1. WET AIR OXIDATION Dr. V.V MAHAJANI Professor of Chemical Engineering,
Institute of Chemical Technology, Matunga, Mumbai 11
E.mail
Phone : (022) (Extn 2015)
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2. WELCOME
TO ALL
v.v.mahajani, uict

3. CHEMICAL PROCESS INDUSTRY ( CPI) BIRD’S EYEVIEW
UTILITIES GASEOUS WASTE
RAW MATERIALS PRODUCTS, By PRODUCTS,
INTELLECTUAL SOLID WASTE
INPUTS LIQUID WASTE (~ 90 % of water in)
CPI
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4. Chemical Engineer’s View
BIO PROCESSES PHYSICO CHEMICAL PROCESSES
Aerobic SEPARATION BULK MINERALIZATION
Anaerobic Liquid / Liquid Extraction Incineration
Precipitation Wet Air Oxidation
Adsorption POLISHING PROCESS
Membrane Photo Chemical
2. REACTIVE DESTRUCTION Fenton
Hydrotreatment Sonication
Ozonation
HYBRID PROCESSES : INNOVATIVE COMBINATION OF ALL
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5. LIMITATIONS V V M 3 PROCESS PRE-VIEW BIO-PROCESSES
MOST POPULAR PROCESSES OPERATING AT NEAR ATM PRESSURE AND
AMBIENT TEMPERATURE.
BIO GAS GENERATION FROM SPENT WASH OF A DISTILLERY UNIT
LIMITATIONS
SLOW RATES, LARGE VOLUME. HENCE, MORE FLOOR AREA REQD.
OFTEN NEED ENGINEERED MICRO-ORGANISMS
DO NOT PERMIT, INVARIABLY, SHOCK LOADS, TOXIC WASTES
NEEDS ELABORATE POLISHING TREATMENT FOR WATER RECYCLE
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6. WATER COSERVATION RESULTS IN
CONCENTRATED WASTE
X NOT SUITABLE FOR BIO PROCESS
OPTIONS AVAILABLE:
INCINERATION
WET AIR OXIDATION
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7. INCINERATION : HIGH OPERATING COST. LOWER CAPITAL INVESTMENT..
WATER CAN NOT BE RECYCLED UNLESS TREATED.
DEPRECIATION BENEFIT IS ONLY FOR CAPITAL
INVESTMENT AND NOT FOR OPERATING COST.
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8. MORE APPROPRIATELY : THERMAL PROCESS.
WET AIR OXIDATION
MORE APPROPRIATELY : THERMAL PROCESS.
IT IS SUBCRITICAL OXIDATION PROCESS IN AN AQUEOUS MEDIUM
Water Tc = C & Pc = atm
OXIDATION OF ORGANIC INORGANIC SUBSTRATE IN PRESENCE OF MOLECULAR O2 T = 100 _ 250 0C; Pressure: O2 pressure 5 to 20 atm
O2 Solubility in water is minimum at near about 100oC. Above 100 oC it is increasing with increase in temperature.
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9. OXIDATION REACTION FREE RADICAL MECHANISM
O2 + H2O OH* via OH* radical formation
NON SELECTIVE OXIDATION TO MINERALIZE OXIDIZABLE CONTAMINANTS
ORGANICS O2
Ca Hb Nc Pd Xe Sf Og C CO2
H2O N N2, NH3, NO3, H H2O
P PO4
X HX (halogen)
S SO42-
O2 O2
Inorganic substances
Na2S Na2SO4
Na2SO Na2SO4
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10. OXIDATION POWER OF COMMON OXIDIZING AGENTS RELATIVE TO OXYGENCl
ClO
HOCl
H2O O
OH* (hydroxyl radical) 2.33 F
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11. SHE management does not allow use of “F”
HIGHER OXIDATION POWER MEANS A RELATIVE LACK OF
SELECTIVITY.
This property IS USELESS for organic synthesis but the most desirable in waste treatment.
SHE management does not allow use of “F”
WET Oxidation Technology is centered around OH* radical as non-selective but powerful oxidizing agent.
