Water treatment part 3 groundwater treatment
This presentation is the property of its rightful owner.
Sponsored Links
1 / 40

Water Treatment Part 3 Groundwater Treatment PowerPoint PPT Presentation


  • 111 Views
  • Uploaded on
  • Presentation posted in: General

Water Treatment Part 3 Groundwater Treatment . Dr. Abdel Fattah Hasan. Groundwater (GW) are usually:. Cool and uncontaminated Has uniform quality Usually used directly for municipal use (just chlorine is added to avoid post contamination) Sometimes GW is polluted or contaminated with:

Download Presentation

Water Treatment Part 3 Groundwater Treatment

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Water treatment part 3 groundwater treatment

Water TreatmentPart 3Groundwater Treatment

Dr. Abdel Fattah Hasan


Groundwater gw are usually

Groundwater (GW) are usually:

  • Cool and uncontaminated

  • Has uniform quality

  • Usually used directly for municipal use (just chlorine is added to avoid post contamination)

    Sometimes GW is polluted or contaminated with:

  • Hardness

  • Fertilizers

  • WW

  • Pesticides

  • Radionuclides

  • Toxic metals, such as Arsenic


Gw treatment options

GW Treatment Options


Hardness removal precipitation softening

Hardness Removal - Precipitation softening

  • Hardness of water is caused by divalent cations, such as Ca & Mg ions

  • Max. hardness for public supply: 300 -500 mg/l as CaCO3

  • Moderate hardness for public supply: 60 -120 mg/l as CaCO3

  • Precipitation softening uses lime CaO and soda ash Na2CO3 to remove Ca and Mg

  • Lime slurries are usually has the form Ca(OH)2

  • Lime treatment has the incidental benefits of bacterial actions, removal of iron and aid in clarification of turbid surface water

  • Carbon dioxide can be applied after lime treatment to lower pH by converting the excess hydroxide ion and carbonate ion to bicarbonate ion


Converting ca and mg into mg l caco 3

Converting Ca and Mg into mg/l CaCO3

  • Ca Hardness as mg/l CaCO3 = Ca (meq/l) X 50

  • Mg Hardness as mg/l CaCO3 = Mg (meq/l) X 50


Chemical reactions in precipitation softening

Chemical reactions in precipitation softening

1- Lime added to water reacts first with any available CO2

  • CO2 + Ca(OH)2 = CaCO3 + H2O

  • Ca(HCO3)2 + Ca(OH)2 = 2 CaCO3 + 2H2O

    Mg(HCO3)2 + Ca(OH)2 = CaCO3 + MgCO3+ 2H2O

    MgCO3 + Ca(OH)2 = CaCO3 + Mg(OH)2

  • Mg(HCO3)2 + 2Ca(OH)2 = 2 CaCO3 + Mg(OH)2 + 2H2O

  • MgSO4 + Ca(OH)2 = CaSO4 + Mg(OH)2

  • CaSO4 + Na2CO3 = CaCO3+Na2SO4

1 eq to one eq

2- Then Lime reacts with any calcium bicarbonate present in water

3- Then Lime reacts with magnesium bicarbonate

2eq of lime to one eq Mg(HCO3)2

4- Non-carbonate Ca (sulfate or chloride) require addition of soda ash and non-carbonate Mg (sulfate or chloride) require both lime and soda ash

1 eq to one eq

1 eq to one eq

Note: Ca ion can be effectively removed by lime addition (pH = 10.3), but Mg ion demand higher pH, so lime should be added in excess of about (35 mg/l; 1.25 meq/l)


Re carbonation

Re-carbonation

  • Used to stabilize excess lime of treated water by adding CO2:

    • Ca(OH)2 +CO2 = CaCO3 + H2O

    • CaCO3 +CO2 +H2O = Ca(HCO3)2


Excess lime softening

Excess lime softening

  • Calcium can effectively reduced by lime addition, but magnesium removal need excess lime

  • Lime and Soda ash dosages to be estimated by chemical equations PLUS excess lime for Mg removal

  • Practical limits (remains after estimation of theoretical dosages from chemical equations) for hardness removal are:

    - CaCO3: 30 mg/l as CaCO3 (= 0.6 meq/l Ca++)

  • Mg(OH)2 :10 mg/l as CaCO3 (= 0.2 meq/l Mg++)

    Note: Sodium (Na) concentration is usually increased by the amount added in the Soda ash


Excess lime softening1

Excess Lime Softening


Selective calcium carbonate removal

Selective Calcium Carbonate Removal

  • Used to soften water with low Mg hardness (less than 40 mg/l as CaCO3)

  • Enough lime is added to remove Ca without Excess.

