INDUSTRIAL WASTE WATER TREATMENT :

ZERO DISCHARGE ?

Professor (Dr) V. V. Mahajani

Contact : 0251 – 249 68 85+91 900 4266 456, Email: vvmahajani@gamil.com 1mahajani

ZERO DISCHARGE : A MYTH !

Near zero discharge = Distinct Possibility

Question : At What Cost ?

• Cost to Project Owner

• Cost to Society

• Cost to Environment

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Industrial waste water contains:

• Priority Pollutants,

• BOD biodegradable waste,

• COD non biodegradable waste,

Metals.• Metals.

Discharge specifications are discharge point specific.

The State Industrial Development Corporations designs specifications.

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WAR for WATER is a common local phenomenon.

Water precipitation on our planet Earth and in India is almost constant

Water demand is growing; Population is growing & so

• Water demand for human Consumption• Water demand for human Consumption

• Agriculture

• Industrialization

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• AGRICULTURE & INDUSTRIALIZATION, BOTH MUST GROW TOGETHER FOR OUR SUSTAINABLE DEVELOPMENT.

• Both need WATER

vNearly 90 % of water used in Industry results in an effluent-vNearly 90 % of water used in Industry results in an effluent-industrial waste.

•Diverse nature of industry results in wide variation in effluent quality.

•Water conservation results in concentrated waste resulting invery high COD / BOD ratio.

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WE NEED A PROCESS WHICH CAN

MINERALIZE ALL COD TO MAKE IT POSSIBLE

TO RECOVER GOOD QUALITY WATER.

THE OBVIOUS CHOICE IS

ADVANCED OXIDATION PROCESS

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ADVANCED OXIDATION PROCESSES:

All Processes dealing with oxidation with OH* (hydroxyl radicals)

are Advanced Oxidation Processes.

LIMITATIONS OF BIO PROCESSES:LIMITATIONS OF BIO PROCESSES:

•SLOW RATES, LARGE VOLUME. HENCE, MORE FLOOR

AREA IS REQUIRED.

•OFTEN NEED ENGINEERED MICRO-ORGANISMS

•DO NOT PERMIT, INVARIABLY, SHOCK LOADS

•NEEDS ELABORATE POLISHING TREATMENT FOR WATER

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v Wet Air Oxidation

• Fenton Chemistry

• Ultra Violet (UV)

ADVANCED OXIDATION PROCESSES:

• Ozonation

• Sonication

• Electro destruction

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OXIDATION POWER OF COMMON OXIDIZING AGENTS

RELATIVE TO OXYGEN

O2 1.00

Cl2 1.06

ClO2 1.06

HOCl 1.24HOCl 1.24

H2O2 1.48

H2SO5 1.51

O3 1.68

OH* (hydroxyl radical) 2.33

F2 2.50

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•HIGHER OXIDATION POWER MEANS A RELATIVE

LACK OF SELECTIVITY.

vThis property IS USELESS for organic synthesis but the

most desirable in waste treatment.

SHE management does not allow use of “F”. Hence next automaticSHE management does not allow use of “F”. Hence next automatic

choice is OH* hydroxyl radical.

Advanced Oxidation Technologies are centered around OH* radical

as non- Selective but powerful oxidizing agent.

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n MORE APPROPRIATELY : THERMAL PROCESS.

n IT IS A SUBCRITICAL OXIDATION PROCESS IN AN AQUEOUS

MEDIUM

Water Tc = 374 oC & Pc = 217.6 atm

WET AIR OXIDATION

n OXIDATION OF ORGANIC SUBSTRATE IN PRESENCE OF

MOLECULAR O2 T = 100_250 oC

& Pressure: O2 pressure 5 to 20 atm

Ø O2 Solubility in water is minimum at near about 100oC.

Ø Above 100 oC it is increasing with increase in temperature.

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OXIDATION REACTION

FREE RADICAL MECHANISM via OH* radical formation

NON SELECTIVE OXIDATION TO MINERALIZE OXIDIZABLE CONTAMINANTS

O2Ca Hb Nc Pd Xe Sf Og C CO2

H2O N N2 or NH4+ or NO3

-

H H2OP PO4

-3

X HX (halogen)X HX (halogen)S SO4

2-

Inorganic substancesO2

Na2S Na2SO4Na2SO3 Na2SO4

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The waste stream consists of complex and simple molecules

The waste is characterized as

BOD (bio-chemical oxygen demand)

COD ( chemical oxygen demand)

KINETICS:

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

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Large molecular wt. + O2 CO2 + H2O organic substrate

low mol. wt organic acids

REACTION MECHANISM

k1

k2 k3

low mol. wt organic acids(Acetic, Propionic, Glyoxalic, Oxalic)

ü Complex Reactions; Intermediates are formed and can be slow to oxidize or mineralize to CO2

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We have found that a lumped parameter series reaction in

terms of COD / (TOC) is more design friendly:

k1 k2(COD) (COD) CO2 and H2OOriginal low mol. wtWaste intermediatesWaste intermediates

In majority of cases, the second reaction step (k2) is the rate limiting step.

