CHAPT 3-Water Supply (1)

CHAPTER 3

WATER SUPPLY

BFC 3103ENVIRONMENTAL ENGINEERING

CONTENT Introduction Water quantity requirement Intake of raw water Screens and grit removal Treatment process:

(i) flocculation and coagulation(ii) softening

(iii) sedimentation (iv) filtration (v) disinfection.


INTRODUCTION


Sources of water and issues related with the sources

SOURCES OF WATER

ISSUES

Surface water High flows, easy to contaminate, relatively high SS, TURBIDITY and PATHOGENS. In some part, rivers and streams dry up during the dry season

Groundwater Lower flows but natural filtering capacity that removes SS, turbidity and pathogens. May be high in TDS, including Fe, Ca and Mg (hardness). Difficult to clean up after contaminated. Renewal times can be very long

Seawater Energy intensive to desalinate, so costly compared with other sources. Desalination can occur by distillation and reverse osmosis

Reclaimed and reuse water

Technically feasible. Currently used for irrigating cultural crops, landscaping, groundwater recharge and potable water

TREATMENT PROCESSES


Water Treatment Processes

Sedimentation Filtration Membrane: RO,

Ultra-filtration, Micro-filtration

Adsorption: GAC, Powder AC

Electrodialysis, Distillation, Aerogel

PHYSICAL BIOLOGICAL CHEMICAL

*Coagulation/Flocculation*Chemical precipitation*Chlorination*UV*Ozonation

**Not normally used in water treatment*Biological filter*Fluidized bed biological reactor*Bioden, Autotrophic sulfur process, Daisy wheel in- situ system


Classes of water treatment

Class Description Source

A No treatment Some borehole waterOccasional upland water

B Disinfection only Some borehole waterOccasional upland water

C Standard water treatment Lowland rivers & reservoir

D Special treatment Some rural supplies (Fe & Mn)Color removalTrace element removalIndustrial waterElectronic industry requirementAlgae removalOrganic removal

Unit processes in different raw water classes

Intake Intake Intake

Pre-treatment

Primary treatment

Secondary treatment

Disinfection

Advanced treatment

Fluoridation

Groundwater supply Class B

Standard water treatment Class C

Special water treatment Class D

Aeration

Disinfection Disinfection Disinfection

Coarse screeningFine screening PumpingStorageEqualizationNeutralization AerationChemical pre-treatment

ScreeningPumpingStorageEqualizationNeutralization AerationSoftening Chemical pre-treatment

Coagulation & mixingFlocculationSedimentation

Filtration

Coagulation & mixingFlocculationSedimentation

Filtration

Adsorption Activated carbonMembrane processesFe & Mn removalHaloganated compounds removal

Fluoridation Fluoridation Fluoridation

Treatment categorization

Concentration of major constituents found in water

General classification Specific constituents Typical concentration range

Major inorganic constituents

Ca2+, Cl-, F-, Fe2+, Mn2+,NO3-, Na2+,

SO4-2,

1- 1000 mg/L

Minor inorganic constituents

Cadmium, chromium, copper, lead, mercury, nickel, zinc, arsenic

0.1-10μg/L

Naturally occuring organic compounds

Naturally occuring organic matter (NOM) that is measured as total organic carbon (TOC)

0.1-20μg/L

Anthropogenic organic constituents

Synthetic organic chemicals (SOC) and emerging chemicals of concern used in industry, household and agriculture (eg:benzene)

Below 1 μg/L and ups to the tens of mg/L

Living organism Bacteria, algae, viruses millions


Forms of impurities

Raw water may contain impurities in several forms including: Particulates (size >10-1 mm) – dust Suspended ( 10-3 mm <size<10-1 mm) – turbidity Colloidal (10-6 mm <size,10-3 mm) – clay minerals Dissolved (size < 10-6 mm) – humic/tannic acid,

colour

Objective of the water industry to reduce these impurities to acceptable levels.

