Advanced Waste Water Treament

Advanced wastewater treatment Gyeongsang National University Department of Biological and chemical Engineering Environmental Engineering Lab Ngoc Thuan Le

Need for advanced wastewater treatment 1.

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

2.

Remove TSS for more effective disinfection.

3.

Remove nutrients contained to limit eutrophication of sensitive water bodies.

4.

Remove specific inorganic (e.g., heavy metals) and organic constituents (e.g., MTBE) to meet more stringent discharge and reuse requirements both surface water and land-based effluent dispersal and for indirect potable 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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1.

3.

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 Removal of dissolved inorganic constituents (ammonia, nitrate, nitrite, phosphorus, total dissolved solids) • Chemical precipitation • Ion exchange • Ultrafiltration • Reverse osmosis • Electrodialysis • Distillation 5

4.

Removal of biological constituents (bacteria, protozoan cysts and oocysts, viruses) • Depth filtration • Micro and ultrafiltration • Reverse osmosis • Electrodialysis • Distillation

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

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Introduction to depth filtration

• Grain size is the principal filter medium characteristic that affects the filtration operation

a.

Flow during filtration cycle

b.

Flow during backwash cycle

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Particle removal mechanisms

a.

By straining

a.

By adhesion

b.

By sedimentation or inertial impaction

b.

By flocculation

c.

By interception

Other phenomena: chemical/physical adsorption or biological growth 8

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 monomedium downflow filter

b. Conventional dualmedium downflow filter

e. Pulse-bed filter

c. Conventional mono-medium deep-bed downflow filter

d. Continuous backwash deepbed upflow 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 minimize clogging A smaller sand size is used in the second filter to remove residual particles from the first stage filter 12

Effluent filtration with chemical addition

•

To achieve specific treatment objectives including removal of specific contaminants • 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 materials Surface filters have openings in size range from 10 to 30µm. In membrane filters the pore size can vary from 0.0001 to 1.0µm

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Membrane filtration Membrance process

Membrane driving force

Typical separation mechanism

Operating structure (pore size)

Typical operating range, µm

Permeate description

Typical constituents removed

Microfiltration

Hydrostatic pressure difference

sieve

Macropore s (>50nm)

0.08-2.0

Water+dissolved solutes

TSS, turbidity, protozoan, some bacteria and viruses

Ultrafiltration

Hydrostatic pressure difference

sieve

Mesopores (2-50nm)

0.005-0.2

Water+small molecules

Macromolecules, colloids, most bacteria, some viruses, protein

Nanofiltration

Hydrostatic pressure difference

sieve+solution/diff usion+exclusion

Micropores (<2nm)

0.001-0.01

Water+very small molecules, ionic solutes

Small molecules, some harness, viruses

Reverse osmosis

Hydrostatic pressure difference

solution/diffusion +exclusion

Dense (<2nm)

0.00010.001

Water+very small molecules, ionic solutes

very small molecules, color hardness, sulfates, nitrate, sodium, other ions

Dialysis

Concentration difference

Diffusion

Mesopores (2-50nm)

_

Water+very small molecules,

Macromolecules, colloids, most bacteria, some viruses, protein

Electrodialysis

Electromotive force

ion exchange with selective membranes

Micropores (<2nm)

_

Water, ionic solutes

ionized salt ions

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

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Reverse osmosis (RO) • When two solutions having different solute concentrations are separated by a semi permeable membrane, a difference in chemical potential will exist across the membrane • RO is used for the removal of dissolved constituents from the wastewater remaining after advanced treatment with depth filtration of microfiltration.

a.

Osmotic flow

b.

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 Faraday’s Laws of electrolysis

I=

FQNŋ nEc

Where: I = current, amp F = Faraday’s constant = 96,485amp.s/gram equivalent = 96,485 A.s/eq n = number of cell in the stack Ec = current efficiency expressed as a fraction

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Adsorption •

Adsorption is 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

Total surface area Bulk density

Type of activated carbon GAC

PAC

m2/g

700-1300

800-1800

kg/m3

400-500

360-740

kg/l

1.0-1.5

1.3-1.4

mm (µm)

0.1-2.36

(5-50)

Effective size

mm

0.6-0.9

na

Uniformity coefficient

UC

≤1.9

na

Â

16-30

20-40

600-1100

800-1200

minimum

75-85

70-80

Ash

%

≤8

≤6

Moisture as packed

%

2-8

3-10

Particle density, wetted in water Particle size range

Mean pore radius Iodine number Abrasion number

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Fundamentals of adsorption • Absorbent phase concentration data

(C 0 −C e )V qe = m Where: qe= absorbent (solids) phase concentration after equilibrium, mg adsorbate/g adsorbent Co = initial concentration of adsorbate, mg/L Ce = final equilibrium concentration of adsorbate after absorption has occurred, mg/L V = volume of liquid in the reactor, L m = mass of absorbent, g

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Types of activated carbon contactors

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Gas stripping •

Gas stripping involves 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)

Typical water and airflow patterns for gas stripping towers

Countercurrent flow

Cross flow Current flow

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Typical stripping towers for the removal of volatile gases from water

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ION EXCHANGE

•

Ion exchange is a unit process in which ions of a given species are displaced from an insoluble 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 cation 2. Weak-acid cation 3. Strong-base anion 4. Weak-base anion 5. Heavy-metal selective chelating resins

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Typical ion-exchange reaction • For natural zeolite (Z) Ca2+ ZNa+ + Mg2+ Fe2+

Ca2+ Z Mg2+ + 2Na+ Fe2+

• For synthetic resin (R) Strong acid cation exchange: RSO3H + Na+ 2RSO3Na + Ca+2

RSO3Na + H+ (RSO3)2Ca + 2Na+

Weak acid cation exchange: RCOOH + Na+ 2RCOONa + Ca+2

RCOONa + H+ (RCOO)2Ca + 2Na+

Strong-base anion exchange: RR’3NOH + ClWeak-base anion exchange: RNH3OH + Cl2RNH3Cl + SO42-

RR’3NCl + OHRNH3Cl + OH(RNH3)2SO4 + 2Cl24

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 complete demineralization of water

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Chemical oxidation

•

Oxidizing agents:  ozone (O3),  hydrogen peroxide (H2O2),  permanganate (MnO4),  chloride dioxide (ClO2),  chlorine (Cl2) or (HClO) and  oxygen (O2)

•

For reduction of:  BOD,  COD,  ammonia,  nonbiodegradable organic compounds. 27

•

Phosphate precipitation with aluminum and iron Al3+ + HnPO43-n AlPO4 + nH Fe3+ + HnPO43-n

FePO4 + 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 •

Distillation is a unit operation in which the components of a liquid solution are separated by vaporization and condensation.

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Thank you for your attention!

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