4.Physicochemical and Biological Treatment Processes

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Introduction

Physicochemical Processes

Air Stripping

Carbon Adsorption

Stream Stripping

Chemical Oxidation

Membrane Process

(Types, Principles, Equipment Used & ApplicationRanges)

Biological Method Ex Situ System

In Situ System

Comparisons Of Different Treatment Facilities


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Air Stripping

Carbon Adsorption

Stream Stripping

Chemical Oxidation

Membrane Process


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Mass transfer process

enhance the volatilization of compounds

from liquid phase into vapor phase (air)by actively passing air through water.

Cost effective unit for removing VOCs fromcontaminated water.

Performed by using stripping basins orstripping tower.

AIR

STRI

PPING


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PACKED TOWER AIR STRIPPER

Frequently used for

remediating groundwater

Summary: The process consists of

countercurrent flow of air and

contaminated groundwater

through a vertical column

packed with spherically shaped

pieces, which improve the

effective surface area for mass

transfer and ensure

homogeneity of the mass

transfer system.

AIR

STRI

PPING


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Two-phase resistance or two-film theory used

for description of mass transfer in the gas-

liquid exchange process.

The transfer of VOCs from

water to air consists of

transfer from:

Bulk liquid to liquid film Liquid film to air film

Air film to bulk air

AIR

STRI

PPING


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The parameter include: Column diameter (typically 0.5 3.0 m)

Height (1 to 15 m)

Air-to-water ratio ( as low as 5 to several hundred,controlled by flooding and pressure drop considerations)

Type Size of packaging

Designed to meet all of the performance constraints: Required removal amounts

Allowable pressure drop

Operating & construction costs The construction costs are closely related to the tower

dimensions Capital cost being a function of tower volume

Operation costs increase with column height

AIR

STRI

PPING


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Activated carbon removes impurities fromfluids (liquid or gas) by a process called

adsorption.

Adsorption is a surface phenomenon that

results in the accumulation of molecules onthe surface of the internal pores of an

activated carbon.

This occurs in pores slightly larger than the

molecules that are being adsorbed, which iswhy it is very important to match the pore

size of the activated carbon with the

molecules you are trying to adsorb.

CARBONADSORPTIO

N


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CARBONADSORPTIO

N


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Contaminated

water enter the

top of column

contacted withcarbon exit

through an

underline systemat the bottom


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Air scouring & backwashing to avoid the

buildup of head loss due to the accumulation

of solid particles present in the influent

Spent removalfor generation and theaddition of new carbon

Continuous flow column

Other modification process:

Downflow in series

Downflow in parallel

Upflow expanded in series

Moving bed


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Solubility Less soluble compounds are adsorbed to a

greater extent than more soluble compounds

Molecular structure Branch chain organics are more easily adsorbed

than straight-chain organics

Molecular weight Larger molecules are generally more easily

adsorbed than smaller molecules Polarity Less polar (or weakly ionized) organics are more

easily adsorbed than polar (or strongly ionized)organics


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Objective: to detoxify waste by adding an

oxidizing agent to chemically

transform waste components.

Capable of destroying a wide range oforganics molecules (chlorinate VOCs,

phenols, etc)

Oxidizing agents is added to oxidize the

waste component of concern-serve as the

reducing agents.


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Oxidizing agents are:

Non specific

Will react with any reducing agents

present in the waste streamTypically applied to liquid hazardous

waste.

Well established technologymost economical when organics

other than ones of concern are inlow concentration.


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More complex process design techniques

Is utilized for the removal of volatile and

sometimes semivolatile compounds from

groundwater or wastewaterCapable in reducing VOC to very low

concentration

Based on the transfer of organic from liquid

to gas phase


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Steam, rather than air, is used as thestripping gas

The stripping gas, steam, is infinitely solublein liquid phase, water

Steam strippers operate at much highertemperatures than air strippers.

The organics in the water may be recoveredas a separate liquid gasses


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ATMOSPHERIC PRESSURE STEAM STRIPPING COLUMN


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Operate at a temperature that is slightly

higher than normal boiling point of water (215

to 220F).

