Study On SBBR One-step Completely Autotrophic Nitrogen Removal Process And The Microecological Characteristics

In the aspect of treating high ammonium and low C/N ratio wasterwater, one-step completely autotrophic nitrogen removal process is talent showing itself for the advantages of simplicity and high efficiency low consumption compared with other biological nitrogen removal processes. However, it is still on the stage of research and development. Some research achievements can not reach agreements for the limitation of micro-level mechanism understanding and short of analysis and detection technologies. Seeking the reaction mechanism from microecology view point has become one of the key factors which restrict this process come to engineering and needs to be overcome urgently.This paper will focus on the microecology characteristics of the SBBR one-step completely autotrophic nitrogen removal process. Microbial community structures between activated sludge and biofilm samples during the start-up and steady operate time will be analyzed for sake of the relationship between macroscopical control parameters and microbial composition. Meanwhile, the main fuctional bacterium will be identified. Some of their physiological and ecological characteristics as well as the ecological factors which influence their cooperating metabolism will also be analyzed.The experiment was carried out in four SBBR reactors. Two of the most representativeness ones were applied in this study. Reactor A which was operated under the condition of ammonia concentration 60~120mg/L, temperature 30±2℃, hydraulic retention time (HRT) 24h, pH 7.8～8.5 and dissolved oxygen (DO)0.8～1.0mg/L (continuous aeration) complished the nitrification start-up. Then ammonia concentration was adjusted to 60~120mg/L and intermittent aeration replaced the continuous way. Under the condition of DO 2.0(aeration)/ 0.4(non-aeration) mg/L, the similarity of microbial community structure between activated sludge and biofilm samples was low. The distribution of DO in activated sludge and biofilm made a suitable condition for different bacteria. Ammonium oxidation bacteria (AOB) and anerobic ammonium oxidation bacteria (ANAMMOX) were the preponderant bacterium in reactor A. Their co-metabolisms made ammonium oxidation and TN removal rate reach to 90% and 80% respectively. Reactor B, which was started up under DO of 1.5～2.0mg/L, worked with a low efficiency. The concentration of biofilm was low. There was not much difference between biofilm and activated sludge samples on the microbial community structure. The similarity reached to 100% and the variety of dominant bacteria was poor. Ammonium oxidation and TN removal rate only were 37% and 30% respectively. DO of 1.5～2.0mg/L(continuous aeration) was not beneficial to the elution of nitrite oxidation bacteria (NOB) during the start-up time.The microbial community structures of SBBR one-step completely autotrophic nitrogen removal process during the nitrification start-up time had changed a lot. The microbial flora of fungi, bacterial and actinomycetes also were analyzed. Result showed that the population, species, species number and dominates of microorganisms in this reactor were different from the inoculation sludge. When heterotrophic bacteria were washed out while autotrophic bacteria were accumulated, the sludge mainly was bacilliform floccule, but the sludge was petallike when the steady nitrification was set up and part nitrogen removal function was reached. The lack of organic carbon source made autotrophic bacterium become the dominates and the microbial community structures become simple. The populations of AOB NOB and ANAMMOX were greatly improved.The microbial community structures would be influnenced by aeration/non-aeration ratio, DO as well as pH. Results showed that bacterial richness values of biofilm were higher than activated sludge in 2h: 2h aeration/non-aeration ratio, no matter when moderate or high and low DO concentration. When this system was operated under the most efficient condition: DO=2.0(aeration)/ 0.4(non-aeration) mg/L, the bacterial richness values were the highest. Under long aeration/non-aeration ratio of 3h: 5h or 5h: 3h, microbial community structure of biofilm was similar with activated sludge. Aerobic and anaerobic bacterium could survive both in activated sludge and biofilm. pH =8.0 was the most efficiency pH condition. The bacterial richness value of biofilm at this time was the highest while the similarity between biofilm and activated sludge was the lowest. However, when pH increased to 9.0, both the microbial community structure and the activities of fuctional baterium were affected. And when pH was 6.0, which has exceeded the physiological range of AOB, NOB and ANAMMOX, the microorganism species sharply decreased.Aeration/non-aeration ratio, DO as well as pH also had the influnence on the populations of fuctional bacterium. High dissolved oxygen was beneficial to AOB and NOB. The quantity of both AOB and NOB were higher in activated sludge than biofilm samples. High DO had the directly influence on ANAMMOX population while low DO also had the inhibitory effect of ANAMMOX activity for the lack of NO3- and NO2- in system. Under the condition of aeration/non-aeration ratio 5h: 3h, DO could transferred into the inner part of biofilm that support a suitable environment for aerabic bacterium. But the effection of ANAMMOX population was not significant. Acid condition of pH 6.0, AOB NOB as well as ANAMMOX populations all dropped sharply while pH 8.0 came to the peak. Because AOB would be instricted by FA, which would be of high concentration under alkaline condition, when pH=9.0 AOB population decreased. The subsequent bacterium such as NOB and ANAMMOX also were influncened indirectly.One Nitroso-bacteria named N1(GenBank registered number: EU647556) was isolated from the SBBR one-step completely nitrogen removal process, and was identified as Nitrosomonas sp. The characteristics of N1 were studied. Results showed that the optimal temperature and pH of N1 were 8.0 and 30℃respectively and sufficient dissolved oxygen was demanded. In addition, the strain was ammonium-tolerant and had no restraint effect in the range of concentration of 80～800mg/L. By using the specific PCR primers and T-A cloning, two species of AOB, 1 species of NOB and 11 species of ANAMMOX were detected in the SBBR one-step completely nitrogen removal process. One of the AOBs dominated at this reactor belonged to the family of Nitrosomonas for the similarity of 98% while another one was almost the same with an uncultured one. The NOB showed close relative to Nitrospira(percent identity 100%). ANAMMOX in this system belonged to Candidatus Kuenenia stuttgartiensis and Candidatus Brocadia fulgida according to the sequence which had a higher percent identity of 97~99%.The activities of nitrosification and anaerobic ammonium oxidation of both activated sludge and biofilm also were studied. Results showed that the nitrosification rate of activated sludge was 2.89 times than biofilm. AOB was the dominate bacteria in activated sludge. However the anaerobic ammonium oxidation rate showed the opposite result. Biofilm was the main part which responsible for anaerobic ammonium oxidation for its 2.44 times reaction rate than activated sludge. ANAMMOX was the dominate bacteria in biofilm.The nitrosification of suspended activated sludge of SBBR one-step completely nitrogen removal process could be defined as the first order reaction. NH4+ began to inhibit nitrosification at the concentration of 560 mg/L. DO=2.0 mg/L and T=30℃were the optimum reaction condition. Meanwhile, the anaerobic ammonium oxidation of biofilm could also be judged as the first order reaction. Haldane model was applied to do non-linear fitting for modelling the relationship between ammonium concentration and the reaction rate. Simulation results showed that the maximum reaction rate in theory was about 0.382 mgN/mgVSS·d while the ammonium concentration at this time was 251.59 mg/L. Compeared with ammonium concentration, the inhibitory effect of the other substrate of anaerobic ammonium oxidation NO2- was more pronounced. The reaction rate dropped rapidly when nitrite concentration was above 70 mg/L. ANAMMOX may lose its activity under the condition of DO=0.1mg/L continous aeration. When pH belonged to 7.0 to 9.0, Antoniou model was suitable for describing the correlation of pH and reaction rate. The best pH in theory was 8.08.