Cyanobacterial Bloom Control Efficiency And Safety Evaluation Of Low-frequency Ultrasound

Cyanobacterial bloom is one of the environmental problems in lakes and reservoirs all through the world.Developing efficient and safe technology is an important way to alleviate cyanobacterial bloom.In recent years,ultrasound has attracted wide attention due to its advantages such as easy accessibility,low cost,and eco-friendly.The cavitation of low frequency ultrasound is the main mechanism and development direction for algal controlling.In this study,we compared the settling rate of cyanobacterial cells,the destruction of cell structure and the changes in physiological activity of low-frequency ultrasound(20 k Hz)under different power density,duration,and distances to evaluate the efficiency of algae control.We also studied the impact of ultrasound on zooplankton and fish to evaluate its environmental safety.The main results are as follows:1.The efficiency of ultrasound for algae controllingMicrocystis sp.and Cylindrospermopsis raciborskii bloom were collected and treated with ultrasound.The results showed that the efficiency of ultrasound is positively correlated with power density and duration,and negatively correlated with treating distance.The potency ratio of ultrasound was optimal under 0.040 W/m L of the power density and 60 s of the duration.The sedimentation rates of Microcystis sp.and Cylindrospermopsis raciborskii cells were 73.3% and 58.0%,respectively.The efficiency of ultrasound on cyanobacteria was significantly higher than that of chlorophyta and diatoms.According to the fitting analysis,the effective controlling distance of the device is about 2.6 m.2.The physiological effects of ultrasonic treating on algal cellsWe compared the changes of physiological activity such as superoxide dismutase(SOD),catalase(CAT),peroxidase(POD),malonaldehyde(MDA)and adenosine triphosphate(ATP)of algal cells under the treatment of ultrasound.The results showed that there was a certain degree of oxidative damage to algal cells.The more seriously oxidative damage was observed under the higher power density and the longer duration.The ultrastructural changes of algal cells showed that thylakoid and gas vesicle were destroyed obviously.The photosynthetic system was also damaged,and the cell transmittance decreased.But there was little damage for the cell membrane.3.The ecological safety of ultrasoundDiaphanosoma dubia and Calanoida sp.were treated with 0.040 W/m L of ultrasound for 60 s per day and the duration of 24 days,it was found that ultrasound had little effect on the survival of the zooplankton.The concentration of total algal toxins(dissolved and algal cell-bound)was significantly reduced and positively correlated with power density and duration.The antioxidant enzyme activity of tilapia has little change under the treatment of ultrasound(0.040 W/m L,60 s),and no fish died.