  • Soda ash mayor may not be required, depending on the contents of non-carbonate hardness.

  • Recarbonation is usually performed to reduce scale formation.


Selective calcium carbonate process

Selective Calcium Carbonate Process


Split treatment softening

Split-Treatment Softening

By dividing the raw water into two portions for softening in a two stage system

QP MgR

QR

MgR

QE

MgE

  • Split treatment can result in chemical savings

  • Recarbonation my not be required

  • Split around 1st stage is determined by the level of Mg desired in treated water

  • Mg in treated water = (QP X MgR + QE X 10)/QR


Water treatment part 3 groundwater treatment

  • Example:

    Water defined by the following analysis is to be softened by excess lime treatment. Assume that the practical limit of hardness removal for CaCO3 is 30 mg/l and of Mg(OH)2 is 10 mg/l as CaCO3

    CO2= 8.8 mg/l

    Ca++ = 40mg/l

    Mg++ =14.7mg/l

    Na+ = 13.7mg/l

    Alk (HCO3-) =135 mg/l as CaCO3

    SO4= 29mg/l

    Cl- = 17.8mg/l

    (a) Sketch a meg/l bar graph and list the hypothetical combination of chemical compounds in solution

    (b) Calculate the softening chemicals required, expressing lime dosage as CaO and soda ash as Na2CO

    (d)Draw a bar graph for softened water before and after recarbonation. Assume that half the alkalinity in the softened water is in the bicarbonate form.


Water treatment part 3 groundwater treatment

Calcium hardness = 2X 50 = 100 mg/l as CaCO3

Magnesium hardness = 1.2X 50= 60.5 mg/l as CaCO3

Required lime dosage = 4.31 X28 +35 = 156

Dosage of Soda ash = 0.51* 53= 27 mg/l Na2CO3


Water treatment part 3 groundwater treatment

3.21

0.0

2.00

3.81

(A)

0.0

2.70

3.30

3.81

0.0

0.6

0.8

1.91

Ca++

OH-

(B)

1.25 of excess lime

0.0

0.2

0.8

1.40

1.91

0.0

0.6

0.8

1.91

(C)

0.0

0.4

0.8

1.40

1.91


Iron and manganese removal

Iron and manganese removal

  • Fe++ and Mn++ soluble in groundwater exposed to air these reduced to insoluble Fe+++ and Mn++++

  • Rate of oxidation depend on pH, alkalinity, organic content and present of oxidizing agents

  • Filtration – sedimentation and filtration

    • Fe++ ( ferrous) + oxygen Fe Ox ( ferric oxidizes)

    • Manganese can not oxidized as easily as iron need to increase pH

  • ِaeration –chemical oxidation – sedimentation- filtration

    • Fe++ + Mn++ + oxygen FeOx + MnO2 ( ferric oxidizes)

Free chlorine residual


Iron and manganese removal1

Iron and manganese removal

  • Fe (HCO3)2 + KMn O4 Fe (OH) 3 + Mn O2

  • Mn(HCO3)2 + KMnO4 MnO2

Potassium permanganate

Potassium permanganate


Iron and manganese removal2

Iron and manganese removal

  • Manganese zeolite process

  • Figure 7-20


Water treatment part 3 groundwater treatment

Figure 7-20

Aeration optional

Well water

Anthracite medium

Dry KMnO4

................................................................................................................................................

Manganese treated greensand

Dissolving tank and solution feeder

Under drain

Pressure filter

Finished water


Water stabilization

Water Stabilization

  • Ferrous metal when placed in contact with water results in an electric current caused by the reaction between the metal surfaces and existing chemicals in water

    • Fe Fe++ + 2electron

    • 2 elec + H2O + ½ O2 OH-

    • 2Fe++ + 5H2O + ½ O2 Fe(OH)3 + 4 H+

  • To Protect ductile iron pipe against internal corrosion is by lining with thin layer of cement mortar placed during manufacturing


  • Ion exchange softening and nitrate removal

    Ion- exchange softening and nitrate removal

    • Ions of a particular species in solution are replaced by ions of a different species attached to an insoluble resin