Unit processes that remove a significant amount of raw-water constituents

Constituent Unit Process (es)

Turbidity and particles

Coagulation/flocculation, sedimentation, granular filtration

Major dissolved

inorganics

Softening, aeration, membranes

Minor dissolved inorganics

Membranes

Pathogens Sedimentation, filtration, disinfection


Types of particles settling encountered during drinking water and waste water

treatmentTypes of settling

Description Where used in treatment process

Type 1 Particles settle discretely at a constant settling velocity

Grit removal

Type 2 Particles flocculate during settling due to velocity gradient of fluids or differences in the settling velocities of particles. Their size is increasing, and they settle faster as time passes

Coagulant processes and most conventional sedimentation basin

Type 3 Blanket of particles is formed at high particle concentrations (above 1000 mg/L), and a clear interface is observed between the blanket and clarified water above it

Lime-softening sedimentation and in wastewater sedimentation and sludge thickeners

Motivation for the Use of Coagulation in water Treatment Water/wastewater often contain pollutants that are present is

colloidal form· In such cases the colloidal suspension may contain:

organic materials metal oxides insoluble toxic compounds stable emulsions insoluble toxic compounds material producing turbidity

This material must be removed prior to discharge Because of the nature of the colloidal suspension these

particles will not sediment or be separated with conventional physical methods (such as filtration or settling) unless they are agglomerated through coagulation

(i) coagulation/flocculationObjective: to turn the small particles of color,

turbidity and bacteria into large flocs, either as percipitates or suspended particles.

Technically: coagulation applies to the removal of colloidal particles. However,the term has been applied more loosely to removal of dissolved ions, which is actually percipitation. THUS…

Coagulation as a method to alter the colloids so that they wil be able to approach and adhere to each

other to form larger floc particles

continues..

WHY COLLOIDS ARE SUSPENDED IN SOLUTION AND CAN’T BE REMOVED BY SEDIMENTATION AND FILTRATION???

It’s because

The particles in colloid (0.1-20 m)range are too fine to settle in a reasonable time period and too SMALL to be

trapped in the pores of the filter


continues…

Most colloids are stable becoz they posses a negative charge that repels other colloidal particles before they collide with one another.

The colloids are continually involved in Brownian movement

How to destabilize the particles???

NEUTRALIZE THE CHARGE OF COLLOIDALPARTICLES BY ADDITION OF AN ION

OPPOSITE TO IT

Na+ willreduce

the charge

The higherthe [Na+ ], the

LOWER the charge,therefore the LOWERthe repelling forces


continues…

PURPOSE OF COAGULATION

(i) To alter the colloids so that they can adhere to each other

(ii) During coagulation, a positive ion is added to the water to REDUCE the surface charge to the point where the colloids are not repelled from each other

(iii) A coagulant is the substance (chemical) that is added to the water to accomplish coagulation


continues…

COAGULANT:- is the substance (chemical) that is added to the water

to destabilize particles and accomplish coagulation

PROPERTIES OF COAGULANT Trivalent cations (Al3+, Fe3+) Nontoxic: obvious for the production of safe water Insoluble in the neutral pH. The coagulant that is

added must percipitate out of solution so that high concentration of the ion are not left in the water. Such precipitation greatly influenced the colloidal removal process


continues…

Types of coagulant commonly used

Coagulant type examples

Inorganic metallic coagulant

Aluminium sulfate (Al2(SO4)3•14H2O, sodium aluminate, aluminium chloride, ferric sulfate and ferric chloride

Prehydrolyzed metal salts

Made from alum and iron salts and hydroxide under controlled condition; polyaluminium chloride (PAC)

Organic polymers Cationic polymers, anionic polymers, and nonionic polymers

Natural plant-based materials

Opuntia spp. And Moringa Oleifera (used in many parts of the world esp. developing country.


continues… Aluminium..

(i) Common coagulant used

(ii) Can be purchased as dry/ liquid alum

(iii) Has an average molecular weight of 594

(iv) When alum is added to a water containing alkalinity, the reaction will occur

Al2(SO4)3•14H2O + 6HCO3-↔2Al(OH) 3• 3H2O(s) + 6CO2 +8H2O + 3SO4

2-

1 mole of alum added uses 6 moles of alkalinity and produces 6 moles of CO2


continues…

The above reaction shifts the carbonate equilibrium and decreases the pH

However, as long as sufficient alkalinity is present and CO2 (g) is allowed to evolve, the pH is not drastically reduced and is generally not an operational problem

When sufficient alkalinity is not present to neutralize the sulfuric acid production, the pH may greatly reduced

2 important FACTORS in

coagulantaddition:1) pH

2) dose


continues….

One of the most important to evaluate coagulation efficiency is to conduct jar test.

Try these QUESTIONS 1)Two sets o such jar test were conducted on

a raw water containing 15 NTU and an HCO3-

alkalinity concentration of 50 mg/L expressed as CaCO3. Given the data, find the optimal pH, coagulant dose and the theoretical amount of alkalinity that would be consumed at the optimal dose


Continues..

