Treatment of raw sewage by sonuv (combined
sonication and UV irradiation) in 90 min was not
effective to mineralize the organic matter. A significant
reduction of COD was observed after 4 h
of sonuv treatment (62).
Ultrasonic can decompose other organic substrates
such as chlorinated hydrocarbons, pesticides, phenol,
explosives such as TNT, and esters, and transform
them into short-chain organic acids, CO2
and inorganic ions as the final products. The time
for complete degradation ranges from minutes to
hours (63).
The application of ultrasound to remove low-concentration
bisphenol A (BPA) in aqueous solution
at the frequency of 20 kHz, and evaluation of
ultrasonic intensity and ozone on BPA removal
was studied (64). BPA was degraded under US
in the presence of CCl4. Also they identified the
main intermediates resulting from BPA ultrasonic
degradation by GC-MS. They found that OH radical
induced oxidation is the major destruction
pathway during BPA sonolysis (64).
The degradation of bisphenol A (BPA) upon ultrasonic
action under different experimental conditions
and evaluation of saturating gas, BPA concentration,
ultrasonic frequency and power has
been studied (65). They found that for 118 μmol/L
BPA solution, the best performance obtained at
300 kHz, 80 W, and oxygen as saturating gas. In
these conditions, BPA readily eliminated by ultrasound
process (90 min). Identified intermediates
were: monohydroxylated bisphenol A, 4-
isopropenylphenol, quinone of monohydroxylated
bisphenol A, dihydroxylated bisphenol A, quinone
of dihydroxylated bisphenol A, monohydroxylated-
4-isopropenylphenol and 4-hydroxyacetophenone
(65)
A novel hybrid advanced oxidation technique
(sonoelectro-Fenton process) was applied for the
degradation of organic pollutants in aqueous medium
(66). They coupled ultrasound irradiation
and the in-situ electrogeneration of Fenton’s reagent.
They studied synergistic action of sonication
in the sono-EF process at low and high frequency.
It was demonstrated that destruction of
herbicides 4, 6-dinitro-o-cresol (DNOC) and 2,
4-dichlorophenoxyacetic acid (2, 4-D) is significantly
accelerated. They concluded that improvement
yielded by sonoelectro-Fenton process
is due to various contributions: (i) enhanced mass
transfer rate of reactants towards cathode, (ii) additional
generation of OH by sonolysis, and (iii)
pyrolysis of organics due to cavitation generated
by ultrasound irradiation (66).
The potential of using ultrasonic irradiation for
the removal of sodium dodecylbenzene sulfonate
(SDBS) at concentrations of 15, 30 and 100 mg/L
from aqueous solutions with power values of 45,
75 and 150 W was studied (67). Results showed
that SDBS conversion decrease with increasing
temperature and initial solute concentration and decreasing
power and frequency. Investigations using
the radical scavengers 1-butanol and KBr revealed
that SDBS degradation proceeds through
radical reactions occurring predominately at the
bubble-liquid interface and, to a lesser extent, in
the liquid bulk. In this research addition of NaCl
or H2O2 had little or even an adverse effect on
SDBS conversion (67).
In another research the effect of various operating
conditions and the presence of matrix components
on the sonochemical degradation of naphthalene,
acenaphthylene and phenanthrene in water
was studied (68). At the operating conditions in
question (initial concentrations of 150, 300 and
450 μg/l, temperatures of 20 and 40° C, applied
power of 45, 75 and 150 W and ultrasound frequencies
of 24 and 80 kHz), all PAHs were susceptible
to sonochemical treatment and, in most
cases, complete degradation could be achieved in
up to 120 min of treatment. Conversion was found
to decrease with increasing initial concentration
and temperature and decreasing power and frequency
as well as in the presence of an excess
of dissolved salts (68).

6- Others Pollutants
LASs are anionic surfactants, found in relatively
high amounts in domestic and industrial
wastewaters. In a study, effectiveness of acoustical
processor for LAS degradation was evaluated
with emphasis on effect of treatment time
and initial LAS concentration (71). Initial LAS
concentrations were 0.2, 0.5, 0.8 and 1 mg/L,
acoustic frequency was 130 kHz, applied power
was 500 W and temperature was 18-20o C. Results
showed that LAS degradation increases
with increasing of sonochemical time. In addition
as concentration increased, LAS degradation
rate decreased in acoustical processor reactor (71).
