal of the global filler in biofilm-SBR,which provides a theoretical basis and technical support for the application of both the biofilm forming ability and the denitrification capacity in the actual sewage treatment system.The nitrogen removal properties of Pseudomonas stutzeri XL-2 were investigated in different nitrogen sources.The results showed that strain XL-2 had a good heterotrophic nitrification-aerobic denitrification ability.In the 50 mg/L NH4+-N medium,the strain XL-2 showed heterotrophic nitrification and aerobic denitrification,and the removal rates of removal rates of NH4+-N and TN were 53% and 47% respectively;in the 20 mg/L NO3--N medium,the strain XL-2 showed high aerobic denitrification ability,and the removal rates of NO3--N and TN were 87.4% and 65.4% respectively in 9 hours,the largest removal rate of NO3--N was 2.48 mg L-1 h-1;in the 20 mg/L NO2--N medium,strain XL-2 also showed high aerobic denitrification ability,the NO2--N removal rate was 99.9% within 12 hours,the average removal rate of NO2--N was 2.34 mg L-1 h-1;the strain XL-2 was able to nitrification and denitrification simultaneously in 50 mg/L NH4+-N and 20 mg/L NO3--N mixed nitrogen source medium,the removal rates of NH4+-N and TN were 99% and 94% respectively,were higher than those in single nitrogen sources.We study the biofilm formation ability and cell characteristics（motility,hydrophobicity,autoaggregation ability and EPS）in the microtiter plate,the results showed that the strain XL-2 could form biofilm on the inner surface of the micro-plate and the liquid medium,and the biofilm formation was the highest at 24 h after culture,and the strain XL-2 not only had strong swimming ability and cluster swarming ability,but also had capability of twitching motility;the strain XL-2 has strong autoaggregation ability,hydrophobic ability and high extracellular polymer（EPS）content,further analysis shows that the variation trend of autoaggregation ability,hydrophobicity and protein of EPS highly consistent in the process of strain growth.The autoaggregation ability,hydrophobicity and flocculation ability of strain XL-2 were significantly promoted by TB-EPS.We have studied the environmental factors on biofilm formation,the optimum conditions were as follows: the optimal temperature was 30 ℃,the optimum pH was 7,the optimum carbon source was acetate,the optimum Ca²⁺ and Mg²⁺ concentrations were 1 mM and 10 mM,respectively.The amide group of protein and polysaccharide,nucleic acid group is the main functional group of EPS adsorption Mg²⁺;amide group of protein is the main functional group of EPS adsorption Ca²⁺.In addition,1 mM Ca²⁺and 10 mM Mg²⁺ not only improved the hydrophobicity and autoaggregation ability of strain XL-2,but also significantly enhanced the flocculation of EPS.The strain XL-2 was added to the biofilm-SBR to investigate the effect of the biofilm formation and the nitrogen removal of the global filler in biofilm-SBR.The results showed that the biofilm formation rate of the global filler and the denitrification capacity in the reactor SBR1（adding strain strain XL-2）were significantly higher than that of the reactor SBR2（without strain XL-2）.During the process of the biofilm forming,the removal rate of NH4+-N,TN and COD in two reactors increased with the increase of the amount of biofilm formation.The NH4+-N removal rate of SBR1 was about 3% higher than SBR2,COD removal rate was about 5¹0% higher than SBR2,TN average removal rate was about 10% higher than SBR2.Under different concentrations of NH4+-N,the removal efficiency of NH4+-N and COD in the two reactors was almost no difference,which could be maintained at about 94% and 90% respectively.However,NO3--N and NO2--N in SBR2 reactor were much higher than SBR1,and TN removal rate was about 10% lower than that of SBR1.