Treatment of Sewage Notes | EduRev

Environmental Engineering

Civil Engineering (CE) : Treatment of Sewage Notes | EduRev

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Sedimentation Tank

Settling Velocity


  1. Treatment of Sewage Notes | EduRev
    for d < 0.1 mm
    Where,
    Vs = The velocity of the settlement of particle or settling velocity in m/sec.
    d = The diameter of the particle in the meter.
    G = Specific gravity of the particle.
    v = Kinematic viscosity of water in m2/sec.
    Treatment of Sewage Notes | EduRev Y = Dynamic viscosity
    δ = Density

  2. Treatment of Sewage Notes | EduRev
    where,
    Treatment of Sewage Notes | EduRev
    → For laminar flow
    Re = Reynolds number
    Treatment of Sewage Notes | EduRev
    Treatment of Sewage Notes | EduRev for transition flow.
    Treatment of Sewage Notes | EduRev for turbulent flow.

  3. Treatment of Sewage Notes | EduRev
  4. Newtons Equation for Turbulent Settling
    Treatment of Sewage Notes | EduRev
  5. Modified Hazen’s Equation for Transition Zone
    (i)
    Treatment of Sewage Notes | EduRev
    Where T = Temperature in oC.
    (ii) Putting G = 2.65 for Inorganic Solids
    Treatment of Sewage Notes | EduRev
    (iii) Putting G = 1.2 for Organic Solids
    Treatment of Sewage Notes | EduRev

Critical Scour Velocity in Constant Velocity Horizontal Flow

Grit Chamber (VH)
Treatment of Sewage Notes | EduRev

Proportional Flow Weir
Treatment of Sewage Notes | EduRev

Treatment of Sewage Notes | EduRev
Where,
B = Width of the channel.
Vh = Horizontal flow velocity.
Cd = Coefficient of discharge.
x and y are coordinates on weir profile.

Parabolically or V-Shaped Grit Chamber Provided with a Parshall Flume

  1. Parshall Flume
    Treatment of Sewage Notes | EduRev
    Where,
    W = Width of the throat in the meter.
    Flow in (m3/sec) through Parshall flume.
    Ha = Depth of flow in the upstream leg of a flume of one-third portion in the meter.
    Treatment of Sewage Notes | EduRev
  2. Parabolic Grit Channel
    Treatment of Sewage Notes | EduRev
    Where,
    n = Discharge coefficients of the control section.
    = 1.5 for partial flume.
    = 1 for proportional flow weir.
    (i) Aerated Grit Channels
    Treatment of Sewage Notes | EduRev
    (ii) Detritus Tank
    Treatment of Sewage Notes | EduRev

Skimming Tank

  1. Detention Period = 3 to 5 minutes.
  2. Amount of compressed air required = 300 to 6000 m3 per million liters of sewage.
  3. Surface Area,
    Treatment of Sewage Notes | EduRev
    Where,
    q = Rate of flow of sewage in m3/day.
    Vr = Min. rising velocity of greasy material to be removed in m/min
    = 0.25 m/min mostly.

Vacuators

Vacuum Pressure = 0 to 25 cm of Hg
For 10 to 15 minutes.

  1. Sedimentation Tank
    (i) Overflow rate
    = 40000 to 50000 lit/m2 day for plain sedimentation.
    = 50000 to 60000 lit/m2 day for sedimentation with coagulation.
    = 25000 to 35000 lit/m2 day for secondary sedimentation tank
    (ii) Depth ~ 2.4 to 3.6 m.
    (iii) Detention time = 1 to 2 hour.
    (iv) width = 6.0 m
    (v) Length = 4 to 5 times width.
    (vi) Velocity of flow Vf = 0.3 m/min.
    (vii)
    Treatment of Sewage Notes | EduRevWhere,V = Flow velocity
    B = Width of the Basin
    H = Depth of sewage in the tank.
    (viii)
    Treatment of Sewage Notes | EduRev
    (ix)
    Treatment of Sewage Notes | EduRev
    Treatment of Sewage Notes | EduRev
  2. Detention Time
    (i)
    Treatment of Sewage Notes | EduRev
    For rectangular Tank
    (ii)
    Treatment of Sewage Notes | EduRev
    for circular tank
    Where
    d = Dia of the tank
    H = Vertical depth of wall or side depth
  3.  Displacement Efficiency (η)
    Treatment of Sewage Notes | EduRev

Trickling Filter

  1. Conventional Trickling Filter or Low Rate Trickling Filter
    Treatment of Sewage Notes | EduRev
    Where,
    η = The efficiency of the filter and its secondary clarifier, in terms of % of applied BOD
    u = Organic loading in kg/ha-m/day applied to the filter (called unit organic loading)
  2. High Rate Trickling Filter
    (i)
    Treatment of Sewage Notes | EduRev
    Where, F = Recirculation factor
    Recirculation ratio
    (ii)
    Treatment of Sewage Notes | EduRev
    Where,
    Y = Total organic loading in kg/day applied to the filter i.e. the total BOD in kg.
    Y/VF = Unit organic loading in kg/Ha-m/day
    V = Filter volume in Ha-m.
    % efficiency of single-stage high rate trickling filter.
    (iii)
    Treatment of Sewage Notes | EduRev
    Where,
    n' = Final efficiency in the two-stage filter.
    Y' = Total BOD in the effluent from the first stage in kg/day.
    F' = Recirculation factor for second stage filter
    V' = Volume in second stage filter in ha-m.
    Treatment of Sewage Notes | EduRev
    Treatment of Sewage Notes | EduRev
    Dunbar Filter
    Surface loading = 25000 MI/m2/day.
    BOD removed = 85%
    Sludge and its Moisture Content
    Treatment of Sewage Notes | EduRev
    The volume of sludge at moisture content P1%
    The volume of sludge at moisture content P%

