13200148 Advanced Waste Water Treament

8/2/2019 13200148 Advanced Waste Water Treament

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Advanced wastewater treatment

Gyeongsang National UniversityDepartment of Biological and chemical EngineeringEnvironmental Engineering Lab

Ngoc Thuan Le


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Need for advanced wastewater treatment

1. Remove organic matter and TSS to meet more stringent discharge andreuse requirements.

2. Remove TSS for more effective disinfection.

3. Remove nutrients contained to limit eutrophication of sensitive waterbodies.

4. Remove specific inorganic (e.g., heavy metals) and organic constituents(e.g., MTBE) to meet more stringent discharge and reuse requirementsboth surface water and land-based effluent dispersal and for indirectpotable reuse application.

5. Remove specific inorganic and inorganic constituents for industrial reuse(e.g., cooling water, process water).


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Technologies used for advanced treatment

1. Removal of organic and inorganic colloidal and suspended solids(suspended solids, organic matters), using filtration

Depth filtration Surface filtration Membrane filtratration


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Depth filtration Surface filtration


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2. Removal of dissolved organic constituents (total organic carbon,refractory organic, volatile organic compounds)

Carbon adsorption Reverse osmosis Chemical precipitation Chemical oxidation Advanced chemical oxidation Electrodialysis Distillation

3. Removal of dissolved inorganic constituents (ammonia, nitrate, nitrite,phosphorus, total dissolved solids)

Chemical precipitation Ion exchange Ultrafiltration Reverse osmosis Electrodialysis Distillation


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4. Removal of biological constituents (bacteria, protozoan cysts andoocysts, viruses)

Depth filtration Micro and ultrafiltration Reverse osmosis Electrodialysis

Distillation

Because the effectiveness of the unit operations and processes listed isvariable, disinfection of the treated effluent is required for most

application


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Introduction to depth filtration

a. Flow during filtration cycleb. Flow during backwash cycle

Grain size is the principal filter mediumcharacteristic that affects the filtrationoperation


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Particle removal mechanisms

a. By strainingb. By sedimentation or inertial impactionc. By interception

d. By adhesione. By flocculation

Other phenomena: chemical/physical adsorption or biological growth


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Selection and design considerations for depth filters

1. Selection and design filter technologies must be based on: Knowledge of the types of filters that are available A general understanding of their performance characteristics An appreciation of the process variables controlling depth filtration

2. Design for effluent filtration systems include: Influent wastewater characteristics Design and operation of the biological treatment process Type of filtration technology to be used Available flow-control options Type of filter backwashing system Filter control systems and intrumentation


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Available filtration technologies

a. Conventional mono-mediumdownflow filter b. Conventional dual-mediumdownflow filter c. Conventional mono-mediumdeep-bed downflow filter

d. Continuous backwash deep-bedupflow filter

e. Pulse-bed filter f. Traveling-bridge filter


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Synthetic-medium filter High pressure filter

Slow sand filter


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Two-stage filtration

A large size sand diameter is used in the first filter to increase the contact time and to minimizecloggingA smaller sand size is used in the second filter to remove residual particles from the first stage filter


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Effluent filtration with chemical addition

To achieve specific treatment objectives including removal of specificcontaminants

Phosphorus Metal ions

Humic substances

Chemicals commonly used in effluent filtration Organic polymers (cationic, anionic, or nonionic (no charge) Alum and ferric compounds (chloride)


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Surface filtration

Materials: woven metal fabrics, cloth fabrics of different weaves, and variety of synthetic materialsSurface filters have openings in size range from 10 to 30m. In membrane filters the pore size can varyfrom 0.0001 to 1.0m


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Membrane filtration

Materials: different organic or inorganic materials: polypropylene, cellulose acetate, aromatic polyamides,and thin film composite (TFC).

Membranceprocess

Membranedriving force

Typicalseparationmechanism

Operatingstructure(pore size)

Typicaloperatingrange, m

Permeatedescription

Typical constituentsremoved

Microfiltration Hydrostaticpressure difference sieve Macropores (>50nm) 0.08-2.0 Water+dissolvedsolutes TSS, turbidity, protozoan,some bacteria and viruses

Ultrafiltration Hydrostaticpressure difference

sieve Mesopores(2-50nm)

0.005-0.2 Water+smallmolecules

Macromolecules, colloids,most bacteria, someviruses, protein

Nanofiltration Hydrostaticpressure difference

sieve+solution/diffusion+exclusion

Micropores(


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Reverse osmosis (RO)

When two solutions having different solute concentrations are separated by a semipermeable membrane, a difference in chemical potential will exist across themembrane

RO is used for the removal of dissolved constituents from the wastewater remainingafter advanced treatment with depth filtration of microfiltration.

