Green algae and diatoms have
been found to be damaged by sound waves in studies with frequencies ranging from
20 khz to 60 khz putting it in the ultrasonic region. The damage is done by
resonating the inner cell wall that generates a sympathetic rebound and
ultimately causes a tear between it and the contractile vacuole that regulates
the internal pressure. The inner cell wall is called the plasmalemma and its
structure and design can vary widely between different types of algae. Once it
is broken from the contractile vacuole, it will collapse inside the outer algae
sheath an d c ause the cell to die. It is impossible to know what is the exact
frequency that damages each type of algae. There are estimated to be upwards to
100000 different species. Our control strategy takes the range of 24 to 64 khz
and covers it with 79 frequencies within that range. The idea is to get close
enough to a resonating frequency to create the damaging effect. As algae grow
and reproduce, they likely go through a number of frequencies that may be
damaging to them, so you don’t have to be exact, just close
enough.
Cyanobacteria are different than
green algae. They have gas vesicles that are only one protein layer thick and
easy to break. They only learned what these things looked like in the early
1970’s. The ultrasonic device does not kill them directly, but breaking the gas
vesicles causes them to lose buoyancy so they sink out of light and die. Since
the device is not strong enough to break the outer cell wall, the trapped gas
from the vesicles migrates to the outer wall and slowly leaks through in about 3
days. To see this effect you need an electron microscope. Gas vesicles are
extremely tiny and there are hundreds in each cyanobacteria
cell.
Some scientists believe that it
is cavitation that causes the damage, but if you do the math you will see that
it would be impossible to create a cavitation zone large enough to be effective
and even if you did, the ultrasonic device would be prohibitively expensive.
This belief stems from early work in this field by Paul Langevin, the French
scientist that developed sonar in the early 1920’s. They noted that algae died
around the sonar test sight and since the device created a cavitational field,
they assumed that cavitation, a very strong force related to turbulence, was
responsible. In the 1890’s they noted similar effects when algae blooms
disappeared around mining sites where dynamite was exploded underwater. In this
case the shockwave of the explosions caused the damage.
Some algae are so complex
internally that it is difficult to cause them to resonate and be damaged. Types
that are similar to plants with true branching filaments are generally not
affected by the technology. In the last two years we learned that a difficult
blue-green algae (Lyngbya) can be damaged by a slightly higher energy output
level. We were the first to note this and are working to improve upon this
finding.
One last piece of information
that you may find interesting is that facultative anaerobic bacteria are
influenced by the sound waves. They behave as if they are in turbulent water
conditions where they do not seek to reproduce in such turbulent water. We have
used this finding to keep tanks and water processing equipment clean from
biofilm growth.
George Hutchinson, President, AlgaeControl.US
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