This document discusses the application of hydrodynamic cavitation as an advanced oxidation process to treat industrial wastewater. It begins by explaining that conventional biological treatment cannot fully degrade non-biodegradable compounds in industrial wastewater. It then introduces hydrodynamic cavitation as an alternative, describing how cavitation generates radicals that can degrade pollutants. The document outlines the experimental setup used, including a venturi tube reactor, and describes the degradation mechanisms of mechanical effects, chemical effects from radicals, and thermal effects. It presents results showing the process can oxidize over 99% of certain compounds. It concludes by discussing the need for further research on pressure profiles, reaction kinetics, and scaling the technology.

1. Presented By
Sivakumar K
Roll No 181657
M.Tech I year, Environmental Engineering
Application of Hydrodynamic Cavitation as
Advanced Oxidation Process to Treat
Industrial Wastewater
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2. List of Contents:
 Introduction
 Cavitation
 Ultrasonic Cavitation
 Hydrodynamic Cavitation
 Advantages
 Experimental Setup
 Degradation Mechanism
 Experiments and Results
 Future scope
 References
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3. Introduction
 Wastewater from Industries like pharmacy, pesticide and petrochemical
process contains large amounts of aromatic compounds, chlorinated
hydrocarbons and phenolic compounds
 These compounds are non-biodegradable or poorly-biodegradable
 Conventional biological process like trickling filters, ASP and oxidation ditches
are unable to completely degrade the pollutants, because these compounds
are toxic to micro organisms
 To treat industrial effluents effectively advanced oxidation processes are
required instead of biological treatment methods
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4. Advanced Oxidation Processes:
 AOPs use ultraviolet light along with ozone and/or hydrogen peroxide to
generate in-situ free radicals like OH.
 These free radicals react with the pollutants at a rapid rate to degrade them
into simple non-toxic molecules
 The operation costs are usually high due to use of UV light and chemical
reactants
 Cavitation phenomenon can be used to generate free radicals by over coming
the above drawbacks
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5. Cavitation
 Cavitation phenomenon consist of the generation, growth and collapse of
bubbles due to pressure pulses
 Cavitation occurs when static pressures of liquid drops below the vapour
pressure
 After reaching maximum size, and as pressure recovery takes place, the non
equilibrium state given rise to bubble implosion
 Implosion of bubbles results in the local increase in temperature and pressure
up to 1000 to 10000 kelvin and 100 to 1000 bar respectively
 Due to extreme pressure and temperature conditions inside the bubbles,
waters dissociates into H
. and OH. radicals
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6.  H
. and OH. radicals are strong oxidizing agents, they grab electrons from
complex compounds and concert them into small non-toxic compounds
 Based on generation of pressure pulse phenomenon cavitation is classified as :
1. Ultrasonic cavitation
2. Hydrodynamic cavitation
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7. Ultrasonic Cavitation
 Ultrasonic cavitation: Pressure waves are generated through an ultrasonic horn
inside a static liquid bulk
 The parameters of pressure pulse are easy to control and reproduce, because
whole process takes place in a static liquid
 Ultrasonic cavitation has proven to efficiently remove a wide variety of
contaminants
Limitations:
 Gives greater efficiency at laboratory scale only but not at industrial scale
 Ultrasonic cavitation has been studied from a scientific point of view rather than
engineering one
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8. Hydrodynamic Cavitation
 Hydrodynamic Cavitation:
Cavitation phenomenon is achieved by pressure deceleration and
acceleration of a liquid flow
Hydrodynamic cavitation reactors:
 Orifice plate reactor
 Venturi tube reactor
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9. Orifice reactor
 A multiple-hole orifice plate offers maximum flexibility
 This kind of reactor may have different arrangement
of holes to achieve the desired cavitation
intensity and cavitation event number
 Dimensions:
 Diameter: 100 mm
 Thickness of plate: 2 mm
 Hole diameter: 2mm
 Distance between holes: 4mm
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10. Venturi tube reactor:
 Venturi tube reactor can generate much lower turbulence intensity compared
with orifice reactor
 This is because of less pressure loss due to its smooth variation of its cross-
sectional area
