Experimental Research On Inhibition And Removal Of Algae By Ultrasound And Its Enhanced Technology

To control water pollution, especially cyanobacterial bloom in eutrophic water,the ultrasonic inhibition and removal of algae were studied including the effect,regularity and influencing factors. And a novel technic for rapid removal of algaespecies, sonication-coagulation, was investigated;the security and cost wereevaluated.The ultrasonic inhibition and removal of algae both own to the mechanicaleffects of acoustic cavitation. The high pressure, shock wave, acoustic streaming andshear force caused by ultrasonic cavitation damaged the cyanobacterial cells,produced pits and holes on the surface, fractured the trichomes, and disrupted the gasvacuole of algae. The filaceous algae with bigger body could be damaged moreeffectively than spherical ones with smaller body in both growth inhibition and cellremoval. And the optimal ultrasonic frequencies for various algae were differentbecause the algae body and the gas vacuole in algae cell were different in size, thusthe resonance frequencies were varied. Along with the increase of acoustic intensity,the cavitation intensity and cavitation-induced algae removal or growth inhibitiontended to be saturated.As a pretreatment method, ultrasonic irradiation within several seconds beforecoagulation could effectively increase algae removal rate in coagulation procedure ofwater works. Its main mechanism was that ultrasonic irradiation within severalseconds influenced the secretion around the algae cell and disrupted the gas vacuolein algae cell, so the algae assembling and settlement were significantly enhanced.Pilot-scale experiment indicated that ultrasound to enhance coagulation removal ofalgae species had an extensive practical application.Through the study of sonochemical degradation of microcystins, it was foundthat ultrasonic irradiation within 5 min did not increase the concentration ofextracellular microcystins. In the technic of algae removal by ultrasound assistedcoagulation, the concentration of microcystins in microcystis suspension decreaseddue to ultrasonic degradation of microcystins and the decrease of coagulant dosageand mix intensity.Ultrasonic pretreatment decreased the cost and increased the removalratio of algae in the coagulation procedure. In the pilot-scale experiment, thecost per ton water was 0.017 yuan when the ultrasonic device was operatedregularly. When the algae concentration of raw water was not high, theultrasonic device could be desuetuded, so the average cost per ton water wasbelow 0.017 yuan.