Characteristic Of Anammox Microorganismunder Different Culture Modes

Anaerobic ammonia oxidation?Anammox?is gradually becoming the focus of the wastewater nitrogen removal process because of its prominent specialty such as without adding organic carbon source,low oxygen consumption and saving excess sludge yield,as well high nitrogen removal efficiency.However,Anammox bacteria is slow growing and sensitive to environment,which limits the further application of Anammox.Therefore,how to rapidly enrich Anammox sludge with sufficient biomass and good biological activity is the key to ensure the efficient and stable operation of Anammox reactor.Substrate concentration plays a key role in enrichment of Anammox bacteria.In this paper,the effects of substrate exposure level on the operational efficiency and microbial characteristics of Anammox were investigated.Using two continuous flowreactors,by means of controlling the pH,DO,and temperature being 7.8⁸.2,less than 0.2 mg/L,and 35³7?of the reaction systems respectively,and fixing HRT with 0.5 d,the reactors were operated 102 d steadily.In the process of gradually developing nitrogen load,by investigating changes of the Anammox sludge concentration,the total copies number of Anammox functional genes,and the anaerobic ammonia oxidation activity,as well the microbial diversity under high substrate exposure levels culture methods?exposure concentration of NH₄⁺-N and NO₂^--N are between 40 and 60 mg/L?and low substrate exposure levels culture methods?exposure concentration of NH₄⁺-N and NO₂^--N are between 0 and 20mg/L?,influence of different culture methods were explored on the Anammox biomass,activity,and microbial community,as well the nitrogen removal efficiency of the reactors.The main research results were as follows:?1?Anammox sludge with good apparent activity could be obtained in both high and low substrate exposure culture methods.The sludge had a typical brick red color,and its particle size was between 1¹.5 mm,and the main shape of the granular sludge was spherical or ellipsoid.The apparent morphology of Anammox sludge cultured with different culture mode showed little difference;?2?Under the culture mode with high substrate exposure level,sludge concentration and total gene copy numbers of Anammox reached 1805 mg VSS/L and4.81×10¹² copies respectively.Its biomass was 1.2¹.4 times of the low substrate exposure culture mode(1506 mg VSS/L and 3.39×10¹² copies).Therefore,the culture mode with high substrate exposure level was more conducive to the rapid enrichment of Anammox sludge;?3?The activity of Anammox sludge is related to its particle size and EPS content.When the particle size of sludge is less than 1.5 mm,the activity of Anammox microorganisms increased with the increase of particle size.Within a certain range,the higher the EPS content,the stronger the activity of the sludge.SAA of Anammox sludge was increased from 0.05 g N/?gVSS·d?at the time of inoculation to 0.24 g N/?gVSS·d?and 0.27 g N/?gVSS·d?under the two culture modes of high and low substrate exposure levels.The Anammox sludge activity in the environment with low substrate exposure level was 22.7% higher than that in the environment with high substrate exposure level.The culture mode with low substrate exposure level was more conducive to the enrichment of Anammox sludge with stronger biological activity;?4?The culture mode with different substrate exposure levels did not show the decisive influence on the phyla structure distribution of Anammox microorganism.Under different substrate exposure level culture methods,the microorganism mainly included the five most abundant phylums,namely,Chloroflexi,Proteobacteria,Planctomycetes,Bacteroidetes,Chlorobi.The relative abundance of Chloroflexi and Chlorobi decreased by 7.7% and 59.9⁶8.8% respectively.While relative abundance of Proteobacteria and Bacteroidetes increased significantly:the relative abundance of Proteobacteria increased by 35.2³9.9%,and the relative abundance of Bacteroidetes increased by 6.4⁸.35 times.The overall trend of Planctomycetes was stable,and its relative abundance is 15¹6%.?5?The culture mode with different substrate exposure levels did not show the decisive influence on the selection of dominant species of Anammox microorganism.Candidatus Brocadia and Candidatus Jettenia were selected as the functional bacteria of Anammox under different substrate exposure levels.Candidatus Brocadia?3%? was the predominant bacteria,and the percentage of Candidatus Jettenia?0.01%? was very low.?6?Substrate exposure level has an obvious influence on the relative abundance of Candidatus Brocadia which is functional bacteria of Anammox.Under the culture mode with high substrate exposure level,the relative abundance of Candidatus Brocadia was 24.8% higher than the culture mode with low exposure substrate level.?7?The nitrogen removal performance of Anammox reactor was determined by the activity and biomass of Anammox microorganisms retained in the reactor.When the difference of microbial activity was small,the biomass played a key role in the nitrogen removal efficiency of the reactor.The NLR and NRR obtained under the high exposure level culture mode were 0.69 kg N/?m³·d?and 0.41kg N/?m³·d?respectively.It was significantly higher than the low substrate exposure level culture mode?NLR and NRR were 0.41 kg N/?m³·d?and 0.21 kg N/?m³·d?,respectively?,and the high substrate exposure level culture mode was more conducive to the improvement of nitrogen removal performance of Anammox reactor.