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11. Advantages:
 This is a simple reactor design with a tank, pump, venturi tube and pipes so
significantly lower operation costs than the rest of the AOPs
 It does not require any external reagents like H2O2 and Ozone for the
generation of free radicals
 The by-products are limited to those expected from the oxidation of the
contaminants, avoiding the presence of other dangerous oxidants such as
chlorine
 Bubble size and density are much higher, implies high reaction volume
 Easy large scale operation compared to ultrasonic cavitation and effective
combination with intensified strategies
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12. Experimental Setup:
 Most common system is closed circulation,
consists of a reservoir, a pump, control valves, a
cavitation reactor and pressure gages
 Water pumped from reservoir branches into two
lines i.e., a main line and by-pass line
 By-pass line is used to control the pressure and
flow rate of water
 Cooling system is used to control the liquid
temperature
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13. Degradation Mechanism:
Treatment of wastewater due to HDC is by means of three mechanisms,
They are,
 Mechanical effects (Shear stress)
 Chemical effects(free radicals)
 Thermal effects(hotspots)
Mechanical Effects:
Strong shear stress generated during bubble collapse can break down
carbon -carbon bond and decompose macro organic molecules into low
molecular organic compounds.
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14. Chemical Effects:
 Water molecules trapped inside the bubble will be decomposed into free
radicals.
 These free radicals will participate in oxidation reactions taking place at the
gas – liquid interface or in bulk liquid
Thermal Effects:
 Local hot spots are generated as bubble radius contracts in pressure recovery
region.
 Under high-temperature conditions of the gas inside the bubble or at the gas -
liquid interface the organic molecules can directly decomposed into low -
molecular organic compounds during bubble collapse.
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15. The total amount of degradation depends on the cavitation intensity and the
number of cavitation events
 Number of cavitation events (C v):
Where, P2 = Fully recovered pressure downstream,
Pv = Saturated vapor pressure of the liquid,
v0 = velocity of the liquid at the constriction position
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16. Experiments:
 Volume of tank: 50 liters
 Flow rate: 5 m3/hr
 Maximum velocity limited in gorge: 30 m/s
 Temperature required: 30oC
 Cavitation period: 15 minutes to 90 minutes
 Air bubbles were pumped to avoid degasification
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17. Results:
 100 ppm dodecane solution (organic aliphatic substance) has oxidized 99%
after 60 minutes of cavitation.
 3000 ppm ammonia solution has oxidized to 1650 ppm after 90 minutes of
cavitation
 Radical traps of salicylic acid were used for indirect measurements
of OH· radicals in order to evaluate the effectiveness of the cavitation loop as
an AOP, obtaining a radical generation of 4 x 1016 OH· radicals/(litre/min)
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18. Future scope
HDC is a well established technology at laboratory scale and more efforts are required
to effectively promote this technology for industrial purpose
 Pressure profiles used in previous studies in cavitation reactor are still not the real
pressure distributions
 More accurate distributions achieved by CFD method should be introduced
 There is a lack of quantitative description of chemical reaction kinetics between
free radicals and contaminants
 Vapour pressure, Solubility, Viscosity, and density of liquid should be correlated
with degradation process
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19.  Present models assume that bubbles collapsed are spherical in shape, realistic
models considering non-spherical bubble collapse are required for accurate
results
 Most of the experiments are conducted in laboratory scale with single
component solution only. Thus unable to quantify the actual analysis
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20. References:
 Advanced oxidation processes for wastewater treatment: Optimization of
UV/H2O2 process through a statistical technique by C.B. Chidambara Raj,
Han Li Quen
 Hydrodynamic Cavitation as a low-cost AOP for wastewater treatment:
preliminary results and a new design approach by Y. Benito, S. Arrojo, G.
Hauke & P. Vidal
 Application of Hydrodynamic Cavitation to Wastewater Treatment by
Yuequn Tao, Jun Cai, Xiulan Huai, Bin Liu, Zhixiong Guo
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21. Thank you
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