Jar Test 2-------------------------------------------------------------------------------------------

1 2 3 4 5 6

pH 6.0 6.0 6.0 6.0 6.0 6.0Alum dose 5 7 10 12 15 20SettledTurbidity 15 10.5 6 5.5 7 13-----------------------------------------------------------------------------------------------

Jar Test 1-------------------------------------------------------------------------------------------

1 2 3 4 5 6

pH 5.0 5.5 6.0 6.5 7.0 7.5Alum dose 10 10 10 10 10 10SettledTurbidity 10.5 7 6.5 5.7 9 13-----------------------------------------------------------------------------------------------


solution

Results of jar test

Cont..

The optimal pH was chosen as 6.25 The optimal alum dose was about 12.5 mg/L

1 mole of alum consumes 6 mole of alkalinity (HCO3

-).

To calculate moles of alum added per liter, using the following equation

Al2(SO4)3•14H2O + 6HCO3-↔2Al(OH) 3• 3H2O(s) + 6CO2 +8H2O + 3SO4

2-

Cont..

Mg/L = molarity x molecular wt x 103

= (moles/L) x (g/mole) x 103 mg/g)

12.5 mg/L alum, MW of alum= 594 g/mole

mole/L = 12.5 x 10-3 g/L (alum)/594 g/mole

= 2.1 x 10-5 moles/L

Which will consume 6 (2.1 x 10-5 ) = 1.26 x 10-4 M HCO3

-

Cont..

MW HCO3- = 61, so

(1.26 x 10-4 moles/L)(61 g/mole)(103 mg/g) = 7.7 mg/L HCO3- are

consume, mg/L as CaCO3 = 7.7 (50)/61 = 6.31 mg/L HCO3

- as CaCO3

Continues..2) Jar testing was performed using alum on a raw drinking-

water source that contained an initial turbidity of 20 NTU and alkalinity of 35 mg/L as CaCO3. The optimum coagulant dosage was determined as 18 mg/L with final turbidity of 0.25 NTU. Determine the quantity of alkalinity consumed as CaCO3.

3) Jar test were performed on untreated river water. An optimum dose of 12.5 mg/L of alum was determined. Determine the amount of natural alkalinity (mg/L as CaCO3) consumed. If 50 x 10^6 gal./day of raw water are to be treated, determine the amount of alum required (kg/year)


(ii) Softening (hardness removal)

Hardness: the sum of all polyvalent cations. The common units of expression are mg/L as CaCO3.

Hardness: is used to characterize a water that does not lather well, causes a scum in the bath tube and leaves hard, white, crusty deposits on coffee pot, tea kettles and hot water heaters.

Water hardness: caused by divalent cations, primarily calcium and magnesium ions(Ca2+ and Mg2+)

How the water becomes hard???


continues.. Refer to Fig 4.14 in the text book TOTAL HARDNESS:

When associated with alkalinity anion (eg: HCO3- , the

hardness is defined as carbonate hardness. Often called temporary hardness heating the water removes it

When associated with non alkalinity anion(eg: SO4- the

hardness is defined as noncarbonated hardness.called permanent hardness becoz it is not removed when heating

TH = CH + NCH

CARBONATE

NONCARBONATE


continues….

The relationship between TH, CH and NCH (please refer Fig 4.16 text book)

Calculation (eg)

A water has an alkalinity of 180 mg/L as CaCO3. the Ca2+ concentration is 155 mg/L and the Mg2+concentration is 42 mg/L as the ion.

The pH is 8.1.Find the total, carbonate and

noncarbonate hardness


continues…

Hardwater classification-----------------------------------------------------------------------------------------Hardness range description(mg/L CaCO3. ) --------------------------------------------------------------------------------0 -75 soft75 -100 moderately hard100-300 hard300 very hard-------------------------------------------------------------------------------------• A water treatment goal is to provide water with a hardness in the range of

75 – 120 mg/L as CaCO3

HOW??? by Lime-Soda SOFTENING

treatment

continues….

Lime-Soda Softening

-hardness precipitation is based on the following two solubility reaction:

Ca2++CO32-↔CaCO3

Objective: to precipitate calcium asCaCO3 (s) .In order to precipitate,

the water must pH 10.3

Mg2++2OH-↔MgOH2

In order to precipitate Mg(OH)2(s),The water must pH 11

to precipitate the Ca2+ as CaCO3 & Mg2+ as Mg(OH)2

to precipitate the Ca2+ as CaCO3 & Mg2+ as Mg(OH)2

Eq 1 Eq 2

Cont..

