Study On Operation And Mechanism Of High Efficiency Denitrifying Phosphorus Removal Reactor

With the development of sewage treatment technology,denitrification and phosphorus removal technology and sludge bulkinghave received increasing attention.How to increase the efficiency of denitrifying phosphorus removal and control the bulking of activated sludge have become the top priorities in wastewater treatment research.Therefore,in this study,two laboratory-built denitrifying phosphorus removal reactors wereset up based on the SBR reactor,effects of changes in the operating mode on nitrogen and phosphorus removal and sludge characteristics were studied.The innovative research results are as follows:?1?Two sets of laboratory-scale denitrifying phosphorus removal reactors were constructed.Aerobic-anoxic?OA?and anaerobic-aerobic-anoxic?AOA?modes were used to study the two reactors.And the effiency of reactors were observed under low,medium and high loads.The results showed that there was no significant difference in the removal rate ofNH₄⁺-N between AOA and OA under different loads,which reached 97.4 and 98.5%,respectively.However,the removal rate of P and total nitrogen in AOA reactor was significantly higher than that of the OA under high load conditions.In the AOA reactor,while the concentration of N and P in influent are 80 mg/L and 40 mg/L,the removal rates of total nitrogen and P reached 82.5%and 92.3%,respectively,which were 1.2 times and 1.4 times the removal rates in the OA reactor under the same condition.?2?The effects of AOA and OA modes on sludge characteristics under high-load and long-term operation conditions were studied.It is worth noting that after long-term operation under high load condition,severe sludge bulking occurs in the OA reactor,while sludge in the AOA reactor still maintains high sedimentation efficiency.After 110 days of high-load continuous operation,the average sludge SV₃₀and SVI average values in the AOA reactor were 22.95%and 38.9,respectively,while the average SV30and SVI values in the OA reactor reached 79.2%and 273.2.This result indicates that the sludge in the OA reactor has undergone severe bulking.The sludge particles in the reactor observed by the microscopy and electron microscopy showed that the shape of the sludge in the AOA reactor was regular,with large particles,large quantities,and dense structure.The sludge particles in the OA reactor were irregular in shape and dispersed,and they are small,little,and the structure is loose.In the bulking phase,the removal efficiency of NH₄⁺-N by the two reactors is not affected.The average removal rate of NH₄⁺-N reaches98.6%,but the removal of P,COD,and N are significantly affected.The removal efficiencies of total phosphorus in AOA and OA reactors were 90.1%and 70.4%,respectively.And the removal efficiencies of COD reached 92.5%and 83.32%,respectively.The average removal efficiencies of total nitrogen were83.84%and 69.90%,respectively.?3?The effect of changes in operating mode on the functional microbial community of denitrifying phosphorus removal organisms was studied.In order to further understand the relationship between various microbial communities and the performance of two denitrifying phosphorus removal reactors under different loads,high-throughput sequencing technology was used to analyze the bacterial community structure under various load conditions in AOA and OA.The results showed that the relative abundance of Rhodocyclaceae at the genus level in the AOA and OA reactors was 40.45%and 47.89%higher than that of the seed sludge under medium load conditions,respectively,and it was similar toseed sludge?about 25%?under low load and high load conditions.At the genera level,the dominant microorganisms in the sludge under different loading conditions are Thauera,Zoogloea,Dechloromonas,Pseudomonas,Candidatus Accumulibacter and so on.The relative abundance of Candidatus Accumulibacter,a typical denitrifying phosphate-accumulating bacterium,was 0.70%,4.89%,2.16%and0.40%,1.47%,and 1.65%in AOA and OA reactors under different loads,which were much higher than that in seed sludge.The