Isolation, Identification And Aerobic Denitrification Charateristics Of Two High Effiency Aerobic Denitrifers

Aerobic denitrification has been paid more and more attention in recent years, however,there is limited information on the mechanism of aerobic denitrification.Recently, aerobic denitrification bacteria such as Thiosphaera pantotropha and Alcaligenes faecalis have been intensively studied as potential microorganisms that may be used to overcome problems inherent in the conventional method.For obtaining more aerobic denitrifers,the isolation and characteristic of new strains capable of high aerobic denitrification were conducted in the study.Two strains of facultative and gram negative aerobic denitriflers,coded as ZW23 and ZW27,were isolated from flooded paddy soil and active sludge,respectively.In the light of their morphological and physiological features as well as the 16S rDNA sequences,they were identified as Pseudomonas pseudoalcaligenes and Pseudomonas mendocina.Under the aerobic incubation condition at 37℃,N loss through denitrification in the liquid culture medium inoculated with ZW23 and ZW27 both reached to 66%within12 hours, respectively.Correspondingly,N removal rates were 21.7 mg·l^-19h^-1 and 22.3 mg·l^-1·h^-1, respectively,which was much higher than those reported by other researchers.It was found that a part of total nitrogen was assimilated completely by the denitrifiers.Nitrite and ammonia weren't observed during the incubation.Obviously,strains ZW23 and ZW27 are two typical facultative aerobic denitrifiers of high efficiency in the removal of N in cultural medium.The strains ZW23 and ZW27 displayed denitridication under both aerobic and anaerobic conditions,but denitrification efficiency under aerobic condition(66%and 62%) was much lower than that under anaerobic condition(90%)..Strain ZW23 growing in the medium containing NH₄⁺-N as the sole nitrogen source could remove more than 95%of NH₄⁺-N in 36h.However,strain ZW23 had not the function of heterotrophic nitrification. Aerobic denitrifacation rate increased from 0%to 65%with the increase of the nitrate concentration for 50 to 400 mg·l^-1 in cultural medium.Strains ZW23 and ZW27 could also grow and showed aerobic denitrification ability in the medium containing NO₂^--N as the sole nitrogen source.In addition,strain ZW23 could simultaneously utilize both NH₄⁺-N and NO₃^--N.Moreover,the addition of NH₄⁺-N could accelerate aerobic denitrification speed of strain ZW23.For aerobic denitrification,optimum growth temperature of strains ZW23 and ZW27 was 32℃to 37℃.When initial pH of the mediums was 6.0-8.0,pH didn't affect the efficiency of aerobic denitrificaion of ZW23 strain with about 57%-60%of aerobic denitrification rate.The strain ZW23 could not grow under the initial pH 5.0.Carbon source could affect aerobic denitrification seriously,and the optimum C/N ratio for aerobic denitrificaion was between 10-15.In this study,we also investigated the application potential in wastewater treatment by the two aerobic denitrifiers ZW23 and ZW27.It was found that the two strains could improve total nitrogen removal efficiency of the wastewater by 10-20%.