In softening process – increase the concentration of CO3

2- and /or OH- by addition of chemicals. – drive the reactions in Eq 1 & 2 to the right.

Natural occurring alkalinity (HCO3-) is converted to

carbonate (CO32- ) as much as possible by addition of

hydroxyl ions (OH-). Hydroxyl ions cause the carbonate buffer system to shift

to the right, thus provide the carbonate for the precipitation reaction. (buffer solution – a solution that resist large changes in pH when acid/based is added or when the solution is diluted).

Cont..

Common source of hydroxyl ions is calcium hydroxide [Ca(OH)2] – hydrated lime.

Quicklime (CaO) is more economical than hydrated lime– preferable in many water treatment plant (WTP).

Quicklime is converted at the WTP by mixing CaO and H2O – produce slurry Ca(OH)2 (slaking process)

To supply carbonate ions – add sodium carbonate (Na2CO3) – soda ash or soda.

CaO + H2O Ca(OH)2 + heatCaO + H2O Ca(OH)2 + heat

Softening reaction

regulated by controlling the pH General procedures:

FREE RADICALSARE

NEUTRALIZED

pH IS RAISED TOPRECIPITATETHE CaCO3 (s)

pH IS RAISED FURTHERTO REMOVEMg(OH)2 (s)

CO32- IS ADDED TO

PRECIPITATETHE NONCARBONATE

HARDNESSBFC 3103

ENVIRONMENTAL ENGINEERING

Continues…

6 important softening reactions (occur simultaneously in reality):

(1) NEUTRALIZATION OF CARBONIC ACID(H2CO3)

- To neutralize any free acids that may b present in the water

- NO hardness is removed in this step

(2) Precipitation of carbonate hardness due to calcium pH must raised to 10.3 to percipitate the

calcium carbonate Have to convert all of the bicarbonate to

carbonate The carbonate then serves as common ion

for percipitation reaction

HOW??

(3) Precipitation of carbonate hardness due to magnesium

Must add more lime to achieve a pH about 11.

The reaction may be considered to occur in two stages.

First stage occurs when all of the carbonate in step 2 are converted

It is SOLUBLE.sothe hardness of

water did notCHANGE

continues…

Second stage- addition of more lime to remove the hardness due to magnesium

4) REMOVAL OF NONCARBONATE HARDNESS DUE TO CALCIUM

If noncarbonate hardness need to be removed due to calcium, NO further increase in pH is required.

Instead, additional carbonate in the form of soda ash should be provided

4) REMOVAL OF NONCARBONATE HARDNESS DUE TO MAGNESIUM

To remove noncarbonate hardness due to magnesium, both lime and soda should be added

The lime provides the hydroxyl ion for percipitation of magnesium

There is NO change in the hardness

becoz the calciumis still in solution

THEN???

continues….

The calcium need to be removed by adding the soda

This is the same as rxn toRemove hardness due to

calcium

cont

Step and Chemical addition Reason

Carbonate hardness1. Lime = CO2

2. Lime=HCO3-3. Lime = Mg2+ to be removed (in excess 40 mg/L )4. Lime = required excess

Noncarbonate hardness5. Soda –nancarbonate hardness to be removed

Destroy H2CO3

Raise pH; convert HCO3- to CO3

2-

Raise pH; precipitate Mg(OH)2

Drive reaction

Provide CO32-

continues

Try this question:From the water analysis presentedbelow, determine the amount of lime and soda

(in mg/L as CaCO3) necessary to soften the

water to 80 mg/L hardness as CaCO3

-water composition (mg/L) : Ca2+ =95.20, Mg2+=13.44, Na+=25.76, CO2 = 19.36,

HCO3-=241.46, SO4

2-=53.77, Cl-=67.81

From the bar chart: TH= 293.37 mg/L as CaCO3 (noted:

CO2 –does not contribute to the hardness) CH = 198.00 mg/L as CaCO3 ; NCH = TH-CH = 95.37 mg/L.

Ca2+

HCO3-

Na+Mg2+

SO42- Cl-

0

0 mg/L as CaCO3

mg/L as CaCO3

CO2

Cont..

Step Dose (mg/L as CaCO3)

Lime = CO2

Lime=HCO3-Lime = Mg2+ - 40 = 55.37 -40Lime = excess (equal to Mg2+ to be removed)Total

44.14198.0015.37

20.00 (minimum)277.51

The amount of lime to add is 277.51 mg/L as CaCO3. the excess chosen was the minimum since (Mg2+-40) was less than 20.