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12. V V M 10 INSIGHT INTO REACTION MECHANISM organic substrate
Large molecular wt O CO H2O
organic substrate
low mol. wt organic acids
(Acetic, Propionic, Glyoxalic, Oxalic)
Complex Reactions
Intermediates are formed and can be slow to oxidize or mineralize to CO2
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13. KINETICS
The waste is characterized as: BOD (bio-chemical oxygen demand), COD ( chemical oxygen demand ) & TOC ( total organic carbon )
Kinetics is presented in terms of COD / TOC reduction
Instead of having complex kinetics representing series and parallel reactions, a series
reaction approach is considered. We have found that a lumped parameter series
reaction in terms of COD is more design friendly
k1 k2
(COD) (COD) CO2 and H2O
Original low mol. wt
Waste intermediates
In majority of cases, the second reaction step (k2) is the rate limiting step.
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14. The kinetics is then given as
 d(COD) = k (COD)m (O2)n dt
m  1 ; n varies with 0.5 to 1.0
CATALYSTS
Wet air oxidation reactions can be catalyzed by
homogeneous catalysts
heterogeneous catalysts
to reduce SEVERITY of operating conditions.
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15. CATALYST CHARACTERIZATION
Homogeneous catalysts
The catalyst should be such that complete oxidation of substrate is possible to CO2 and H2O.
It should be compatible with MOC of the reactor.
It should be easily recoverable.
CATALYST RECOVERY
Homogeneous catalysts could be recovered by
Precipitation
Ion exchange technique
Liquid emulsion membrane process
The leached catalyst and support can be recovered also by the above techniques.
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16. Heterogeneous catalysts
Cu, Co, Mn, Fe, Ru could be supported on suitable support such as Al2O3, SiO2 and TiO2
Temperatures are around 200 oC and there exists acetic acid as an intermediate. This could result in extraction/leaching of the catalyst element into treated aqueous stream.
Leaching of support also may take place.
We have observed:
Cu salts are very good for complete mineralization
Co and Fe are not able to oxidize acetic acid as effectively as copper
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17. Advantages and Limitations
It can handle concentrated waste COD 10, ,000 mg/l
It can handle toxic chemicals cyanides, sulphides and priority pollutants
Waste with high TDS can be handled
Energy integration possible
Very less space, even it can be underground.
Lower operating cost
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18. Capital intensive due to exotic MOC.
Limitations
Capital intensive due to exotic MOC.
However, depreciation benefit makes it attractive!
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19. Typical Continuous Wet Oxidation System for Liquid Waste
ENERGY RECOVERY
SYSTEM
TREATED
WATER
EFFLUENT
AIR
WET OXIDATION
REACTOR
SATURATOR
AIR COMPRESSOR
Typical Continuous Wet Oxidation System for Liquid Waste
BFW
STEAM
OFFGAS
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20. Integration with other waste treatment processes:
It is possible to have hybrid systems to realize economic advantage
of the waste treatment process.
1 Membrane – WAO
2 WAO - Membrane
3 Sonication – WAO
4 Fenton – WAO
5 Biological treatment – WAO
6 WAO - Biological treatment
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21. We can use following guidelines for water recycle in a chemical plant
A SYSTEMATIC APPROACH FOR WATER TREATMENT FOR RECYCLE
We can use following guidelines for water recycle in a chemical plant
Identify contribution of water bill in the cost of production.
Identify the scenario around your project with special reference to availability of water in future, considering your future requirements due to expansion.
Take water balance in your plant.
Identify all water outlets such as plant effluent, utility blow downs, water used in administrative block, canteen etc. Please note that one can do little to evaporation loss in cooling tower.
Have detailed analysis of each effluent stream and decide which can be used for recycle and which can be used for purging. It may be possible to use purge water for gardening and horticulture.
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22. Decide on treatment strategy.
Have specifications for water use at all process blocks in the project For instance, specifications for water used for washing filters would be totally different from that used as boiler feed water generating steam for captive power generation also.
Decide on treatment strategy.
Since each effluent stream is unique, carry out bench scale studies.
Carry out detailed technoeconomic feasibility study to ensure that set goals or targets could be achieved / realized.
Implement the project without any delays.
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23. WE LEARN TO RESPECT THE DIGNITY OF ENVIRONMENTAL PROTECTION
SUSTAINABLE DEVELOPMENT OF MANKIND
IS POSSIBLE ONLY WHEN
WE LEARN TO RESPECT THE DIGNITY
OF ENVIRONMENTAL PROTECTION