    Ion exchanger

    Ion Exchanger


    Water treatment part 3 groundwater treatment

    Cation exchange softening

    Ca ++

    Mg ++

    CaR

    MgR

    + Na+

    In Process of Removal

    +Na2R

    CaR

    MgR

    Ca ++

    Mg ++

    excess

    Regeneration

    + NaCl

    Na2R +

    NaCl


    Water treatment part 3 groundwater treatment

    Anion exchange for Nitrate Removal

    Nitrate removal

    So =4

    NO-3

    RSO4

    RNO3

    RCl +

    + Cl -

    Regeneration

    with NaCl

    Disadvantages : high operating costs and problem

    of brine disposal


    Removal of dissolved salts

    Removal of dissolved salts

    • Distillation : (desalination of sea water)

      • heating sea water (35000 mg/l mostly NaCl) to boiling point and converting it into steam to form water vapor that is condensed yielding salt free water


    Removal of dissolved salts1

    Removal of dissolved salts

    • Reserves osmosis

      • Forced passage of the natural osmotic pressure to accomplish separation of water and ions


    Water treatment part 3 groundwater treatment

    Semi permeable

    Membrane

    P> P0

    Po

    ..........................................................................................................................................................................................................................................................................

    ................................................................................................................................................................................................................................

    ......................................................................................................................................................................................

    Saline

    water

    Fresh

    water

    Osmosis

    Reverse

    osmosis

    Osmosis

    equilibrium

    (b)

    (c)

    (a)


    Reverse osmosis system

    Reverse osmosis system

    • Pretreatment unit

    • Pump to provide high pressure

    • Post-treatment

    • Brine disposal


    Water treatment part 3 groundwater treatment

    Reverse osmosis models

    Alkali

    Saline water

    Permeate (product water)

    Scale inhibitor

    Waste brine

    Pump

    Granular-media filter

    Acid

    10-30% of saline feed

    Cartridge filter


    Source of wastes in water treatment

    Source of wastes in water treatment

    • Residue from chemical coagulation

    • Precipitation from softening

    • Filter back wash

    • Settled solid from pre-sedimentation

      Total Sludge Solids produced in WT (lb/mil gal) =

      8.34 x [0.44 x alum dosage (mg/l)+ 0.74 x Turbidity (NTU)]


    Example 7 16

    Example 7-16

    • A surface water treatment plant coagulant a raw water having a turbidity of 9 units by applying an alum dosage of 30 mg/l.

      • Estimate the total sludge solids production in pounds per million gallons of water processed.

      • Compute the volume of sludge from the settling basin and filter backwash water using 1% solid concentration in the sludge and 500 mg/l of solids in the waste water. Assume 30% of total solids are removed in the filter.


    Water treatment part 3 groundwater treatment

    Applying Eq. 7-39

    Total sludge solids =

    8.34 (0.44 X 30 + 0.74 X 9)= 166 lb/ mil gal

    Solids in sludge = 0.70 X 166 = 116 lb/ mil gal

    Solids in backwash water = 0.30 X 166

    = 50 lb/ mil gal

    Volume =

    Sludge solids (lb)

    Solids fraction X 8.34 (lb/ gal)

    116

    Sludge volume =

    = 1390 gal/mil gal

    1.0

    100

    X 8.34

    Wash- water volume = 50

    500

    1,000,000

    X 8.34

    = 12,000 gal/mil gal


    Water treatment part 3 groundwater treatment

    PRECIPITATE PRODUCED

    COMPONENT IN WATER


    Dewatering and waste disposal of wastes from water treatment plants

    Dewatering and waste disposal of wastes from water treatment plants

    • Lagoons

    • Drying beds

    • Gravity thickening

    • Centrifugation

    • Pressure filter


    Water treatment part 3 groundwater treatment

    Gravity thickening

    Sludge in flow

    Inlet baffle

    Supernatant

    overflow

    Weir

    Pickets

    Scraper blades

    Sludge discharge


    Water treatment part 3 groundwater treatment

    Filtration pressure


    Water treatment part 3 groundwater treatment

    Centrifugation


    Example

    Example

    • Case 1: Groundwater source with small infrequent possible contamination used for domestic use

    • Solution : chlorination or ozonation or filtration


    Example 2

    Example 2

    • Surface water: floating matter, high suspended matter, high turbidity, considerable, biological contamination, clay

    • Solution: screening, sedimentation, coagulation, flocculation, filtration, chlorination


  • Login