Determine if any NCH need to be removed. NCHf=final hardness (80 mg/L) –the CH left (40 mg/L)

Cont..

NCHf=80-40 = 40 mg/L Thus 40 mg/L may be left. NCHR= NCHi-NCHf

= 95.37 – 40 = 55.37 mg/L Thus the amount soda to be added =

55.37 mg/L as CaCO3.

(iii) MIXING & FLOCCULATION

Mixing: is the process whereby the chemicals are quickly and uniformly dispersed in the water

During coagulation and softening, the chemical reactions that take place in rapid mixing form precipitates

AlOH / FeOH CaCO3 / MgOH

Precipitates formed in these process must be broughtinto contact with one another so that they can

agglomerate and form large particles, flocs

Contacting process:

FLOCCULATION

MIXING(i) Degree of mixing

Is measured by velocity gradient, G The higher the G value, the more violent the

mixing G is a function of the power input into a unit

volume of water

G = (P/μv)1/2velocity gradient, s-1

powerinput, W dynamic

viscosity, Pa.S

Volume of water inmixing tank, m3

continues… Mechanisme of coagulation:(i) Adsorption of the soluble hydrolysis species on

the colloid(ii) Destabilization or sweep coagulation where the

colloid is trapped in the hydroxide percipitate ~the reaction is extremely fast, occur within 1 s~G values in the range of 3,000 to 5,000 per second

and detention times on the order of 0.5 s are recommended for adsorption – desorption reaction

** for SOFTENING, detention time on the order of 5 to 10 min may be required.G values to disperse and maintain particles in suspension may be on the order of 700 per second

(ii) Rapid mix The most important physical operation

affecting coagulant dose efficiency The chemical reaction in coagulation is

completed in less than 0.1 s ~instantaneous and complete

Refer Fig 4-24, 4-25, 4-26, 4-27 in the t/book The selection of G and Gθ values for

coagulation is dependent on:

Mixing devices Chemicals selected

anticipated reaction

(iii) Rapid mix tank Mixing equipment consists of an electric

motor, gear type speed reducer and either a radial-flow impeller OR axial-flow impeller.

More turbulencePreferred to rapid mixing

continues…

Chemicals should be added below the impeller, the point of the most mixing

Tank and impeller geometries for mixing

D= impeller diameter, T = equivalent tank diameter, H = water depthB = water depth below impeller

Can be used to selectthe proper basin depthand surface area andthe impeller diameter

Fig 4-28

FLOCCULATION Rapid mix ~ most important physical factors

affecting coagulant efficiency Flocculation ~ the most important factor

affecting particle removal efficiency Objective of flocculation: brings the particles

into contact so that they will collide, stick together and grow to a size that will readily settle.

However, too muchmixing will shear the flocs particles so that the

flocs is small and finely dispersed

Enough mixing must be provided

continues… THEREFORE, the velocity gradient must be

controlled within a relatively narrow range The HEAVIER the flocs and the HIGHER the

suspended solids concentration, the MORE MIXING is required to keep the flocs in suspension

Softening flocs is HEAVIER than coagulation flocs and therefore requires a higher G value

Flocculation is normally accomplished with an axial-flow impeller (fig 4-27), a paddle flocculator (fig 4-29) or a baffled chamber (fig 4-30)

Flocculation basin should be divided into at least three compartment

(iii) Sedimentation -clarifier

The solid-liquid separation using gravity settling to remove suspended solid.

In water treatment, sedimentation used are: To settle out discrete non-flocculent particles in a

dilute suspension. To settle out flocculent particles in a dilute

suspension.

Sedimentation tank Rectangular settling tank

Influent

Scum box

Scrapper board

Sludge hopper under

Scum trough decanting channel

Effluent

Scum box

Sludge scraper

Influent

Sludge withdrawal

Scrape/scum board

Scum trough

Sloping flow

Sludge hopper

Effluent

plan

section

Circular settling tank

weir

Water in

Central inlet well

Effluent channel

Water in

Discharge

Sludge scrapper

Sludge withdrawal

Influent well

plan section

(iv) Filtration Water filtration: is a process for separating

suspended or colloidal impurities from water by passage through a poros medium, usually a bed of sand or other medium

Water fills the pores (open spaces) between the sand particles, and the impurities are left behind, either clogged in the open spaces or attached to the sand itself

