The Study On The Performance And The Charicteristics Of Microbial Communities In A Single-stage Partial Nitritation-anammox System Combined With Flocs And Granules

Single-stage Partial Nitrification-Anammox(PN-A)is a novel biological nitrogen removal process with no additional organic carbon,lower aeration comsuption and less green-house gas emission.However,the development of this process has been hindered,due to the long start-up period and instability of operation recently.The performance of this process could be improved efficiently by adjusting the morphology of sludge.Granular sludge(size more than 200?m)is the desired sludge type for its good settleability and varied microbial structure,and yet the floc sludge(size less than 200?m)plays a vital role in the nitrite accumulation under in practical operation.At present,some researches have been carried on the characteristics of different sludge type in hybrid reactor combined with flocs and granules.But limited studies focus on the control strategies and the variation of characteristics of different sludge type when the proportion of different sludge changes.In this study,a hybrid PN-A system with different level of flocs was established successfully by incoluted mature compelected autotrophic nitrogen removal sludge and anammox sludge and achieved a good nitrogen removal performance.Highthroughput sequencing technology was applied to detect the microbial communities to further investigate the mechanism of sludge ratios affecting the activities and distribution of functional communities.Finally,a model was set up to predict the abundance variation of functional communities in a hybrid system based on ASM2(Activated sludge model No.2).The model forecast results were vertified by the detection results.The main content of this study were as below:(1)The hybrid PN-A system has operated for 217 d,dividing into high proportion of flocs(the ratio of flocs to granules is 1:2)phase and low proportion of flocs(the ratio of flocs to granules is 1:10)phase.In the first phase,the nitrogen removal efficiency(NRE)was up to 90%and nitrogen removal rate reached 0.31 kgN/m~3/d when DO was turned from 0.12 mg/L to 0.22 mg/L.In the second phase,the nitrate concerntration in effluent was quite high.Taking‘high pH and low DO'strategy,the nitrate oxidizing rate(NOR)dropped from 42.2 mgN/L/h to 27.3 mgN/L/h and NRE was stablitily at around 80%.(2)Batch tests were carried out to measure the nitrogen removal rates of flocs and granules demonstrating that the maximum ammonia depletion rate and maximum nitrite production rate of flocs were up to 20.0 mgN/L/h and 14.2 mgN/L/h,resperctively;whereas that of granules was nearly zero in the first phase and yet the maximum ammonia depletion rate was 10.1 mgN/L/h.Meanwhile nitrogen removal was detected in flocs and granules.In the second phase,the maximum nitrite production rate of flocs was only 4.0 mgN/L/h,whereas the ammonia depletion rate significantly increased from 10.1 mgN/L/h to 22.0 mgN/L/h.In addition,nitrogen removal was detected in granules.In the term of heterotrophic bacteria,the maximum variation of soluble microbial products(SMP)was up to 481.6 mg/L in the first phase,compared to 212.8 mg/L in the other phase.The nitrogen removal ratio contributing by heterotrophic denitrification bacteria(HDB)in phases were 6.1%and 1.0%,resperctively.(3)The OTUs of four samles(62-F,62-G,123-F and 123-G)were detected through high throughput sequencing technology and were 791?6119?3070 and 3366.The result of Shannon index demonstrated that 123-F>123-G>62-G>62-F,indicating the reduction of proportion could contribute to the improvement of diversity of microbial communities.For community structure,Planctomycetes was the dominat phylum in all samples,accounting for 54.31%?45.01%?28.17%and 23.08%.The result of spatial distribution determination suggested that AOB,composed of Nitrosomonas,was mainly enriched in flocs in any phase,and yet sludge ratio increased along with the abundance of AOB in granules increasing.The abundance of NOB was higher in granules in the first phase,but in the second phase,the abundance was higher in flocs.AAOB,composed of Candidatus Kueneni and Candidatus Brocadia,was the dominat community in the first phase,where the abundance of AAOB was more than35%both in flocs and granules.However a drastic decline was observed in the second phase influencing by the adjustment to sludge morphology.In the second phase,the NOB activities of granules declined from 5.80 mgN/h/gVSS to 3.24 mgN/h/gVSS,whereas AAOB activies rised from 3.15 mgN/h/gVSS to 5.64 mgN/h/gVSS along with the decrease of DO and the increase of FA.(4)Based on ASM2,the model to predict the distribution of microbial in a hybrid system was constructed by the kinetic equation of microbial growth.The final results illustrated that when the sludge ratio was 1:2,system facilited the enrichment of AOB in flocs and supported synchronously the growth of AOB and AAOB in granules.When the ratio dropped to 1:10,the abundance of AOB still kept a good growth trend in flocs,wherease AAOB showed a negative competition with NOB.In granules,the growth trend of all the communities had a little difference compared with the phase before.