Ultrasonic technology uses high frequency sound waves to treat water and wastewater through a process called cavitation. Cavitation occurs when sound waves cause bubbles to form, grow, and violently collapse in the liquid, generating high temperatures and pressure that can break down organic compounds. This document reviews the science behind cavitation, including how piezoelectric transducers generate ultrasound, the formation of hydroxyl radicals, and the differences between transient and stable cavitation. Applications include suppression of algae growth and biofilm formation without using chemicals.

3. MAIN MOTIVE

5. ABSTRACT

6. Ultrasonic Technology as an innovative technology may
be used for water and waste-water treatment for
pollution removal. This technology acts as an advanced
oxidation process. Application of this technology leads
to the decomposition of many complex organic
compounds to much simpler compounds during
physical and chemical compounds during cavitation
process. In this article review, some applications of this
valuable technology are presented.

8. INTRODUCTION

9. Elastic waves with frequencies ranging Sound theory
from 109 to 1012 or 1013 Hz, basically the high
frequency portion of the spectrum of elastic waves is
known as hyper sound. The physical nature of hyper
sound is no different from that of ultrasound, whose fre
quency ranges from 2 x 104 to109 Hz.
The hypersonic frequency range corresponds to the freq
uencies of electromagnetic oscillations in the decimeter,
centimeter, and millimeter ranges (the so-called super
high frequencies, or SHF).
What is Hyper Sound?

11. Sound Theory:
Most modern ultrasonic devices rely on transducers which are
composed of piezoelectric materials. Such materials respond to the
application of an electrical potential across opposite faces with a small
change in dimensions. This is the inverse of the piezoelectric effect. If
the potential is alternated at high frequencies, the crystal converts
electrical energy to mechanical vibration (sound) energy. At
sufficiently high alternating potential, high frequency sound
(ultrasound) will be generated. When more powerful ultrasound at a
lower frequency is applied to a system, it is possible to produce
chemical changes as a result of acoustically generated cavitation.
Frequencies above 18 kHz are usually considered to be ultrasonic. The
frequencies used for ultrasonic cleaning, range 20 kHz to over 100 kHz.
The most commonly used frequencies for industrial cleaning are those
between 20 and 50 kHz. Ultrasound has wavelengths between
successive compression waves measuring roughly 10 to 0.001m. These
are not comparable to molecular dimensions. Because of this
mismatch, the chemical effects of ultrasound cannot result from a
direct interaction of sound with molecular species.

13. Bubble Cavitation:
Ultrasound Reactor Technology (USRT) in a liquid leads to the acoustic
cavitation phenomenon such as formation, growth, and collapse of bubbles
(cavitation), accompanied by generation of local high temperature, pressure,
and reactive radical species (°OH , °OOH) via thermal dissociation of water
and oxygen. These radicals penetrate into water and oxidize dissolved organic
compounds. Hydrogen peroxide (H2O2) is formed as a consequence of °OH
and °OOH radical recombination in the outside of the cavitation bubble.
Concentration of HO° at a bubble interface can be as high as 4x10-3 M, which
is 108 -109 times higher than that in the other advanced oxidation processes.
Pyrolysis of pollutants could lead to radical formation and starting chain
reactions, e.g. degradation of carbon tetrachloride. The basis for ultrasound
irradiation applications is that acoustic cavitation can create a number of
mechanical, acoustical, chemical and biological changes in a liquid.
Bubbles form, grow and subsequently collapse through compression-
rarefaction cycles. Temperature in collapsing bubbles can reach to 3000-
5000°K and pressure to 500-10,000 atm. Under such extreme conditions,
water molecules undergo haemolysis to yield hydroxyl radicals and hydrogen
atoms. Since oxidation by hydroxyl radical is an important degradation
pathway, amount of the hydroxyl radicals present in the sonolysis system is
directly related to the degradation efficiency.

15. Types Of Bubble Cavitation:
There are mainly two types of acoustic cavitation.
(i)Transient &
(ii)Stable or, Controlled
Transient cavities exist for a few cycles, and are followed by a rapid and violent
collapse, or implosion, that produces very high local temperatures. Ultrasonic
cleaning frequencies transform low-energy/density sound waves into high-
energy/density collapsing bubbles, producing transient acoustic cavitation.
Transient acoustic cavitation can cause damaging surface erosion in more sensitive
substrates. Totally weaken or disrupt bacteria or biological cells by ultrasonic could be
attributed to following processes. Forces due to surface resonance of the bacterial cell
are induced by cavitation. Pressures and pressure gradients resulting from the
collapse of gas bubbles which enter the bacterial solution on or near the bacterial cell
wall. Bacterial cell damage results from mechanical fatigue, over a period of time,
which depends on frequency. Shear forces induced by micro streaming occurs within
bacterial cells. Chemical attack due to the formation of radicals during cavitation in
aqueous media. These radicals attack the chemical structure of the bacterial cell wall
and weaken the cell wall to the point of disintegration. Amongst final products of this
sonochemical degradation of water is hydrogen peroxide, which is a strong