Contaminated water enter at feed point.At elevated temperature the

organics vaporize transfer from

liquid to gas phase concentration of

organics increase in the stripping stream.The steam exits the top of the column where it

undergoes a phase change to a liquid in the

condenser.


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VACUUM STEAM STRIPPER


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The steam is compressed to an elevated

pressure that will cause the gas to condense

to a liquid.

Use mechanical compression to creates avacuum on the compressor inlet side, creates

vacuum condition in the steam stripper.

The overhead mixture is decanted into

separate organic and aqueous phases. The aqueous phase is returned to the top of

the stripping column as in atmospheric

stripper.


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To separate water from contaminants.

Well established technology in industry.

MEMBRANE-usually refers to a barrier to flow

that will allow the passage of water, ions, or

small molecules.

Do not operate as a conventional filtration

process.


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The application generally limited to those

instances where extremely toxic materials

cannot be removed by more cost effective

technologies.

Three membrane process of interest in

managing hazardous waste: Electrodialysis

Reverse osmosis

ultrafiltration


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Consist of the separation of ionic species byapplying a direct-current electrical field.

Used in the electroplating industry for therecycling of metals and purified water.

Usually removes only 30-60 percent of themetals.

Brine water is return to the planting bath,treated water is returned to the rinsedtanks.


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A solvent is separated from a solution by

applying a pressure greater than the osmosis

pressure, thus forcing the solvent through a

semipermeable membrane.

Consist of several modules to which the feed

is added through a high-pressure pump.

Is used in the electroplating industry to

recover both metals and water,


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Can be applied to both organics and

inorganic hazardous waste problems.

Important RO design consideration: The need to dispose

Recycle, or reuse both the permeate

Stream concentration


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Separates solutes from a solvent on the basisof molecular size and shape by passingthrough a membrane module.

Water and small molecules move through themembrane to the lower-pressure side, whilelarger molecules are retained by themembrane.

Solutes of molecular weight greater thanabout 500 and less than 500,000 can beseparated from a solution.


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is a variety of membrane filtration in whichhydrostatic pressure forces a liquid against asemipermeable membrane.

Suspended solids and solutes of high molecularweight are retained, while water and lowmolecular weight solutes pass through themembrane.

This separation process is used in industry andresearch for purifying and concentratingmacromolecular solutions, especially proteinsolutions.


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Ex-situ System

In-situ System


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Treatment of liquid

Slurry-phase treatment

Solid-Phase and Vapor-Phase Treatment

Monitored Natural Attenuation


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TREATMENT OF LIQUIDSCan treat using bioreactor design such as

batch reactor, standard activated sludge

system, fluidized beds, membrane system,etc.

Consist of passing the contaminated liquidthrough a reactor containing suspended oracclimated microorganisms.

Flow-continuous or batch.

Reactor-operate under aerobic or anaerobicconditions.


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Major factor to consider in used of liquid-

phase system:

Mixing regime

Hydraulic retention time

Solid retention time

Total dissolved solids

others


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SLURRY-PHASE TREATMENT Involve the treatment of contaminated

soils/sludges mixed with clean or

contaminated liquids. Potential process for biodegrading difficult-

to-treat soils~high level of heavy oils,pesticides,etc.

Success~ aggressive mixing and treatment.High cost~excavation, materials handling,

residuals handling

Rarely used


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SLURRY-PHASE TREATMENT Similar to conventional suspended growth

biological treatment.

Fundamental treatment:

Mixing/aeration

Desorption

Biodegardation

Flow- continuous or batch


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SOLID-PHASE AND VAPOR-PHASE TREATMENT

Include a broad class of biological methods used

to treat contaminated soils and sludges

containing minimal free moisture.

Three major process:

Land treatment

Composting Soil piles


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MONITORED NATURAL ATTENUATION

Meaning~ in its original place.

In-situ bioremediation~ method of treating

subsurface contaminants where they are found

without excavating the overlying soil.

Effective system.


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MONITORED NATURAL ATTENUATION

Being used at site with wide range of

contaminants.

Is a remediation approach that involves

quantifying, evaluating and monitoring the

natural process ~ reduce concentration ofcontaminants.


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4.Physicochemical and Biological Treatment Processes

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