|M.Sc Thesis||Department of Civil and Environmental Engineering|
|Supervisors:||Assoc. Prof. Friedler Eran|
|Dr. Ram Porat|
|Full Thesis text - in Hebrew|
Planktonic algae form a nuisance in water bodies. In drinking water reservoirs these algae are the main cause of increases in turbidity, off-color, taste and odor. In treated wastewater storage reservoirs the main inconvenience is the clogging of irrigation filters and drippers. Toxic cyanobacteria (Bluegreen algae) are a potential for environmental and health problems in drinking water reservoirs and natural water bodies as well.
Ultrasonic irradiation has been found to be harmful to the structure and the functioning of various organisms, probably via the mechanisms of cavitation or resonance. The effects have been noted on different organisms depending on the power transmitted and the frequency of the ultrasonic irradiation.
The goal of this research was to test the long-term efficiency of commercially available low-intensity ultrasonic irradiation devices as a means to reduce nuisance algae in various water bodies. Three commercial devices were tested: Two transducers with a broadcast frequency of 25-35 kHz and power output of 45 Watts, and a third transducer having a broadcast frequency of 1.3-1.6 MHz and power output of 90 Watts.
The experiments were carried out in field studies with three different systems:
1) A 75 hectare storage reservoir for the Israeli National Water Carrier (INWC) at the Eshkol site. 2) 0.25 hectare overflow ponds from the INWC Eshkol Site; 3) 0.04 hectare commercial fish ponds in a local hatchery.
Statistical analysis of the experimental results indicated almost no effect of the ultrasonic transducers on algae biomass and population in any of the experimental systems examined. The ultrasonic transducers did not cause any notable change to gas vesicle content or reduce buoyancy of cyanobacteria.
In some experiments, however, one of the transmitters (~30 kHz, 45 W) may have slightly reduced the population biomass of the Green algae group.