The effect of 1 MHz ultrasound on inactivation of
Cryptosporidium parvum was studied (72). They
found that continuous irradiation of ultrasound (20
min) increases temperature due to cavitational phenomena.
Ultrasound irradiation of liquid containing
C. parvum showed significant quantitative
changes in pH, temperature and inactivation of
C. parvum (102.7 oocysts killed/s) with a minimum
energy consumption (0.05 oocysts/s) (72).
In another work, the influence of ultrasounds of
diversified intensity (22 and 24 kHz) on iron in
water was studied (73). Variable operational parameters
were vibration amplitude and the exposure
time (1–5 min). Effect of ultrasounds was
studied as a result of influence of sonochemical
oxidation processes and ultrasound coagulation on
iron in the ionized form and on iron-organic complexes
in the low ionized or colloidal form. The
effectiveness of the researched processes was analyzed
from the point of view of the possibility of
determinate intensity ultrasound usage as an unconventional
method of the removal of iron from water.
The degradation of Acid Orange 52 in aqueous
solutions using three processes (photocatalysis,
sonolysis, and photocatalysis with sonication) was
investigated (74). In the case of photocatalysis,
concentration of Acid Orange 52 decreased to
35% in 480 min, but it was decomposed completely
in 300 min using sonolysis. Also concentration
of Acid Orange 52 using photocatalysis
with sonication reached to 0 in 240 min. They
showed that ultrasonic irradiation enhanced the
photocatalytic degradation (74).
In another study the feasibility of sonochemical
reaction technology was studied for degradation
of reactive yellow dye from aqueous solution.
In this study it was shown that the process had
very good results in detention time of 120 min
at 130 kHz and 500 W (75).
The sonochemical decolorization and decomposition
of azo dyes, such as C.I. Reactive Red 22
and methyl orange was investigated (76). They
found that azo dye solutions were readily decolorized
by the irradiation. The sonochemical decolorization
was also depressed by the addition of
the t-butyl alcohol radical scavenger. These results
indicated that azo dye molecules were mainly
decomposed by OH radicals formed from the
water sonolysis. They also proposed a new kinetics
model taking into account the heterogeneous
reaction kinetics similar to a Langmuir-Hinshelwood
mechanism or an Eley-Rideal mechanism
(76).
Application of ultrasound to remove and recover
ammonia from industrial wastewater was studied
(77). They used three different concentrations of
ammonia [5, 10, 15 Vol%] to study the efficiency
of removing ammonia from water. These
concentrations are exactly similar to what may
be found in wastewater resulting from strippers
at petroleum refinery. They found that the ultrasound
has the ability to remove ammonia with
5% concentration to meet the local standard of
treated wastewater within less than 2 h for 0.080
L solution. They also found that as the concentration
of the ammonia increases the removing
of ammonia within 2 h decreases, still the concentration
of the ammonia meets the standard of
the treated wastewater. The ability of the ultrasound
to remove the ammonia failed to produce
any mist when the height of the liquid solution increased,
namely when the height reached (0.0337
m). It means that the device capacity to remove
ammonia has certain limitations based on liquid
heights. The best condition for ammonia removal
was obtained at 5% concentration and 0.080 L
liquid volume (equivalent to 0.0165 m) (77).

Conclusion
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 after irradiation, for the
collapse caused parts of the cell wall to cave in
and consequently the cell surface became uneven.
Furthermore, free radical and sonochemical effects
can arise when inertial cavitation occurs,
which greatly affects passive membrane permeability's,
active transport processes and metabolic
rates (54).
Experiments suggest 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 microorganisms.
The stable cavitation mechanism would
appear to require much higher intensity levels
for such effects (24).
