Determining The Effects Of Aeration Intensity And Reactor Height To Diameter Ratio On Granule Stability Analysis

Aerobic granular sludge was considered as a leading wastewater technology in next century which has broad development prospects.Aerobic granular sludge feeding with synthetic wastewater was successfully cultivated in a sequencing batch reactor.Aerobic granular sludge has multiple advantages such as a dense physical structure,excellent sedimentation performance,high biomass retention,and high pollutant removal efficiency.However,the long startup time and the loss of granule stability limited the application of this promising biotechnology.How to achieve a rapid sludge granulation and to maintain long-term stable operation is worth exploring.In this study,the effects of different operating conditions(organic load,aeration intensity,settling time,screen)on the granulation were investigated to analyze.It aims to analyze the influence degree of different factors on its granulation and obtain the optimum conditions for sludge granulation,which has guiding significance for real production.The research shows that the influent organic load is positively correlated with the EPS content of the sludge.Increasing the influent load is beneficial to the granulation.However,the granular structure is loose and easily broken under the high load condition(3 kg/COD~3·d);the aeration intensity promotes the formation of dense particles,but inhibits the granulation rate of sludge;the short settling time promotes the discharge of light flocs.But in the initial stage of reactor start-up,too short settling time easily leads to excessive biomass loss.According to the research,low-intensity water inflow(1.5 kg/COD~3·d)is adopted at the initial stage of the reactor and gradually increasing the pressure of selection,sludge loss can be effectively suppressed and the treatment effect can be guaranteed during the startup period.Increasing aeration intensity and height to diameter(H/D)ratios were conventional strategies to enhance granules stability.In this study,hydraulic effects of aeration intensity and H/D ratios were explored basing on bubble behavior analysis.However,results revealed that due to viscous resistance,increasing aeration intensity and H/D ratio had limited effects on enhancing hydraulic shear stress,not to mention the extra operation and construction cost.In conventional reactors,the overgrowth of large granules led to granule breakage and disintegration.Paracoccus sp.and Flavobacterium sp.situated in inner part of granules were exposed due to granule disintegration,and were washed out of the reactor,which resulted in equal Paracoccus sp.and Flavobacterium sp.abundance in effluent flocs and granules.A deflector component was further applied to regulate hydraulic shear stress on large granules under low aeration intensity and H/D ratio.Hydraulic shear stress on large granules was constantly around 3.0 times higher than conventional reactor,resulting in higher percentage of granules within optimal size range 81.95±5.13%.A high abundance of denitrifying bacteria was observed in reactors,which led to high TN removal efficiency of 88.6±3.8%.