17. PROCESS OF BUBBLE
CAVITATION

19. REVIEW

21. BASIC THEORY OF
CAVITATION

22. Basically it’s a boiling process of water with the help of
Ultra Sonic sound frequencies. Ultrasound does not boil at its
own. But, it creates a very rapid agitation in the liquid which
leads to increase in kinetic energy creating rapid collisions and
hence releases energy in the form of heat. The heat starts heating
up the liquid. And if Ultrasound is provided long enough, it may
start boiling water. But there are good chances that our liquid will
boil off below its normal boiling point because application of
Ultrasound increases surface area of the liquid hence increased
interracial area between atmosphere and liquid, which triggers
natural convective evaporation to higher extent as rate of heat
transfer is proportional to interface area. Furthermore it
generates bubbles due to intense pressures of waves which when
collapses at the surface ejects tiny droplets which are in liquid
phase but small enough to get airborne. Like mist.

24. APPLICATIONS

26. ADVANTAGES

27. 1. Suppression of algal growth and biofilm formation.
2. These kind of ultrasound algae control systems can be used in all
situations where water is stored, from large industrial water
applications to small private pools or ornamental ponds. These
systems range from large capacity units to small ones, enabling a
'tailor-made' solution to all purposes.
3. Ultrasound systems do not use chemicals, only needs a low supply
of electrical energy, and does not harm plants, fishes, zoo-
plankton, and other types of life present in the water, thus having a
low environmental impact.
4. Environmentally friendly as there are no pollutants associated with
this method of water treatment.
5. Inactive bacteria, pathogen, virus in the water supply by removing
and killing micro-organism.
6. Cost effective and low operating cost and savings in
consumables.
7. No more cleaning of UV tubes and chamber.

28. DISADVANTAGES

29. 1. The cleaning action will be very abrasive. So abrasive
can ablate away the stainless steel the tank is made out
of.
2. Occupational exposure to ultrasound in excess of 120 dB
may lead to hearing loss. Exposure in excess of 155 dB
may produce heating effects that are harmful to the
human body, and it has been calculated that exposures
above 180 dB may lead to death.
3. In contrast to many other processes which are negatively
affected when suspended solids of effluent increase,
efficiency may even improved by increase of turbidity
suspended solids.

30. PRECAUTIONS

31.  To obtain the successful treatment of the water, one
should first know that no water body is the same, every
water body is unique and should be treated uniquely.
 Some industries use an ultrasonic cleaner at work. The
water with wetting agent (a very dilute detergent) gets
very hot. They don’t use it with just distilled water as the
instruction manual advises not to.
 This report recommended an exposure limit for the
general public to airborne ultrasound sound pressure
levels (SPL) of 70 dB (at 20 kHz), and 100 dB (at 25 kHz
and above).

32. CONCLUSION

33. Cavitation is a nonthermal mechanism of ultrasonic irradiation that
occurs when the gas vesicles are acted upon by a sufficiently intense
ultrasonic irradiation of 42 kHz. Observation of differential
interference microscopy showed the collapse of the gas vesicles
irradiation, for the collapse caused parts of the cell wall to cave in
and consequently the cell surface became uneven. Furthermore, free
radical and sono-chemical effects can arise when inertial cavitation
occurs, which greatly affects passive membrane permeability's,
active transport processes and metabolic rates. Experiments
that ultrasonic in low-kilohertz frequency range has some efficacy in
inactivating some disease agents in water. This would suggest that
transient cavitation is the physical mechanism responsible for
affecting the micro-organisms. The stable cavitation mechanism
would appear to require much higher intensity levels for such effects.
Sonication leads to the formation of dead bacterial cells or
destroying weak bacteria. Sonication of smaller volumes produced a
more rapid kill.

34. REFERENCES

35. 1. Nikolopoulos & Papayannakos : Ultrasound assisted
kinetics and intra-particle diffusion effects.
2. Petrier C. : Unexpected frequency effects on the rate of
oxidative processes induced by ultrasound.
3. A.H. Mahvi : Application of Ultrasonic Technology.
4. https://www.youtube.com/watch?v=0dd6AlyOnfc
5. https://www.youtube.com/watch?v=qGSioE58YjA
6. Wikipedia.org