Studies indicate that some degree of an ultrasonic-
induced germicidal effect can be obtained
against fecal coliforms in water. However, absolute
definitive answers have not been achieved
in these experiments. Therefore, additional quantitative
studies will be requiring defining more
fully the exact exposure condition which might
ensure complete germicidal efficacy. Also, results
show that increasing of sonication time proves
fecal coliforms kill as expected. After 90 min of
sonication, 99.95% of bacteria are inactivated and
sonication of smaller volumes produced a more
rapid kill. But in large-scale water treatment plants
90 min sonication times would prove to be uneconomical
at the power used in this work. Therefore,
using higher ultrasonic power is more beneficial
in above process than using low power
and leads to greater efficiency in destruction of
bacterial cells (58).
Treatment of secondary effluent by ultrasonic can
reduce about 30% of the remained organics in
these effluents. This treatment efficiency is probably
the result of organics characteristics. Most of
the organics in secondary effluent are low-volatile.
Besides, it is predictable that most of the
remained matter in effluent have hydrophilic characteristics.
Therefore, it is probable that the main
mechanism of organics removal is treatment by
°OH radicals in bulk solution. Pollutants which
decompose in this region are less degradable by
ultrasound than pollutants which decompose in
gas phase. Besides, secondary effluent contains different
organic compounds with specific characteristics.
Thus, each have different behavior in
treatment by ultrasonic. Moreover, these different
compounds may interfere with the decomposition
process of each other and deteriorate or
enhance the ultrasonic treatment. Inorganic matter
can affect the decomposition of organics too.
Sometimes, treatment by US converts complex
organics to much smaller compounds and it is
obvious that much sonication times are needed
for complete demineralization. Often, relative conversion
of organics suffices for meeting much of
the requirements. As these simple compounds
have organic nature, the effect of treatment can
not be detected by routine tests of COD and
BOD5 and in other words, by these tests it is
difficult to show the effect of ultrasound on
organics decomposition. For example, in Sonooxidation
of humic acids (78), complete degradation
of these compounds occurred in 60 min
whereas, reduction of TOC was only 40%. Suspended
COD has converted to SCOD during
sonication. Previous works on SCOD of wastewater
sludge confirm our result about conversion
of suspended COD to SCOD. For example,
one of the previous studies showed considerable
increase of SCOD of sludge after sonication
such that the SCOD was reported to increase
from 620 mg/L to 2100 mg/L after 2.5 min and
to 4200 mg/L after 10 min (79). The mechanical
shear forces caused by ultrasonic may be the
dominant factor for the disintegration enhancement
(80).
USRT substantially improves the effectiveness
of removing sewage fungi through the effects of
acoustic cavitation in water. Transient cavitation
and stable cavitation need to be considered in
order to gain an understanding of what cavitation
like activity might be responsible for the reduction
of sewage fungi. In propagated ultrasound
reactor, transient cavitation process occurs more
easily at lower ultrasound frequency. As a result,
USRT is suitable for disinfection of sewage fungi.
For effective reduction of fungi using USRT
alone it is almost certain that USRT would need
to be applied in combination with another common
disinfection technologies used in water treatment
including ultraviolet irradiation, ozone or
chlorination. USRT is a very small unit that easily
can be installed at any place in a treatment plant.
Quality USRT can replace sand filters that usually
serve as a step to remove suspended solids prior
to disinfection. There is scientific and economic
potential in the development of combined disinfection
processes. In order to definitely damage
sewage fungi walls higher USRT energy input
is necessary. Also, combination with other disinfectants
applications is useful.
Experiments on LAS degradation showed that
treatment time is the most important parameter
for LAS degradation. Acoustical reactors alone
may not be useful for reducing completely complex
wastewaters of high surfactant load and
could be improved by coupling with other treatment
processes including ozone, UV, chlorination
and H2O2. (71)
From these studies of the effects of ultrasonic upon
the destruction of microorganisms, it can be seen
that ultrasonic is suitable for water disinfection
and can achieve the following:
Remove chlorine from water efficiently (81).
Ultrasonic reduces the amount of chlorine required
for disinfection (81).

Sonication leads to the formation of dead bacterial
cells or selectively destroying weak bacteria (29).
Sonication of smaller volumes produced a more
rapid kill (8).