Cavitation based PI technology for Wastewater Treatment.pptx

1. CAVITATION BASED PI TECHNOLOGY FOR
WASTEWATER TREATMENT
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CAVITATION BASED PI TECNOLOGY FOR WASTEWATER
TREATMENT

2. CONTENTS
Introduction
Cavitation
Principle
Acoustic Cavitation
Hydrodynamic Cavitation
Role of Cavitation in PI
Applications
Wastewater Treatment
Water Disinfection
Reference
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3. INTRODUCTION
• Process intensification (PI) is a way to revolutionize the chemical
process industry in terms of its approach and addresses the issue of
sustainability.
• It can significantly improve energy and process efficiency by
enhancing mixing, mass and heat transfer as well as driving forces.
• Cavitation has been used effectively for process intensification.
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4. CAVITATION
• It is the formation and collapsing of cavities or bubbles in a liquid
mostly developed in the areas which have relatively low pressure.
• Cavitation is categorized into four types on the basis of way of
generation of cavity:
Acoustic
Hydrodynamic
Optic
Particle
• Among these techniques, Hydrodynamic and Acoustic cavitation has
been effective for the desired physico-chemical transformation on a
commercial scale.
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5. PRINCIPLE
• Cavitation is a physico -chemical phenomenon of sequential
generation, development and collapse of the huge amount of
microscopic cavities in liquid medium
• These collapse of cavities release large amount of energy over an
extremely small interval of time
• The energy release is in the format of high temperature and high
pressure.
• The cavitation phenomena involve the generation of free radicals,
local hot spots and microturbulence.
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6. Figure 1:Cavitation phenomenon
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7. ACOUSTIC CAVITATION
• It is due to pressure variations in the liquid when ultrasonic sound
waves propagate through it which consist of compression and
rarefaction phase.
• In rarefaction cycles, the negative acoustic pressure pulls liquid
molecules apart from each other and creates the void in the liquid after
exceeding the critical molecular distance which leads to the formation
of cavities.
• In the compression cycle, acoustic positive pressure pushes the
molecules together and compresses the cavities which collapse in
fraction of time under near adiabatic condition.
• Thus produces high local temperature and pressure condition for small
interval of time (millisecond to microsecond)
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DRAWBACKS
Difficult to use in large scale operation.
Higher operating cost.
Low energy efficiency as compared to hydrodynamic cavitation.
Figure 2: Acoustic cavitation

9. HYDRODYNAMIC CAVITATION
• Liquid passes through the constriction such as an orifice or a venturi
at which kinetic velocity increases at the cost of pressure.
• As pressure drops below vapor pressure, the cavity forms at the throat
of the constriction which get imploded during the pressure recovery in
the downstream of the constriction.
• The cavity implosion results in to very high local energy density also
known as hot spot containing high temperature about 10,000 K and
pressures of 1000 atm.
• This extreme conditions produces the highly reactive free radicals and
enhances mass transfer due to turbulence by cavity collapse.
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Figure 3: Hydrodynamic Cavitation
It is found to be a good alternative to the acoustic cavitation due to its:
High energy efficiency
High cavitation activities
Easy to scale-up
Cost effectiveness