Methods of classifying filters: (i) Type of medium used (sand, coal, dual media

(coal + sand), mixed media (coal +sand+garnet)(ii) Loading rate : is the flow rate of water applied per

unit area of the filter. It is the velocity of the water approaching the face of the filter

continues…

Loading rate:

Based on the loading rate, the filters are described as:

(i) slow sand filters (ii) rapid sand filters (iii) high rate sand filters

Va = Q/As

Face velocity = m/dLoading rate = m3/d.m2

Flow rate on to the filtersurface =m3/d

Area surface of filter = m2

Comparison of typical ranges for design and operating parameters for slow sand filtration and

rapid filtration

Processcharacteristics

slow sandfiltration Rapid filtration

Filtration rate 0.05 - 0.2 m/hr 5-15 m/hr

media diameter 0.3 - 0.45 mm 0.5 - 1.2mm

bed depth 0.9-1.5m 0.6-1.8m

required head 0.9 - 1.5 m 1.8 -3 m

Run length 1-6 month 1-4 days

Pretreatment none required coagulation

Regeneration method Scraping backwashing

maximum raw water turbidity 10-50 NTU

unlimited with proper pretreatment

(v) Disinfection

Is used to reduce pathogens (disease-producing microorganisms: bacteria, viruses & amebic cysts) to an acceptable level

NOT the same as STERILIZATION Purposeful disinfection must be capable of destroying all pathogens To be of practical services, such water disinfectants must posses the following

properties:

It implies the destruction of all living

microorganism.Drinking waternot to be sterile

continues…

(i) They must destroy the kinds and numbers of pathogens that may be introduced into water within a practicable period of time over an expected range in water temperature

(ii) They must meet possible fluctuations in composition, concentration and condition of the waters or wastewaters to be treated

(iii) They must be neither toxic to humans and domestic animals nor unpalatable or otherwise objectionable in required concentrations

(iv) They must be dispensable at reasonable cost and safe and easy to restore, transport, handle and apply

(v) Their strength or concentration in the treated water must be determined easily, quickly and automatically.

(vi) They must persist within disinfected water in a sufficient concentration to provide reasonable residual protection against its possible recontamination before use.

(vi) Adsorption

Is a mass transfer process wherein a substance is transferred from the liquid phase to the surface of solid where it is bound by chemical or physical forces

In water treatment, the adsorbent (solid) is activated carbon;

(i) granular (GAC)

(ii) Powdered (PAC)

continues…

GAC(i) Is added to the filter system by replacing the

anthracite (coal) with GAC – as an alternative for taste and odor control

(ii) It will last from 1 - 3 years and then must be replaced

(iii) It is very effective in removing many taste and odor compounds

(iv) It has been proposed to be used to remove naturally occuring organic matter

continues… PAC(i) Is fed to the raw water in a slurry(ii) Generally used to remove taste and odor causing

substances(iii) To provide some removal of synthetic organic

chemicals (SOCs)(iv) The advantage: the capital equipment is

inexpensive and can be used on an as-needed basis

(v) The disadvantage: the adsorption is often incomplete (sometimes even doses of 50mg/L are not sufficient)

(vii) Membranes

It is a thin layer of material that is capable of separating materials as a function of their physical and chemical properties when a driving force is applied across the membrane

In the case of water treatment, the driving force is supplied by

using a high pressure pump

The membrane type is selected

based on the constituents to

be removed

continues…

In the membrane process, the feed stream is divided into 2 streams (Fig 4-49)

(i) The concentrate OR reject stream

(ii) Permeate OR product stream

continues…

The membrane as at the heart of every membrane process and can be considered as barrier between the feed and product water that does not allow certain contaminants to pass (fig 4-50)

continues…

The efficiency @ performance of a membrane is determined by its selectivity and the applied flow.

The efficiency is called the flux and is defined as the volume flowing through the membrane per unit area and time, m3/m2.s.

The selectivity of a membrane toward a mixture is expressed by its retention, R and is given by :

R = (cp – cf)/cp x 100 %cp = [contaminant] in permeate

Cf = [contaminant] in feed

continues… Membranes can be described by a variety of

criteria including:

(i) Membrane pore size

(ii) Molecular weight cutoff (MWCO)

(iii) Membrane material and geometry

(iv) Targeted materials to be removed

(v) Type of water quality to be treated, and/or

(vi) Treated water quality

(vii) Pressure driven

(viii) Electrically driven process

IMPORTANT!!!TYPES OF FILTER MEMBRANE SYSTEM

THANK

YOU

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CHAPT 3-Water Supply (1)

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