Study On The Cultivation Of Aerobic Granular Sludge With Low-carbon Municipal Sewage And The Removal Performance Of Nitrogen And Phosphorus

The municipal sewage in China generally shows the characteristics of low COD and low carbon-to-nitrogen ratio.It is difficult for the conventional sewage treatment process to achieve a good simultaneous nitrogen and phosphorus removal.Technology has become the focus of research in this field.In this study,the simulated low COD concentration municipal sewage was used as the substrate to systematically study the aerobic granular sludge cultivation and its ability to remove nitrogen and phosphorus in A/O/A SBR.The main contents are as follows:(1)Aerobic granular sludge rapid cultivation and stability control.In the SBR reactor,municipal wastewater with low concentration of COD(300 mg/L)was artificially prepared as the influent substrate,and anaerobic/aerobic/anoxic(A/O/A,85/90/40 min)operating mode to cultivate aerobic granular sludge.During the organic load from 0.82 kgCOD/(m3·d)to 1.2 kgCOD/(m3·d)and the precipitation time from 15 min to 3 min,mature aerobic granules were formed on 75 days sludge.It forms a state in which yellow and white granular sludge coexist.Through the bottom sludge discharge method,the particle size range of the granular sludge is controlled at 2-3 mm,the system can maintain high nitrogen and phosphorus removal performance and long-term stable operation.(2)Comparison of physical and chemical properties of yellow and white granular sludge.A large number of short rod-shaped bacteria and spherical bacteria are distributed on the surface of the yellow and white granular sludge,and contain more pores.The white granular sludge has a large particle size(about 3.2 mm),a smooth surface,and a spherical or ellipsoid appearance,but the internal structure is loose;the yellow granular sludge has a small particle size(about 2.1 mm)and a rough surface,The appearance is irregular,but the internal structure is dense.The physical and chemical properties of yellow and white granular sludge are obviously different:compared with yellow granular sludge,the moisture content of white granular sludge is slightly higher(water content is 94.23%(yellow),97.08%(white)),the specific gravity is slightly lower(The specific gravity is 1.042 g/cm3(yellow)and 1.031 g/cm3(white)respectively),the EPS content and PN/PS value are higher(EPS content:8.88 mg/g MLSS(yellow)and 18.48 mg/g MLSS(white);PN/PS value:0.292(yellow)and 0.633(white)).(3)Analysis of pollutant removal performance and mechanism.After the system runs stably,the average effluent COD,TN and TP concentrations are 16,13.45 and 0.21 mg/L,respectively.And the removal rates are 94.7%,66.4%and 97.4%,respectively.It has good anaerobic phosphorus release capacity and excessive aerobic phosphorus absorption capacity.Simultaneous nitrification and denitrification occurs in the aerobic section(SND rate is 47.5%).The effect of nitrogen and phosphorus removal and the comprehensive utilization efficiency of carbon source are discussed.(4)Explore ways to optimize the performance of nitrogen and phosphorus removal.Extending the post-anoxic duration to 165 min(cycle 6 h)and 270 min(cycle 8 h),the TN removal rate increased to 86.3%,nearly 100%(below the detection line);the effluent TP concentration was lower than detection limit,removal rate increased to nearly 100%.Therefore,it is possible to achieve an efficient nitrogen and phosphorus removal effect by extending the post-anoxic duration.(5)Comparison of microbial community structure.MiSeq high-throughput sequencing technology was used to analyze and compare the microbial community structure of inoculated floc sludge and yellow and white granular sludge.The results showed that the microbial diversity and abundance decreased in the process of sludge granulation,and the microbial diversity of yellow granular sludge was much higher than that of white granular sludge.The main communities in the yellow and white granular sludge are related bacterial groups that can secrete a large amount of EPS and have the effect of nitrogen and phosphorus removal.The predominant phylum in yellow and white granular sludge is Proteobacteria(accounting for 68.93%(yellow)and 82.98%(white),respectively);the predominant dominant is Gammaproteobacteria(yellow,45.83%of the total),Betaproteobacteria(white,64.38%);at the genus level,the white granular sludge is mainly Candidatus_Accumulibacter and Dechloromonas(56.72%of the total),has good aerobic phosphorus removal and denitrifying phosphorus removal capacity,and its denitrifying phosphorus removal performance and phosphorus removal performance are superior to yellow granular sludge.DPAOs/PAOs are 25.1%(yellow)and 70.9%(white)in yellow and white granular sludge,respectively;yellow granular sludge is mainly Candidatus_Competibacter(35.75%),with good endogenous denitrification capacity.(6)Explore the formation mechanism of yellow and white granular sludge from the perspective of microbial community.In this study,the low COD concentration municipal sewage substrate and bottom water intake method used in A/O/A SBR have improved the competitiveness of PAOs in various bacterial groups.The predominant bacteria in white granular sludge are PAOs.The granular sludge formed by rapid accumulation and overgrowth of PAOs forms larger particles in a short period of time.The shape is more loose and have better light transmission properties,so they appear white.The dominant bacteria in yellow granular sludge are GAOs,which are growth-limited but can secrete a large amount of viscous EPS.Under the action of higher hydraulic shear force,GAOs and various bacterial groups slowly aggregate to form granular sludge.The shape is more compact,and light transmission performance is poor,so it appears yellow.