a. Osmotic flowb. Osmotic equilibrium

c. Reverse osmosis


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Electrodialysis (ED) In the electrodialysis process, ionic components of a solution are separated through the use of

semipereable ion-selective membrane The current required for electrodialysis can be estimated by Faradays Laws of electrolysis

Where:I = current, ampF = Faradays constant

= 96,485amp.s/gram equivalent = 96,485A.s/eq

n = number of cell in the stackEc = current efficiency expressed as a

fraction

nEc

FQN I


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Adsorption

Adsorptionis the process of accumulation substances that are in solution on a suitable interface

Types of adsorbents: activated carbon, synthetic polymeric, and silica-based adsorbents Activated carbon: (1)powdered activated carbon (PAC), a diameter of less than 0.074mm (200

sieve), and (2)granular activated carbon (GAC), a diameter greater than 0.1mm (140 sieve)

Parameter Unit Type of activated carbon

GAC PAC

Total surface area m2 /g 700-1300 800-1800

Bulk density kg/m3 400-500 360-740

Particle density, wetted in water kg/l 1.0-1.5 1.3-1.4

Particle size range mm (m) 0.1-2.36 (5-50)

Effective size mm 0.6-0.9 na

Uniformity coefficient UC 1.9 na

Mean pore radius 16-30 20-40

Iodine number 600-1100 800-1200

Abrasion number minimum 75-85 70-80

Ash % 8 6

Moisture as packed % 2-8 3-10


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Fundamentals of adsorption Absorbent phase concentration data

Where:q e = absorbent (solids) phase concentration

after equilibrium, mg adsorbate/gadsorbent

C o = initial concentration of adsorbate, mg/LC e = final equilibrium concentration of

adsorbate after absorption hasoccurred, mg/L

V = volume of liquid in the reactor, Lm = mass of absorbent, g

m

V C C q ee

)( 0


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Types of activated carbon contactors


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Gas stripping

Gas strippinginvolves the mass transfer of a gas from the liquid phase to the gas phase.

Considerable attention: remove ammonia, odorous gases and volatile organic compounds (VOCs)

Countercurrent flow Current flowCross flow

Typical water and airflow patterns for gas stripping towers


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Typical stripping towers for the removal of volatile gases from water


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ION EXCHANGE

Ion exchangeis a unit process in which ions of a given species are displaced from aninsoluble exchange material by ions of a different species in solution. Domestic water softening: where sodium ions from a cationic-exchange resin replace

the calcium and magnesium ions in the treated water. Ion exchange has been used in wastewater application for removal of nitrogen, heavy

metals, and total dissolved solids

Ion-exchange materials: Naturally, zeolites (complex of aluminosilicates with sodium) Synthetic ion-exchange material: resins or phenolic polymers

1. Strong-acid cation2. Weak-acid cation3. Strong-base anion4. Weak-base anion5. Heavy-metal selective chelating resins


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Typical ion-exchange reaction For natural zeolite (Z)

Ca2+ Ca2+ZNa+ + Mg2+ Z Mg2+ + 2Na+

Fe2+ Fe2+

For synthetic resin (R)

Strong acid cation exchange:RSO3H + Na+ RSO3Na + H+2RSO3Na + Ca+2 (RSO3)2Ca + 2Na+

Weak acid cation exchange:

RCOOH + Na+ RCOONa + H+

2RCOONa + Ca+2 (RCOO)2Ca + 2Na+Strong-base anion exchange:

RR3NOH + Cl- RR3NCl + OH-Weak-base anion exchange:

RNH3OH + Cl- RNH3Cl + OH-2RNH3Cl + SO42- (RNH3)2SO4 + 2Cl-


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Application of ion-exchange

Typical flow diagram for the removal of ammonia by zeolite exchange


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Application of ion-exchange

Typical flow diagram for the removal of hardness and for the completedemineralization of water


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Oxidizing agents:

ozone (O3),

hydrogen peroxide (H 2O2),

permanganate (MnO 4),

chloride dioxide (ClO 2),

chlorine (Cl 2) or (HClO) andoxygen (O 2)

For reduction of:

BOD,

COD,ammonia,

nonbiodegradable organic compounds.

Chemical oxidation


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Phosphate precipitation with aluminum and iron

Al 3+ + H nPO 43-n AlPO 4 + nH

Fe3+ + H nPO 43-n FePO 4 + nH

There are many competing reactions because of the effects of alkalinity, pH,trace elements, and ligands in wastewater

Dosages are established of bench scale test and occasionally by full scale tests.


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Ozone/Hydrogen peroxide

H2O2 + 2O3 HO* + HO* +3O2


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DISTILLATION

Distillationis a unit operation in which the components of a liquid solution are separated byvaporization and condensation.


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Thank you for your attention!

13200148 Advanced Waste Water Treament

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