relative abundance of polyphosphate-associated functional microbes?Candidatus Accumulibacter,Dechloromonas,Acinetobacter?was 8.37%,11.26%,10.72%and 6.44%,5.18%,and8.39%,respectively.This results indicates that denitrifying phosphorus-accumulating microorganisms were riched in the reactorobviously.In addition,we also analyzed the microbial community structure in the OA reactor sludge bulking stage while the two reactors were run under long-term and high-load conditions.The results showed that,at this phase,the genera of Candidatus Accumulibacter,a typical denitrifying phosphate-accumulating bacterium,dominated the genera and its relative abundance was 15.0%in the AOA reactor.The main advantage of the OA reactor is the Thauera genus,which has a relative abundance of 43.4%and the Thauera is thethe main cause of sludge bulking.The relative abundances of the GAO?Candidatus Contendobacter and Candidatus Competibacter?in AOA reached 5.37%and 3.63%,respectively;at the level of species,the abundance of GAO?Candidatus Contendobacter odensis?was highest in the AOA reactor.5.37%;the relative abundance of Dechloromonasdenitrificans in AOA was1.41%;the relative abundances of Candidatus Accumulibactersp.BA-92 and Candidatus Accumulibacter sp.BA-93 which were the denitrifying phosphates removalorganisms were 3.74%and 2.71%,much higher than their 0.10%and 0.098%in seed sludge and their 0.048%and 0.028%in OA.The strain Thaurea phenylacetica,which can cause sludge swelling,has a relative abundance of 8.84%in OA,which is much higher than 0.61%in the AOA reactor and 0.44%in the seed sludge.?4?The effects of changes in operating mode on the functional genes of denitrifying phosphorus removaling?NirK,NirS,NarG,Acc-?C,Acc-?D,Acc-?F?were studied.The results showed that the gene abundances of Acc-?C,Acc-?D,and Acc-16S rRNA were mostly above 1 in the AOA,and the enrichment multiples compared to the original sludge were more than one,which were higher than their enrichment multiple in OA.Especially under the medium load condition,the enrichment multiple of Acc-?C in AOA is as high as 80.Therefore,the operating conditions of the AOA reactor can more effectively remove the pollutants in the influentand enrich the denitrifying polyphosphorus-related functional microbial genes.Under long-term and high-load condition and sludge bulking stage,the numbers of the denitrification genes NirS,NarG and NirK in the AOA reactor were 3.43×10⁸ copies/g dry sludge,1.9×10⁷ copies/g dry sludge and 5.1×10⁷ copies/g dry sludge respectively.During the sludge bulking phase,the bacterial 16S rRNA gene copy number in the AOA reactor was 5.02×10⁸ copies/g dry sludge,which was an order of magnitude higher than that of the seed sludge and OA reactor;and the number of 16S gene of the typical polyphosphateaccumulating organisms“Candidatus Accumulibacter”was 1.2×108 copies/g dry sludge,which was also an order of magnitude higher than the gene copy number of this strain in the OA reactor.The enrichment multiples of polyphosphorus-related genes Acc-?C ,Acc-16S rRNA and Acc-?D in AOA reactors were 133.90fold,12.32fold and 7.29fold,compared to the sludge,respectively.And the enrichmentmultiples of the denitrification genes NirS and NirK were 1.88 and 1.91,respectively,while the enrichment multiple of NarG gene was only 0.75 compared to the seed sludge;Denitrification and polyphosphorus-related gene abundances were reduced in OA reactors,and the enrichment multiples of NirK,NirS,and NarG genes were 0.23,0.26,and 0.11,respectively.The gene Acc-?D,Acc-?F,and Acc-16S rRNAenrichment multiples were 0.077,0.019,and 0.433,respectively.?5?Isolation and identification of denitrifying phosphorus-accumulating bacteria.56 denitrifying strains were isolated from the denitrifying dephosphorization reactor constructed in the laboratory,of which15 strains were established to have the ability to remove phosphorus simultaneously.There were 3 strains which have more than 40%phosphorus removal efficiency.The highest phosphorus removal efficiency was49.6%for Kluyveracry ocrescens,41.6%for Comamonas testosteroni,and 41.2%for Pantoea agglomerans.