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The kinetic expression is then:

m ≈ 1

n varies with 0.5 to 1.0

nO

mnm PCODkOCODkdt

CODd)()()()(

)(222 ==−

n varies with 0.5 to 1.0

This is applicable to homogeneous reaction

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CATALYSTS

Wet air oxidation reactions can be catalyzed by

Ø homogeneous catalysts

Ø heterogeneous catalystsØ heterogeneous catalysts

to reduce operating conditions.

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Ø Homogeneous catalysts

n The catalyst should be such that complete oxidation of

substrate to CO2 and H2O is possible

n It should be compatible with MOC of the reactor.

n It should be easily recoverable

n It should be easily available

n It should be cheap

n It should be possible to meet SHE compliance with ease.

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HETEROGENEOUS CATALYSTS:

ADVANTAGE : EASE OF SEPARATION.REACTOR CAN be :

Slurry reactor (Mechanical Agitated Contactor)Bubble column ( Circulating Bubble Column)Packed bed (Adiabatic)

Limitations:• Slower rate, (?)• Slower rate, (?)• Possibility of the catalyst leaching in the solution.At prevailing high temperatures, t > 200 oC, intermediate acetic acid

formed can react with catalyst metal elements forming water soluble metal acetates thereby reducing active centres on the catalyst

Ø Please note homogeneously catalyzed reaction will effectively enhanced the rate.

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THE CATALYST CHOICE IS WASTE SPECIFIC.

Bench Scale Screening is highly recommended.

EVERY WASTE IS HAVING RADICALLY DIFFERENT

CHARACTERISTICS .

Ø BENCH SCALE PAPRAMETER

OPTIMIZATION IS ALWAYS DESIRED

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Advantages

n It can handle concentrated waste COD 10,000-

500,000 mg/l.

n It can handle toxic chemicals such as cyanides,sulfides, chlorophenols, amines, metals and prioritypollutants.

n Waste with TDS can be handled.

n Energy integration is possible via Gas turbine andhydraulic turbine.

n Very less space, even it can be underground.

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§ Lower operating cost.

§ Valuable low molecular weight acids such as aceticacid could be produced.

§ When used as pretreatment to anaerobic bio process,§higher yields of CH4 (say 30-40 %) possible.

§ Total mineralization of the waste is possible.

§ Treated water can be recycled / reused.

WATER CONSERVATION (WATCON) is possible

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Limitations:

Ø Capital intensive due to exotic MOC (often “titanium”).

How to cope?

Lining or cladding will help! (only wetted parts)

Ø To reduce volume of the waste, membranes can be used upstreambe used upstream

Ø The residence time can be reduced by using bio treatment at downstream. MBR for water recycle.

However, depreciation benefit makes it

attractive!

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Compressed airEffluent

AQUEOUS STREAM for Water Recovery

Product Gas

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Recovery

Heat transfer Fluid

Wet Air Oxidation: Schematic Diagram

v SONI WO Sonication - Wet Oxidation

v WO MEM Wet Oxidation- Membrane

HYBRID PROCESSES

v MEM WO Membrane - Wet Oxidation

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A SYSTEMATIC APPROACH FOR WATER TREATMENT for

RECYCLE

We can use following guidelines for water recycle in 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

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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 a 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.

• 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

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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 techno - economic feasibility study to ensure that set goals or targets could be achieved / realized.

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• Implement the project without any delays.

WATER MANAGEMENT IS MUST for

SUSTAINABLE DEVELOPMENT

Recommended Readings :

v Wet air oxidation. Mishra, V. S.; Mahajani, V. V.; Joshi, J. B. Ind. Eng. Chem. Res. 1995, 34, 2.

v A novel way to treat refractory waste: Sonication followed by Wet Oxidation(SONIWO)by Wet Oxidation(SONIWO)Ingle, M. N.; Mahajani, V.V.; Journal of Chemical Technology Biotechnology. 1995, 64, 80.

v Studies in treatment of disperse dye waste : membrane-wet oxidation process. Dhale A. D.; Mahajani, V. V. ; Waste Mgmt. 2000, 20, 85.

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Interactive Session Begins now

INNOVATION IS ANYTHING THAT PRODUCES MONEY

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