| Under aerobic conditions and other special conditions,microorganisms spontaneously agglomerate and proliferate,and immobilize themselves to form a kind of particulate biological agglomerates called aerobic granular sludge.Morphologically speaking,aerobic granular sludge has the characteristics of flocculent sludge.It can be suspended in water and has a large contact area with the sewage.Therefore,nutrient and DO transfer rates in the influent water are high.The increase in the material transfer rate can increase the metabolic efficiency of organisms and accelerate the degradation of substrates.It also has the characteristics of the biofilm method,which is rich in microorganism types and it is not easy to lose.And the excess sludge in the reactor can be quickly separated to avoid microbial loss.From the point of view of microbial populations,microbial populations are diverse,numerous in quantity,and have long biological chains,and each microbial interaction in granular sludge is intense.Experts and scholars proved that the aerobic granular sludge technology has the technical features that other existing wastewater biological treatment technologies do not have,but the aerobic granular sludge is not yet reached practical application.In this paper,the continuous-flow network board reactor is designed and operated,rapid cultivation of aerobic granular sludge and stable operation are maintained,and the effect of continuous-flow network board reactor on the process of aerobic granular sludge cultivation is analyzed.The formation mechanism,disintegration cause,countermeasures,and stable operation of aerobic granular sludge were discussed through the analysis of particle sedimentation performance and water treatment effect.In the first part of the experiment,the R1 continuous-flow reactor with network board reactor and the R2 continuous-flow reactor without network board reactor were compared and analyzed to verify the key role of network board reactor in rapid training and stable maintenance.Aerobic granular sludge was found in R1 on the 14 th day,then it became qualified granular sludge on 25 d and operated stably,and qualified aerobic granular sludge was found in R2 on the 30 th day and the quantity is little.During the stable operation stage of R1,the particle diameter is about 2.5 mm,sedimentation rate is 47.8 m/h,MLSS is about 5700 mg/L,SVI is about 21 m L/g,and SV30 is about 12.5%.While During the stable operation stage of R2,the particle diameter is about 1.8 mm,sedimentation rate is 37.0 m/h,MLSS is about 4400 mg/L,SVI is about 40 mL/g,and SV30 is about 18.0%.This result showed that the microorganism content in R1 was more than R2 and the sedimentation ability of mud particles was superior to R2.The removal rates of COD,TN,NH4+-N and TP effluent indicators in R1 were stable at 87.96%,81.25%,86.61%,and 77%,it was compared with R2 water treatment capacity,the R1 removal rate was higher and the effluent quality was better.In R2,the disintegration of particles occurred on 43 rd day,while R1 was stable for 50 th day.It is proved that the continuous-flow network board reactor has a key role and application value in the rapid formation and maintenance of stability of aerobic granular sludge.The analysis of the disintegration expansion of aerobic granular sludge was due to the excessive proliferation of filamentous bacteria,filamentous bacteria has a large specific surface area and a fast transfer performance,as the device continued to operate,the sludge load in the reaction zone and the consumption of nutrients such as N and P were depleted,then filamentous bacteria became the dominant species,and the amount of nutrients absorbed was much greater than other species,in this condition,filamentous bacteria can grow more rapidly and produce more filamentous bacteria.Against to the the phenomenon of particles disintegration which was due to excessive number of dominant bacteria under certain conditions in pre-experimental experiment,the size parameters of the continuous-flow network board reactor were optimized,and the cross-sectional area of four water corridors in the front-end pre-reaction zone was reduced.Also adjusted the operating parameters to increase the surface gas velocity to 0.025m/s,and increased the influent flow to 100L/h when the device was initially started,and the organic load was corresponding increased to 4kgCOD/(m3·d),then on 25 th day in order to increase the content of nutrients such as N,P in the reaction zone,a constant flow pump was added to reaction zone for inflow,the inflow is 25L/h,and the total inflow was increased to 120L/h at the same time,the organic load was corresponding increased to 5.5kgCOD/(m3·d),After 40 th day,the influent flow was continuously controlled at 140L/h,and the influent organic load was 6.5kgCOD/(m3·d).After optimizing the reaction device and operating parameters,particles with small particle size appeared in the main reaction zone on the 12 th day,the particle size reached maximum on 20 th day,when the particle was fully mature,the average particle diameter increased to 3.0 mm,then holding device continued to run until the 70 th day actively stopped and the particles remained stable during this period.The sedimentation rate of mature particles was 48~52 m/h,SVI was maintained at 17.5~19.5 mL/g,SV30 was maintained at 10.0%~12.0%;the average removal rate of COD was 90%,and the average removal rate of TN was 84%,the average removal rate of TP was 75%.In the process of using continuous-flow network board reactor to cultivate aerobic granular sludge rapidly,the "crystal nucleus hypothesis" and "microbe self-condensation hypothesis" were the main supporting theories of the experiment.The domestic sewage and the inoculum sludge used in the experiment all contain granular materials with small particle size,during the formation of aerobic granular sludge,the particles needed to collide with each other to aggregate and increase the maturity of the particles,these particles are used as the core in this process.In addition,the microorganisms are attached to the stencil reactor then being broken into tiny bio-film fragments under the action of shear forces after forming into bio-films,these fragments entered the main reaction zone and became the core of the aerobic granules afterwards.Microorganism will secrete EPS which is viscous on its surface when the external environmental conditions which exist in changed and under the condition of high hydraulic shear force,under the action of rising water flow,airflow,gravity,shear force,and reaction device walls,finally the aerobic granular sludge with close structure,superior settling performance and high mass transfer efficiency was generated due to the collisions and agglomerations of microorganisms. |
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