| In recent years, eutrophication phenomenon in China is becoming increasingly serious.The high frequency of cyanobacteria blooms caused by it is bringing rising levels of environmental pollution and great harm to the people’s production life.Microcystin aeruginosa is the most representative dominant species of the cyanobacteria algal blooms and the main pollutants of the water bloom.Ultrasound technology is a new type of environment-friendly technology rising in recent years.Ultrasound produce extreme environments such as high temperature or high pressure when travelling in water,which can degrade and destroy water pollutants.In this paper,ultrasound is used as the main approach-combined with Fenton and chemical coagulation ultrasound-in studying on the technology of removing Microcystis aeruginosa,which may provides technical support for the ultrasound used in practical engineering applications.First of all,the paper studys the role of ultrasound on the direct removal and growth inhibition of Microcystis aeruginosa. Research shows that200KHz of ultrasonic irradiation has the best inhibition effect on Microcystis aeruginosa.Ultrasonic irradiation for four minutes rated at70W.2-3days later,the amount of biomass in ultrasound group is only about50%of the control group.Using ultrasound to remove algae directly meets the first-order kinetics reaction in a certain time.When using low-frequency ultrasound,frequency of20KHz works best on algae removal,rated at150W,10min later the biomass of Microcystin aeruginosa decreases by50.2%.When using high frequency ultrasound,800KHz works best,rated at50W, the biomass of Microcystin aeruginosa reduce33.3%after60minutes’ ultrasonic irradiation.Secondly,studies show that dual-frequency and multi-frequency ultrasonic algae removal effect is superior to single-frequency ultrasound,which means that multi-frequency ultrasound has synergistic effects on the removal of Microcystis aeruginosa.Fenton technology with ultrasonic algae is preferable to using ultrasound or Fenton technologies separately.When the concentration of H2O2is0.2mmol/L,1:4Fe2+/H2O2, ultrasonic algae removal works best.After60min ultrasonic radiation, the biomass of Microcystin aeruginosa reduced from0.239to0.140. PH=8.9, temperature of35℃, algae removal works best,and free radical scavenger and aeration have an important impact on ultrasonic algae removal.In the end, studies show that PAC,FeCl3and the PFS have different coagulation effects on Microcystis aeruginosa.With the same concentration,turbidity removal rates highest for PFS.When the addition of PFS is10mg/L,turbidity removal rates reach90%or more.Moreover,ultrasound plays an enhanced role in coagulation.With the same concentration, algal turbidity removal efficiency after ultrasonic irradiation can be increased by about15%.The best power of ultrasound enhanced coagulation is40W, with the time of15s to20s.Frequency effect on coagulation is not obvious.Using method of images to make fractal dimension calculation on flocs produced by three kinds of coagulants.With the same addition amount, the fractal dimension of the three coagulants were1.44,1.74,1.78.Flocs after PFS coagulation are large,uniform, and easy to settle.Orthogonal experiment is designed to examine the effects of three factors on the morphology of the flocs.Results showed that the amount of the coagulant has the greatest impact on the shape of the flocs,with the range of0.37.Ultrasound frequency and power have a smaller effect on flocs form with the range of0.07and0.03.Cost and other factors are integrated to conclude that the best conditions are in the frequency of800KHz, power of60W. When the concentration of PFS is10mg/L,the flocs are the largest and easy to settle. |
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