11. ROLE OF CAVITATION IN PI
• To achieve chemical, physical and biological transformation using
conventional approaches involved various limitations such as higher
time, temperature and pressure, required huge amount of toxic
solvents, catalyst and unsatisfactory yields (from commercial angle)
• It has been proved that, use of cavitation can process the reactions that
are naturally slow.
• Cavitationally assisted physico -chemical transformations include
improved selectivity, without or non-hazardous solvents, less energy
consumption and the reaction time
• A significant degree of PI can be achieved by acoustic or
hydrodynamic cavitation.
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12. APPLICATIONS
• In food industry, Acoustic cavitation has been widely applied to aid the
extraction of components of interest from plant sources.
• Preparation of different types of emulsion.
• Effectively utilized for wastewater treatment containing
pharmaceutical discharges, pesticides, dyes and other complex organic
compounds.
• Process intensification of chemical transformation/chemical synthesis.
• Cavitation based depolymerization is a convenient approach to reduce
the molecular weight of the polymers.
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13. WASTEWATER TREATMENT
• The water is getting severely polluted by the hazardous chemicals
discharged from chemical industries such as pesticides, dyes and
textiles etc.
• Their existence in the effluent wastewater even in very small
concentrations is harmful to animals and human beings.
• Over the ages, various techniques such as biological methods,
membrane-based processes, and advanced oxidation processes
(AOP’s) such as photocatalysis, cavitation have been used especially
for the destruction of the bio-refractory pollutants.
• AOP’s can form highly oxidative hydroxyl radicals (●OH) which can
easily oxidize inorganic as well as organic toxic pollutant. Among all
the AOP’s, cavitation is the most energy efficient technique.
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14. MECHANISM
• When exposed to cavitation, the cavities will form and collapse which
creates local hot spots of extremely high temperature and pressure.
• Water molecule dissociate into hydroxyl radicals (●OH) which has
very high oxidation potential and able to oxidize pollutant molecule
present in the wastewater.
• Mainly through two mechanisms:
 Thermal decomposition of the volatile pollutant molecule.
 Reaction of pollutants with ●OH radicals(chemical effect).
• The high intensity of shockwaves formed due to the asymmetric
collapse of the cavity can easily break big pollutant molecule into
small (intermediate) molecules (physical effect).
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15. REACTIONS
The following series of reactions occur during the oxidation of organic
pollutant molecules using cavitation :
H2O +))) ●H + ●OH (1)
●H + ●H H2 (2)
●OH + ●OH H2O2 (3)
●OH + organic molecules CO2 + H2O + some intermediates (4)
Thus, cavitation can also be used as a pretreatment method.
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16. ADVANTAGES
• Pre-treatment with cavitation, followed by the conventional methods
can improve the degradation efficiency.
• Hydrodynamic Cavitation(HC) approach has been tested at an
industrial scale to degrade various organic and inorganic pollutants.
• The combination of HC with AOPs provide the synergetic effect and
gives the desirable outputs, also overcoming the weaknesses of single
AOP techniques.
• The waste streams containing bio-refractory pollutants can be treated
successfully using cavitation.
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17. WATER DISINFECTION
• As cavitation generates hot spots, highly reactive free radicals and
microturbulence associated with acoustic streaming.
• It involves a combination of mechanisms:
1. Mechanical effects
2. Chemical effects
3. Heat effects
• Non-chemical method and does not form any toxic byproducts.
• Energy efficient process.
• Thus can be considered as a process intensification technique for a
large scale water disinfection.
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18. Figure 4 : Conditions for cell disruption during disinfection by
cavitation
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19. ADVANTAGES
• The combination of hydrogen peroxide or ozone with cavitation is
found to increase the efficacy of the destruction of bacteria.
• It can reduce the consumption of chemical disinfectants substantially
in the case of water disinfection.
• It reduces treatment times and the chemical consumption under
optimized conditions.
• It also reduces the formation of the harmful disinfection by-products.
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20. REFERENCE
• Holkar, C.R., Jadhav, A.J., Pinjari, D.V. and Pandit, A.B., 2019. Cavitationally driven
transformations: A technique of process intensification. Industrial & Engineering Chemistry
Research, 58(15), pp.5797-5819.
• Kosel, J., Gutiérrez-Aguirre, I., Rački, N., Dreo, T., Ravnikar, M. and Dular, M., 2017. Efficient
inactivation of MS-2 virus in water by hydrodynamic cavitation. Water research, 124, pp.465-471.
• Burzio, E., Bersani, F., Caridi, G.C.A., Vesipa, R., Ridolfi, L. and Manes, C., 2020. Water
disinfection by orifice-induced hydrodynamic cavitation. Ultrasonics sonochemistry, 60, p.104740.
• Dindar, E., 2016. An overview of the application of hydrodinamic cavitation for the intensification
of wastewater treatment applications: a review. Innovative Energy & Research, 5(137), pp.1-7.
• Ponce-Ortega, J.M., Al-Thubaiti, M.M. and El-Halwagi, M.M., 2012. Process intensification: new
understanding and systematic approach. Chemical Engineering and Processing: Process
Intensification, 53, pp.63-75.
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