Effect Of Ultrasonic Treatment On Content Of Heavy Metals Fraction And Phosphorus Forms In Sewage Sludge

As the scale of China's cities increases,resulting in large sludge production and high treatment costs.The sludge contains not only nutrients such as organic matter,nitrogen and phosphorus,but also harmful substances such as heavy metals and pathogenic microorganisms,which may cause potential ecological hazards to the environment.Ultrasonic technology to crack the excess sludge can not only effectively reduce the moisture content of the sludge,improve the stability of the sludge,but also has a fast processing speed and wide application range.However,in the related research of the technology,there are fewer studies on the changes of phosphorus form and heavy metal form in the sludge solid phase.This paper uses ultrasonic to break the sludge,discusses the effects of ultrasonic treatment time and ultrasonic energy density on the form of phosphorus and heavy metal in the sludge solid phase,and comprehensively analyzes the effects of the content of nutrients and toxic substances in the sludge solid phase by ultrasonic treatment of excess sludge.Ultrasonic treatment of excess sludge,respectively using 0-20 min ultrasonic time and 0-2.4W / mL of ultrasonic energy density to crush the sludge.Through centrifugal filtration,freeze-drying,combined with national environmental protection standards in water quality and soil testing methods,the different morphological distributions and content changes of phosphorus and heavy metals mainly composed of Cu,Zn and Mn were determined.Using the luminescent bacteria as the indicator organism,a 96-well microplate was used as the experimental carrier to determine the inhibition rate of the mixed luminescent bacteria,and the inhibition rate was used to characterize the change of the comprehensive toxicity.The results show that:(1)Ultrasonic dissolving cell action makes the sludge flocculant structure,extracellular polymer and cell wall gradually break to achieve phosphorus release.When the total phosphorus content in the sludge solid phase is reduced to a minimum,reducing by 11.77%,ultrasonic energy density is 1.2W/mL and ultrasonic time is 10 min.Ultrasonic crushing is beneficial to the release of unstable phosphorus into the liquid phase in sludge,but the longer the ultrasonic time is,the greater the ultrasonic energy density is,the higher the biological effective phosphorus began to be enriched,at this time the potential use of sludge as fertilizer is more valuable.(2)When ultrasonic treatment of sludge,the sludge flocculant structure,extracellular polymer and cell wall gradually broken,so that the heavy metal ions which adsorption in the sludge solid equivalent and released into the liquid phase with the sludge broken.Ultrasonic crushing is beneficial to reduce unstable heavy metals in sludge.The longer the ultrasonic time is,the greater the ultrasonic energy density is,so that the stable state of heavy metals began to be enriched.It reduces the degree of potential ecological harm and is beneficial to reduce the harm of sludge discharge to the environment in the long run.(3)The contents of three heavy metals,Cu,Zn and Mn,decrease first and then increase with the increase of time,and are the lowest in 7-13 minutes.The increase of heavy metal Cu with ultrasonic energy density decreased first and then increased,the Cu content was reduced to a minimum and decreased by 15.65% in 1.2W/mL,and the Zn of heavy metal decreased gradually with the increase of acoustic energy density until 2.4W/mL,which decreased by 30.59%.Heavy metal Mn increased first and then decreased with the increase of ultrasonic energy density,and the Mn content increased to the most in 1.2W/mL,and decreased by 19.33% until 2.4W/mL.(4)Ultrasonic treatment is beneficial to reduce sludge particle size and break cell structure in sludge.The greater the ultrasonic energy density is,the longer the ultrasonic time is,the smaller the comprehensive biological toxicity of sludge is.It is indicated that ultrasonic crushing is beneficial to the harmless of residual sludge.To sum up: ultrasonic treatment of residual sludge,phosphorus and heavy metal ions are partially released into the Supernatant by cracking microbial cells and releasing nutrients.Its stable state is enriched in the sludge solid phase,which realizes the stabilization,reduction,harmlessness and resource of sludge treatment.