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Treatment Water Quality Diseases caused by

VIEWS: 5 PAGES: 45

									Water Quality
Diseases caused by water-borne bacteria
and other microorganisms
   Diseases in man can be caused by
       Pathogenic bacteria
       Other organisms, such as viruses, protozoa, and
        worms

       Bacterial diseases         Virus diseases
         Cholera                    Infectious hepatitis

         Typhoid fever
                                   Worm diseases
         Bacillary dysentery
                                     Swimmers’ itch
Water Quality Parameters


    Physical WQP         Chemical WQP     Biological WQP
 Suspended solids    Dissolved oxygen      Pathogens
 Turbidity           Alkalinity               bacteria

 Color               Hardness                 viruses

 Taste and odor      Chlorides                protozoa

 Temperature         Fluorides                parasitic worms

                      Metals

                      Organics (BOD)     (pathogen indicators,
                      Nutrients          ex: Escherichia coli /
                      pH
                                          E-coli)
Water Quality Standards – TS266
                  Physico-chemical characteristics
TS266
         Undesirable chemicals
TS266
         Toxic chemicals
TS266
         Microbioligical characteristics
Water Purification Processes in
Natural Systems
   Impurities may be
     washed from the air
     eroded from the land surface, or
     leached from the soil
    and ultimately found their way into surface waters.

   The self-purification mechanisms of natural water
    systems include physical, chemical, and biological
    processes.
Physical Processes


   Dilution

   Sedimantation and resuspension

   Filtration

    Gas transfer
                       O2



   Heat transfer
                   F
Chemical Processes
   Chemical conversions
     that take place in stream and lakes helps to
      stabilize the pH
     that take place in water can change these
      materials into soluble form so that they will be
      usable by various aquatic organisms

       For ex. in the pipes
                                          Fe+2   Fe2O3


                                                         +2        -
                          Fe(s) + 1/2O2(g) + H2O(l)  Fe (aq) + 2OH (aq)
                     +2                                                    +
                  4Fe (aq) + O2(g) + 4H2O(l)  2Fe2O3(s, red color) + 8H (aq)


                                    Corrosion (Fe  rusting)
Biochemical Processes

   The sum of the processes by which living organisms
    assimilate and use food for subsistence, growth, and
    reproduction is called metabolism. The metabolic
    processes and the organisms involved are a vital part
    of the self-purification process of natural water
    systems.

      Microorganisms + organics  new cells + energy
          Bacteria
          Protozoa
       Other microor.s
Water Treatment




    Storage, coagulation, flocculation,
    sedimentation, filtration, chlorination
    and water softening
Water Treatment Plant - Flowchart
Storage
   Good
       number of bacteria of intestinal origin ↓
       water-borne diseases may disappear
   Due to
       sedimentation
       bactericidal action of ultraviolet radiation or
        visible light
   Bad
       growth of various forms of algae
   Due to
       increase the difficulties of treatment
    Aeration

   Goals:

       Oxygen transfer into the water  cascade and step
                                         aerators


       Removal of gaseous and volatile compounds which may
        be responsible for taste and odor  air stripping
        (for example removal of hydrogen sulfide or chlorine)
Cascade aerators used at İvedik Treatment Plant
Cascade aeration


                   Spray aeration
Screening


   To remove large floating and suspended
    debris

   Various types and sizes: bar screens, band
    and drum screens, microstrainers

   All intakes are screened. At river intakes
    plastic bottles, paper bags, branches of
    foliage, etc. may collect
    Coagulation

   Colloidal particles (1-1000 nm)
    have insufficient mass to settle
    down.                                                            large
                                                                  repulsive

    Most naturally occurring particles
                                                                    forces


    are negatively charged.
   Addition of coagulants ↓ surface
    charge and agglomerates form.
                                                                                          Al+3
                                                    Al+3
                                            Al+3                              Al+3           Al+3
                                                           Al+3 reduced
   Larges agglomerates settle down.     Al+3                     repulsive Al+3
                                                                    forces                       Al+3
   Coagulants: ferric chloride          Al+3              Al+3
                                                                                          Al+3
    [FeCl3], aluminum sulfate or alum              Al+3                            Al+3


    [Al2(SO4)3], or lime [Ca(OH)2]
   Rapid mixing
Flocculation

   Gentle mixing to speed agglomeration of colloidal material.
   Slow mixing causes small particles to collide and stick
    together.
   Particulate diameters ↑
   Doubling the particle diameter increases the settling
    velocity by a factor of 4.

                           slow mixing
       chemical
       addition




            coagulation   flocculation
                                            sedimentation
Sedimentation and settling tanks

   Designed to ↓ velocity of flow of water to permit
    suspended solids (SS) and precipitates formed in
    coagulation and flocculation to settle out by gravity

   Different type of tanks work good with different
    types of water  no hard and fast rules!

