Performances Of Low-strength Wastewater Treatment Based On The AOA-SNDPR Process

In recent years,with the rapid development of China’s economy and society,more and more nitrogen and phosphorus containing sewage enters the natural water,resulting in black and smelly water body,eutrophication and other water environment problems.The traditional biological nitrogen and phosphorus removal technology has low treatment efficiency and will produce a large amount of excess sludge.The simultaneous nitrification and denitrification phosphorus removal process（AOA-SNDPR）in anaerobic/aerobic/anoxic operation mode combines the advantages of simultaneous nitrification and denitrification（SND）and denitrifying phosphorus removal（DPR）,improves the utilization efficiency of organic matter,reduces the demand for dissolved oxygen（DO）in the system,and provides a new idea for efficient and low consumption treatment of urban sewage.In addition,the intermittent anaerobic,aerobic and anoxic environment provides a good niche for the enrichment and growth of a variety of functional microorganisms,especially a variety of slow-growing microorganisms with internal carbon source transformation and utilization,which provides good conditions for in-situ sludge reduction.At the same time,it also avoids sludge bulking induced by excessive proliferation of filamentous bacteria and maintains good operation stability.In view of this,this study proposes to use batch reactor（SBR）to study the AOA-SNDPR process.It is planned to achieve the effect of efficient simultaneous nitrogen and phosphorus removal and sludge reduction by enriching the functional flora related to nitrogen and phosphorus removal.At the same time,the main influencing factors of strengthening the efficiency of the system are explored,to provide guidance and reference for the research、developmentand application of AOA-SNDPR technology.Firstly,taking the simulated urban sewage as the treatment object and the surplus sludge of the sewage treatment plant as the seed sludge,the start-up and subsequent long-term stable operation of the AOA-SNDPR system for 109 days were carried out in the SBR reactor.The effects of nitrogen and phosphorus removal,typical weekly decontamination process,sludge characteristics and changes of microbial community structure during the start-up of the system were explored.The results show that the effluent of the reactor is relatively stable after 15 days of operation.After successful startup,the average concentrations of ammonia nitrogen（NH₄⁺-N）,nitrite nitrogen（NO₂^--N）,nitrate nitrogen（NO₃^--N）,total phosphorus（TP）and chemical oxygen demand（COD）in the effluent of the system can stably meet the class a discharge standard of pollutant discharge standard for urban sewage treatment plants（GB18918-2002）.The pollutant removal results in the typical cycle show that part of COD is transformed and stored as an internal carbon Source in the anaerobic section to supply endogenous nitrogen and phosphorus removal in the aerobic section and anoxic section.Snd in the aerobic section is the main way to remove total inorganic nitrogen（TIN）,anaerobic phosphorus release and aerobic phosphorus absorption are the main ways to remove TP,and denitrifying phosphorus removal also contributes to the phosphorus removal process.Under the condition of no sludge discharge,the sludge concentration（MLSS）of the reactor increased from 3.5g/l of inoculated sludge to 6.4g/L,and the sludge yield（yobs）showed an obvious two-stage rate decreasing mode during operation,and finally stabilized at 0.017g MLSS/g cod.SVI gradually decreased during startup.The sludge activity in the system is very high,and the specific oxygen consumption rate（SOUR）is maintained at 33.14-56.26mg O₂/（g MLVSS·h）;In addition,during the start-up process,the extracellular polymer（EPS）of sludge increased from 53.32 to 103.24mg/g MLVSS,and the PN/PS ratio was stable at about 4.The results of high-throughput sequencing showed that the start-up of AOA-SNDPR process improved the population diversity and abundance of microorganisms,but the diversity decreased in the subsequent long-term operation;Proteobacteria was always the flora with the most phyla level;Gammaproteobacteria was always the flora with the highest level of class;The dominant flora at the genus level ranged from Hydrogenophaga at the time of inoculation to Norank＿f＿＿Saprospiraceae in the middle stage and later Candidatus＿Competibacter.Ammonia oxidizing bacteria（AOB）such as Nitrospirota were increasingly enriched.In order to improve the effect of sewage treatment and sludge reduction,three different initial sludge concentrations of 2.6g/l,3.5g/l and 4.5g/l were set for 51 days.The results show that the AOA-SNDPR system can remove C,N and P under different initial sludge concentrations,and increasing the sludge concentration can strengthen the denitrification effect of the system.When the initial sludge concentration is set at 3.5g/l,the system shows a stronger denitrification effect.The initial sludge concentration is about 2.6g/l,which is more conducive to reduce yobs and realize sludge reduction;And lower initial sludge concentration can obtain lower SVI and higher Source.With the increase of sludge concentration,the contents of PS and EPS showed a decreasing trend.The results of high-throughput sequencing showed that the system with the highest initial concentration showed higher species abundance and diversity.At the phylum level,patescibacteria and elusmicrobiota showed great differences at different initial sludge concentrations;Parcubacteria was significantly different in different samples at the class level;At class level,Parcubacteria were significantly different.The content of Norank＿f＿＿norank＿o＿＿n VP-88 at the general level increased significantly and showed differences in different samples after operation with varying sludge concentration.In order to further enhance the efficiency of nitrogen removal.Five different aeration periods of 90,75,60,45 and 30 min were set up for a period of 63 days.The results show that under the aeration intensity of 200mg/L of the AOA-SNDPR system,the five aeration duration settings can meet the COD removal requirements of the system.The aeration duration of 90min,75min and 60min will lead to excessive do in the subsequent anoxic section and reduce the denitrification effect.The aeration duration of 30min and 45min will lead to incomplete nitrification,and 30min will seriously affect the removal of TP.There was no correlation between aeration duration and sludge yield;The SVI of sludge was stable at about 77 m L/g under five aeration duration in two stages,and the change of aeration duration did not bring significant change of EPS content.The results of high-throughput sequencing showed that the species abundance and diversity decreased after the regulation of aeration time.At the level of phylum,the content of Patescibacteria has increased significantly under the length of 75 min aeration,and at the level of class,it is also Parcubacteria,which has obvious differences in different samples;the relative abundance of Candidatus＿competibacter increased significantly compared with that of seed mud.