Top Banner

of 14

ce152_BSP

Apr 14, 2018

Download

Documents

smishra2222
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript

  • 7/29/2019 ce152_BSP

    1/14

    1

    Ocean Disposal of Wastewater

    (An Introduction)

    by

    Prof. B. S. PANI

    I. I. T. Bombay, Mumbai

  • 7/29/2019 ce152_BSP

    2/14

    2

    Ocean is utilized as the ultimate sink for wastewater

    disposal.

    The effluent (a very dilute mixture of human & otherwastes) is collected and led to a central location.

    After treatment, the effluent is discharged into the ocean.

  • 7/29/2019 ce152_BSP

    3/14

    3

    Density of effluent is close to that of fresh water.

    Due to buoyancy effects, the effluent rises to the surface and

    in doing so entrains the ambient fluid and becomes very dilute.

    Dilution is the solution to pollution.

  • 7/29/2019 ce152_BSP

    4/14

    4

    In deep stratified oceans the diluted pollutants field may

    attain an equilibrium level below the ocean surface.

    In shallow seas the pollutants reach the sea surface and

    spreads out due to density differences that persists.

    Due to wastewater treatment dilution and inactivation of

    pathogens the quality of water becomes acceptable.

  • 7/29/2019 ce152_BSP

    5/14

    5

    Royal Commission on environmental pollution (1984) states that:

    .. with well designed sewage outfalls we believe that discharge of

    sewage to the sea is not only acceptable but in may cases environmentally

    preferable to alternative method ofdisposal.

    There is cultural feeling among some indigenous people that no

    water should be polluted with human waste.

  • 7/29/2019 ce152_BSP

    6/14

    6

    Scarcity of land for constructing a sewage treatment plant

    favors treatment of the effluent in the action.

    When sewage is diluted one hundred times, it is as good asa fully treated secondary effluent.

    Certainly there are good reasons for not disposing wastes

    containing toxic materials and heavy metals in the ocean.

  • 7/29/2019 ce152_BSP

    7/14

    7

    Secondary treatment plant: The action of bacteria and other

    micro-organisms in an enclosed basin help to reduce the sewage

    waste.

    Primary treatment: physical operations like screening and

    sedimentation are used to remove floating and settable solids.

  • 7/29/2019 ce152_BSP

    8/14

    8

    Purification in the ocean can be to some extent controlled bysite choice, design of the diffuser, and the rate of loading. All

    other processes occur naturally following discharge of effluent.

    In contrast, the purification in a treatment plant is closely

    controlled.

    Concentration of a pollutant =mixtureofVolume

    pollutantofMass,ppm etc.

  • 7/29/2019 ce152_BSP

    9/14

    9

    The local environmental impact is increased by the concentration

    Dilution =aC(C

    )a

    Co

    (C

    Where, Co & Ca = effluents and ambient concentration respectively.

    Initial dilution S= Minimum dilution achieved where the mixed

    effluent reaches the water surface or trapping level, at a distance of

    the orders of the water depth downstream. Initial dilution is water the

    control of the engineer.

  • 7/29/2019 ce152_BSP

    10/14

    10

    In still water S=f(Fr, H/D,o) and is independent of Reynoldsnumber (inertia/ viscous force) exceeding 2000.

    Densimetric Froude number =

    gd

    u

    ao

    o

    For jets Fr

    For plumes Fr 1

    For most outfalls the Fr lies between 4 to 18 and the flow can be

    classified as Buoyant jets.

    = Inertia/ buoyancy

    force per unit mass

  • 7/29/2019 ce152_BSP

    11/14

    11

    The velocity and concentration distributions are nearly Gaussian

    The initial volume and specific momentum fluxes for a circular

    jet are

    o2 uD

    4

    oQ

    2o

    2o UD

    4

    M

    Average dilution for a round jet

    1o

    21

    o QM0.29oQQS x

    Average dilution for a round plume

    1oQzoF0.163S

    35

    31

    (Specific momentum)

    Where the initial buoyancy flux ga

    ud4

    oF o2

  • 7/29/2019 ce152_BSP

    12/14

    12

    Example: Estimate the average dilution for uo=1.2m/s, D=0.15m, H=15m

    When the outfall discharges into

    a) a fresh water lake

    b) the ocean with relative density difference of 0.02

    Solution:/s3m210x2.121.2x20.15x

    4oQ

    2/s4m210x2.5421.2x20.15x4

    oM

    In fresh water

    32.712)10x(2.12x15x2

    1)210x(2.54x0.29S

    In the ocean:310x4.169.81x0.02x1.2x20.15x

    4

    oF

    1131)210x(2.1235

    1531)310x(4.160.163S

    u

  • 7/29/2019 ce152_BSP

    13/14

    13

    In the presence of buoyancy, dilution is

    enhanced.

    Cross flow of ambient helps to dilute the

    effluent in a significance way.

    Eq. Shape & Moore(1987)

    Say,

    Thus, a four fold increase in dilution takes place

    1.33o

    0.359

    o

    aoM S)u

    u1.57(SS

    1.0,100 o

    a

    o

    u

    uS

    0.1uu100,S

    o

    ao

    414100x1.59(0.1)100S 1.330.359M

  • 7/29/2019 ce152_BSP

    14/14

    14

    THANK YOU