   Performance of a tank = f (amt. of SS, nature of SS,
    their shape, relative density, extent of clarification
    req’d., temp. of water, rate of flow, etc.)
Circular radial flow tank
Sedimentation tank
Rectangular basins
Sedimentation and settling tanks
 DESIGN

     Lab settling tests
     Investigate what type of tank has been successful before
      under similar conditions


 PLAIN SETTLING

     No chemicals used
     By gravity


 FALLING VELOCITY = f (horizontal flow velocity of water, the
  size of the particle, the relative density of the particle, the
  shape of the particle, and the temp. of water)
Sedimentation and settling tanks

 Theoretical velocity of falling spherical particle in
  slowly moving water, V (Camp, 1946):

                                                2
                       g        d
         V (cm / s )   r  1
                      18        

         g = 981 cm/s2
         r = the relative density of the particles = particle/fluid
         d = the diameter of the particle (mm)
          = the kinematic viscosity of water (centistokes) = f (T)
                                               1 centistoke = 1 mm2/s
Design of settling tanks

                           Flow, Q                    b
Particle X                    L                              d

                    Q/bd
                                                     Time taken = d/V
                V




                 Time taken = Lbd/Q



                            d Lbd                 Q
FOR COMPLETE REMOVAL:                     or V 
                            V   Q                 A
                        A = plan area of the basin
Design of settling tanks


                 This is the limiting speed of fall to
    Q             enable the particle to reach the bottom
 V               of the tank.
    A
                 All particles with V>Q/A will be
                  removed.

 Example: Suppose we have a tank of 300 m2 surface
   area and the rate of inflow is 1.2 m3/s. (a) What is the
   falling speed of the particles that will be completely
   removed? (b) What % of the particles with a falling
   speed of 0.2 cm/s will be removed? (Answers: 0.4 cm/s; 50%)
Water Softening
 Water hardness is caused by multivalent cations,
  usually calcium and magnesium.

 The term hard or hardness originated because waters
  containing such multivalent cations were “hard” to use
  for laundry.

 BAD
     Divalent cations in water react with soaps, reducing
      effectiveness
     Precipitates of calcium carbonate onto the walls of water
      heaters
 Water Softening

 Hardness is not a health concern  no absolute std.s

 Concentrations above 150 to 200 mg/L CaCO3 are usually
  detectable by taste.

 If hardness is below 50 mg/L CaCO3 it is difficult to remove
  the soap after the bath or shower.

 Hardness can be removed by
     Chemical treatment to ppt divalent cations
     (addition of lime [Ca(OH)2] or soda ash [Na2CO3])
     Ion exchange
Filtration
 Many particles in water are too small to be removed
  by sedimentation!

 Particles removed only when they make physical
  contact with filter medium.

 Removal occurs due to several mechanisms
   Straining  when particle is larger than the pore they are
    trapped
   Sedimentation  particles settle down on medium material

   Interception  particles are intercepted by or adhere to the
    surface of the medium due to inertia
Slow sand filtration
   Filtration Unit at
İvedik Treatment Plant
Disinfection

 Disinfection is the destruction or killing of pathogenic
  microorganisms.

 Objective of potable water disinfection
     Kill or inactivate the harmful organisms
     To leave a residual of disinfectant that will kill or inactivate
      organisms in the distribution system.

 Disinfectants
     gaseous chloride, chloride dioxide, calcium hypochlorite, sodium
      hypochlorite, etc.
     Ozone
     UV
Disinfection

 An ideal disinfectant                              Chlorine   Ozone   UV
     Must kill microorganisms                          √         √     √X
     Should leave a residual for the distribution      √         X     X
      system
     Should be inexpensive                             √         X     √
     Should not be harmful to humans or create         X         X     √
      harmful byproducts
     Should be safe to handle and use                  X        √X     √
     Should not harm the environment or create         X        √X     √
      an undesirable taste or odor
Chick’s Law

    Harriet Chick in 1900s  a method of estimating the
     destruction of microorganisms by disinfectants as a function
     of time.

    dN                N0 = initial concentration of microorganisms (no./mL)
          kN
     dt               N = concentration of microorganisms at time t (no./mL)
        N           t = time of disinfection (hr)
    ln       kt   k = an empirical constant descriptive of the particular
        N0               microorganisms and disinfectant in use (hr-1)
İvedik Treatment Plant

   13 km north of Ankara
   4 units each having a capacity of 564,000 m3/day
   water quality at the exit of the treatment plant
    are in accordance with WHO and TS266
    standards
   combined treatment for
    water from Çamlıdere
    and Kurtboğazı Dams
İvedik Treatment Plant
Example – İvedik Treatment Plant

                                         Polyelectrolyte
                                   Aluminum sulfate        Chlorine
                                                                        Slow mixing
Kurtboğazı
   dam       Aeration         Blending           Prechlorination        Flocculation
Çamlıdere dam                 chamber                 and                   and
                                                  Coagulation          Sedimentation
                                                  Rapid mixing
                                                                           Sludge

                        Chlorine


      Filtration        Chlorination          Equalization tank        ANKARA


                                                In plant utilization
Water quality criteria of clean water exiting
İvedik Treatment Plant
 Quality Parameters   Clean Water     World Health       Spring water
                      From Ivedik   Organization Std.s   (memba suyu)
                          T.P.
Color (Pt-Co)              5                5                 3

Taste                  Tasteless        Tasteless         Tasteless

Odor                   Odorless         Odorless           Odorless

pH                      6.3-7.6           7-8.5              7.5

Turbidity (NTU)         0.3-1.0            5.0               0.5

Iron, Fe (mg/L)           0.1              0.1              None

Manganese, Mn            0.05             0.05              None
(mg/L)
Hardness (FSº)          8.3-12.5           10.0              2.5

Coliform                 None             None              None
Questions?

								
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