Effect Of Seed Sludge On The Start-up And Performance Of Autotrophic Nitrogen Removal Granular Sludge Reactors

The one-stage partial nitritation and anammox?PN/A?process based on anaerobic ammonium oxidation is one of the most cost-effective new autotrophic nitrogen removal processes.Compared with the traditional nitrification-denitrification process,PN/A process has the advantages of low energy consumption,no carbon source required,saving infrastructure cost and so on.But it still has some shortcomings such us the unstable startup process,long startup time and low sludge removal load.The granular sludge with high density,good settling property,excellent biological retention ability and strong impact load capacity,has been more and more used in completely autotrophic nitrogen removal process.This thesis systematically studied the effects of different sludge inoculation on the rapid start-up of one-stage PN/A granular sludge process,and the synergistic effect of functional bacteria in autotrophic nitrogen removal granular sludge was further explored.The main research contents and results of this paper include the following 3 aspects:1.Continuous flow and sequencing batch modes were used in stages to operate the completely mixed flow reactor inoculated with nitrosation granular sludges,in order to start up a partial nitritation and anammox?PN/A?process.The variations of reactor performance,sludge morphology and activity,and microbial community structure were investigated in detail.Results showed that sequencing batch operation could promote the increases in both sludge concentration and reaction activity at high influent ammonium loading rate and high dissolved oxygen level,on basis of an appropriate nitrogen substrate ratio obtained in the initial continuous flow stage.Then a superior total nitrogen removal rate of 1.75 kg·?m³·d?^-1was achieved in the subsequent continuous flow mode.During the operation period,the compactness and settling property of granules were improved obviously.And Miseq high-throughput pyrosequencing analysis revealed that PN/A granular sludge showed a relative higher microbial diversity.Corresponding to the specific nitrogen removal rate of 0.24 g·?gVSS·d?^-1,the abundance ratio between aerobic and anaerobic ammonium oxidation bacteria was around 3 to 1,in terms of gene Nitrosomonas and Candidatus Kuenenia,respectively.In addition,few oligotrophic nitrite oxidation bacteria in the granules would not affect the efficiency of PN/A process significantly.2.In order to obtain experimental evidences for optimizing completely autotrophic nitrogen removal process based on granules,the effects of dissolved oxygen?DO?concentration,temperature?t?,initial ammonium?NH₄⁺-N?concentration and solution pH conditions on synergy between aerobic and anaerobic ammonium-oxidizing bacteria?AOB and AMX?were investigated with single factor batch experiment,while the analysis of microbial community structure within them was conducted using MiSeq high-throughput pyrosequencing.Results revealed that AOB?genus Nitrosomonas?and AMX?genus Candidatus Kuenenia?dominated in the granules,representing the relative abundances of 32.9%and 9.8%,respectively.For the granules,the highest specific nitrogen removal rate of q?TN?=?17.7±1.0?mg·?g·h?^-1 was obtained at DO concentration of 2 mg·L^-1,while the initial NH₄⁺-N concentration was set at 100 mg·L^-1.And a lower DO level resulted in the partial nitritation became the rate-limiting step of process,otherwise,it would be the anammox reaction instead.According to free energy of reactions,the activity of AMX was more sensitive to low temperature than that of AOB.When the reaction temperature was lower than 30?,a nitrite accumulation would be observed in bulk liquid,with the significant decrease of q?TN?for the granules.Under same oxygen supply conditions,the initial NH₄⁺-N concentration lower than 100 mg·L^-1would inhibit the activity of AMX partly.However,with the initial NH₄⁺-N concentration over 150 mg·L^-1,either oxygen-limiting or high free ammonia concentration would lead to the dramatic decrease of q?TN?.In addition,the effective synergy of two types of ammonium oxidizers in granules was always achieved at solution pH in range of 7.0⁸.5.3.One-stage autotrophic nitrogen removal process was started up in three identical CSTR?continuous stirred tank reactor?reactors feed with synthetic wastewater with NH₄⁺-N of 200 mg·L^-1,which were inoculated with completely autotrophic nitrogen removal granule sludge and nitrosated granular sludge.The volume ratio of mixed sludge was 3:1,1:1,1:3 respectively.The results indicated that R1 and R2 were started-up successfully on day 49 with nitrogen removal rate of 2.1 kg·?m³·d?^-1and 1.8 kg·?m³·d?^-1,the sludge in the stable operation of the reactors were reddish brown.While,R3 was started up by 92 days with NRR of 2.5 kg·?m³·d?^-1,which was longer than R1 and R2 for43 d,and a small part of the activated sludge remained yellowish.The particle size of the granular sludge in the three reactors was maintained between 0.9 and 1.0 mm.After the reactors were successfully started,the removal rate of total nitrogen in the sludge were0.32 g·?gVSS·d?^-1,0.34 g·?gVSS·d?^-1,0.38 g·?gVSS·d?^-1,respectively.The nitrosated granular sludge in the inoculation sludge is beneficial to the improvement of performance in the autotrophic nitrogen removal granular sludge systems.These two granular sludges inoculated with an equal volume to start up the partial nitritation and anammox granular sludge process has the dual advantages of saving economy and time.