Study On Ultrasound Controls Technology Of Microcystis Sp. In Water

Algae bloom occurs in ground water due to eutrophication becomes one of theserious environmental problems. Research on algae control technology has importantacademic significance and practical value. According to the problems betweenultrasonic algae control technology and its mechanism, this paper took Microcystis sp.as research object. Acoustic pressure distribution and effective distance in ultrasonicfield, ultrasonic control parameters effects, and the optimal control parameters, kineticslaw of algae control, mechanism, effects of ultrasonic on Microcystis sp., Phycotoxinrelease were deeply studied to discuss the mechanisms of ultrasonic algae control.Acoustic pressure in the ultrasonic field decreased sharply with increasing distance.The higher the input electric power, the greater the acoustic pressure was. The higherthe ultrasonic frequency, ultrasonic energy was absorbed more easily and attenuation inwater was quicker, also with smaller propagation distance and narrower main beam. Butthe near and far field boundary was greater and the directivity was better. This papergave the effective distance and came to such results as follows: low-frequencyultrasound with a wide effective range was suitable for large water. Whilehigh-frequency ultrasound was suitable for emergency alage remove in water treatmentas for the near and far field boundary was relatively far.“Volume density of ultrasonic power radiation” took the two factors of ultrasoundequipment and effective object into account, which could characterize the ultrasoundintensity more accurately and could be calculated through the admittance circle diagrammethod. Considering the influence of ultrasound intensity, algae control rate intuitivelycharacterized the effect of ultrasonic sound on algae control.From Calorimetry and Iodometric method analysis, low-frequency ultrasoundmainly generated the mechanical action. With the ultrasonic frequency increased, thecavitation and chemical reaction increased significantly, producing more free radicals.Cavitation tended to be saturated as frequency increasing to a certain value.Low-intensity ultrasound (below the cavitation threshold) had a common effect on algaecontrol by mechanical action, while the damage to algae was repairable. High-intensityultrasound (above the cavitation threshold) achieved algae control by the combinedeffects of cavitation and mechanical action. As cavitation for the leading role, thedamage to algae was permanent. High-intensity ultrasonic was neither conducive toeconomy nor to water quality with long time’s treatment. From low frequency to high frequency process, the dominant role of ultrasound on algae would also be transformedfrom mechanical action into cavitation.Response surface experimental optimization and two-stage regression model weremade on such algae control parameters as volume density of ultrasonic power radiation,ultrasonic time, ultrasonic frequency and so on, obtaining the optimal controlparameters for frequency of580kHz, volume density of ultrasonic power radiation0.089W/mL, irradiation time24s and the best algae removal rate of99.58%. Algaeremoval met the pseudo-first order kinetics law, reaction rate constant k increasedwith volume density of ultrasonic power radiation and ultrasonic frequency increasing.When reaction rate constant k increased to a certain value, its increase amplitudedecreased and reached a saturation value. The reaction rate constant decreased with theincrease of initial concentration.Ultrasound below the cavitation threshold caused damage to the surface, thylakoidand bubble of Microcystis sp., and cell activity, phycobilisome, photosynthetic systems,buoyancy auto regulating ability were damaged, the net photosynthetic oxygenevolution rate decreased. But the damages were within the limits of its tolerance. Algaecells produced SOD, CAT and other antioxidant enzyme to clear free radicals’ damageto itself generated by ultrasound, so that the MDA content maintained at a lower level,the damage could be repaired, only part of the cell died. Ultrasound above the cavitationthreshold made the thylakoid and bubble of Microcystis sp. fracturing, breaking todissolve and disappearing. Most cells lost the photosynthesis and buoyancy autoregulating ability. Damages to phycobilisome and Chloroplast were unreparable, and themechanism of antioxidant enzyme lost, the cell died finally. High-intensity ultrasoundacted on Microcystis sp. for certain time (<30min), Phycotoxin release was under controland its concentration was under1μg/L of Standards for Drinking Water Quality.