Ultrasonic Treatment Of Activated Sludge Accelerates Nitrification And Denitrification Rates

In the process of purifying wastewater containing nitrogen,the ability of degradation of nitrogen pollutants by activated sludge usually increases with the increase of sludge biomass,but high sludge concentration will lead to many problems,for example,dissolved oxygen is reduced,sludge bulking and mass transfer efficiency is reduced,so high concentration sludge process has not been widely developed and applied in engineering.Ultrasonic treatment is an environment-friendly physical and chemical technology.Low intensity ultrasonic treatment can change the microbial structure,increase the enzyme activity and enrich the dominant bacteria.However,high intensity ultrasonic treatment can cause irreversible damage to the sludge,resulting in the death of the sludge and the release of intracellular substances.In this experiment,low-intensity ultrasound was applied to the nitrification process of high-concentration sludge to study the effects of low-intensity ultrasound on the particle size,specific surface area,specific oxygen consumption rate,sedimentation performance and adsorption performance of the nitrified sludge,the effect of low intensity ultrasound on the nitrification rate of high concentration nitrifying sludge was studied.In addition,this experiment applies high intensity ultrasound to the treatment of denitrifying sludge to study the organic carbon source released by the sludge under the high intensity ultrasound,a kinetic model was established to study the synergetic mechanism of degradation of nitrate nitrogen by the combination of ultrasonic treatment sludge and untreated sludge.The main conclusions of this study are as follows:(1)Ultrasonic treatment of nitrified sludge will reduce the particle size and increase the specific surface area of the particles.(2)The specific oxygen consumption rate of high biomass nitrifying sludge is lower than the normal operation requirement,the settling rate of sludge is slower,and the adsorption capacity of sludge to ammonia nitrogen is higher than that of low biomass sludge.Low intensity ultrasonic treatment of high biomass nitrified sludge can increase the specific oxygen consumption rate,improve the sludge sedimentation performance and further enhance the adsorption capacity of sludge.(3)Ultrasonic intensity(including ultrasonic energy density and ultrasonic time)can accelerate the degradation of ammonium nitrogen by nitrification sludge and nitrate nitrogen by denitrification sludge in a certain range,but the rate decreases when the ultrasonic intensity is too high.(4)When the sludge concentration was low,the nitrification rate increased with the increase of the sludge concentration,but when the sludge concentration was too high,the growth trend of nitrification rate slowed down or even stopped increasing;However,low intensity ultrasonic treatment of nitrification sludge can make the nitrification rate always increase with the increase of sludge concentration.(5)The floc of nitrification sludge was dispersed after low intensity ultrasonic treatment,but the sludge cell activity did not significantly decrease.Low intensity ultrasonic crushing treatment can reduce the diversity of microbial community in nitrification sludge,but increase the specificity of microbial degradation to specific pollutants.Ultrasonic treatment can increase the relative abundance of nitrifying bacteria,so that the nitrification rate presents an upward trend.(6)In the denitrification process between ultrasonic treatment and untreated mixed sludge,the ultrasonic treatment sludge provides bioavailable carbon source,while the untreated sludge provides bioactive microorganisms,forming a synergistic acceleration effect.When C/N=3,the ratio of treated and untreated sludge in the system remained 1:3,and the denitrification rate of sludge increased the most,reaching 200%.When C/N=4,the ratio of treated and untreated sludge in the system remained 1:1,and the denitrification rate increased the most,reaching 65%.When C/N ratio is 3 and 4,the denitrification rate of the mixed sludge can be expressed by the first-order kinetics model as r1=0.231Xu+0.46(?)+0.654Xt and r2=0.431Xu+0.62(?)+0.463Xt.(7)After the denitrifying sludge is treated by high-intensity ultrasonic treatment,the number of microorganisms in the denitrifying sludge will be reduced by high-intensity ultrasonic treatment,but the relative abundance of bacteria with denitrifying function in the sludge will increase,thus improving the denitrification capacity of the sludge.In addition,high-intensity ultrasonic treatment can break up the denitrifying sludge floc and make the sludge cells crack and release the organic matter,but this process will destroy the denitrifying bacteria and reduce the cell activity.