Experimental Study On Micro-bubbles Promoted Sludge Degradation And Dehydration Based On Ultrasonic Conditioning

With the increase of sewage treatment plants in China,sludge has also increased year by year.If it is not properly treated,it will cause secondary pollution to the environment,it must be reduced first.Pretreatment can improve the dewatering characteristics of the sludge,so as to achieve the optimal reduction effect.Ultrasonic and micro-bubbleshave the characteristics of high efficiency and environmental friendlinessand attracte more and more attention from scholars at home and abroad.The dewatering characteristics of municipal sludge were studied by ultrasonic.The changes of ultrasonic oxidation properties under different conditions were measured.When ultrasonic are used alone,the conditions that are more favorable for dehydration characteristics are that the ultrasonic time is 120 s,the ultrasonic power is450 W,and the processing capacity is 80 m L.At the same time,the CST of the sludge obviously increased after the ultrasonic effect,and the particle size showed a trend of first decrease and then increase,and reached the lowest point when the ultrasonic time was 120 s and the power was 450 W,respectively.In order to improve the effect of reduction and promote the anaerobic treatment of sludge,an experimental device for sludge treatment with ultrasonic and micro-bubbles in a continuous flow state was built.Micro-bubbles pretreatment and ultrasonic-cooperative micro-bubbles pretreatment experiments were carried out.In the experiment of pretreatment of micro-bubbles,the mechanism of micro-bubbles pretreatment was analyzed by measuring the oxidation of micro-bubbles and the changes of various parameters of sludge after treatment.The UV-spectroscopy method was used to determine the oxidative property,and it was found that the concentration of I₃^-decreased first and then increased.The effect of micro-bubbles on the sludge dewatering characteristics was analyzed through a combination of direct characterization and indirect characterization.The sludge dehydration rate and the moisture content of the sludge cake were basically opposite to each other.Layered tests were performed on the EPS,and it was found that the average surface area particle size and the change trend of the polysaccharide content in the LB-EPS layer were basically the same.The fractal dimension and the total polysaccharide content showed a quadratic linear correlation relationship,the correlation coefficient R²=0.9285.The VFA content of the membrane pool return sludge increased from 90.95 mg/L to 162.70mg/L.In the experiment of ultrasonic coordinated micro-bubbles pretreatment,the dehydration rate and water content,polysaccharides in EPS,VFA,and three-dimensional fluorescence spectrum were used to analyze the mechanism of action.The experimental results show that the maximum VFA content in the treated sludge is204.64 mg/L.And different treatment conditions have different effects on the cracking of EPS and the distribution of organic matter in DOM.Among them,proteins account for 30%～40%of SEPS layer and 40%～50%of LB-EPS and TB-EPS layers in three-layer EPS.The response surface method was used to analyze the effect of three factors on the change of VFA content,and the bubble processing time>ultrasonic time>ultrasonic power.Based on the above studies,fourier transform infrared spectroscopy and scanning electron microscopy were used to analyze the chemical properties and microstructural changes of the sludge after ultrasonic,micro-bubbles,and ultrasonic coordinated micro-bubbles treatment.There are characteristic peaks of polysaccharides and proteins in the supernatant of the sludge.The chemical structure of the organic matter in the sludge has undergone certain changes after the action of ultrasonic and micro-bubbles.The relatively complete floc structure of the original sludge was also broken up under the action of ultrasonic and micro-bubbles,and the porosity increased,which promoted the dissolution of organic matter.Mainly made progress in the research of the following aspects.Firstly,an experimental device capable of treating sludge using ultrasonic and micro-bubbles under continuous flow state was designed.Secondly,the correlation between polysaccharide,particle size,fractal dimension and other indexes was analyzed.The experiment found that there is a strong correlation between the average particle size of the surface area and the polysaccharide,fractal dimension and total polysaccharide content of the LB-EPS layer.The sludge dewatering characteristics were analyzed more comprehensive by individual analysis and correlation analysis.