Sludge Digestion Tank

  1. When the change during digestion is linear.
    (i)
    Treatment of Sewage Notes | EduRev
    Where,
    The volume of digestion in m3.
    Raw sludge added per day (m./day)
    Equivalent digested sludge produced per day on completion of digestion, m3/day.
    Digestion period in the day.
    (ii)
    Treatment of Sewage Notes | EduRev
    with monsoon storage
    Where,
    T = Number of days for which digested sludge (V2) is stored (monsoon) storage)
  2. When the change during digestion is parabolic.
    (i)
    Treatment of Sewage Notes | EduRev
    without monsoon storage
    (ii)
    Treatment of Sewage Notes | EduRev
    without monsoon storage
    Treatment of Sewage Notes | EduRev

Destruction and Removal Efficiency (DRE)

Treatment of Sewage Notes | EduRev
Where,
Win = The mass fill rate of one POHC (Principal organic Hazardous constituent) in the waste stream.
Wout = Mass emission rate of the same POHC present in the exhaust emission prior to release to the atmosphere.

Aeration Tank (ASP)
Treatment of Sewage Notes | EduRev

  1. Detention period,
    Treatment of Sewage Notes | EduRev
    Where
    V = Volume of the tank in m3.
    Q = Quantity of wastewater flow into the aeration tank excluding the quantity of recycled sludge (m3/day)
  2. Volumetric BOD Loading or Organic Loading, (U)
    Treatment of Sewage Notes | EduRev
    Where,
    QYo = Mass of BOD applied per day to the aeration tank through influent sewage in gm.
    V = The volume of the aeration tank in m3.
    Q = Sewage flows into the aeration tank in m3.
    BOD5 in mg/lit (or gm/m3) of the influent sewage.

  3. Treatment of Sewage Notes | EduRev
    Where,
    F/M = Food (F) to Microorganism (M) ratio QYo = Daily BOD applied to the aeration system in gm.
    Yo = 5 day BOD of the influent sewage in mg/lit.
    Q = The flow of influent sewage in m3/day.
    MLSS (Mixed liquor suspended solids) in mg/lit.
    V = The volume of the Aeration Tank (lit).
    M = XtV = Total microbial mass in the system in gm.
  4. Sludge Age (θc)
    Treatment of Sewage Notes | EduRev
    Where,
    XT = The concentration of solids in the influent of the Aeration Tank called the MLSS i.e. mixed liquor suspended solids in mg/lit.
    V = Volume of Aerator
    Qw = The volume of waste sludge per day
    The concentration of solids in the returned sludge or in the wasted sludge (both being equal) in mg/lit.
    Q = Sewage inflow per day.
    XE = The concentration of solids in the effluent in mg/lit.
  5. Sludge Volume Index (S.V.I)
    Treatment of Sewage Notes | EduRev
    Where,
    Xab = Concentration of suspended solids in the mixed liquor in mg/lit.
    Vab = Settled sludge volume in ml/lit.
    S.V.I = Sludge volume index in ml/gm.
  6. Sludge Recycle and Rate of Return Sludge
    QR·XR = (Q + QR) x R
    Treatment of Sewage Notes | EduRev
    Where,
    QR = Sludge recirculation rate in m3/day.
    Xt = MLSS in the aeration tank in mg/lit.
    XR = MLSS in the returned or wasted sludge in mg/lit.
    Treatment of Sewage Notes | EduRev
    S.V.I = Sludge volume index in ml/gm.
    (i) Specific substrate utilization rate
    Treatment of Sewage Notes | EduRev
    αy = 1 for MLSS and 0.6 for MLVSS,  ke = 0.66
    (ii) Oxygen Requirement of the Aeration Tank
    Treatment of Sewage Notes | EduRev
    Where,
    Treatment of Sewage Notes | EduRev
    (iii) Oxygen Transfer Capacity (N)
    Treatment of Sewage Notes | EduRev
    Where,
    N = Oxygen transferred under field conditions in kg O2/k.wh (Or MJ)
    Ns = Oxygen transfer capacity under standard conditions in kg O2/kwh (or MJ)
    Ds = Dissolved oxygen-saturation value for sewage at operating temperature.
    DL = Operation D.O level in Areation tank usually 1 to 2 mg/lit.
    T = Temperature in oC
    α = Correction factor for oxygen transfer for sewage usually 0.8 to 0.85.

Oxidation Ponds

  • Depth → 1.0 to 1.8 m.
  • Detention period → 2 to 6 weeks.
  • Organic loading → 150 to 300 kg/ha/day.
  • Under hot condition → 60 to 90 kg/ha/day.
    Under cold conditions.
  • Length to width ratio = 2
  • Sludge Accumulation = 2 to 5 cm/year
  • Minimum depth to be kept = 0.3 m.

For Inlet Pipe Design

Assume V = 0.9 m/s
Assume flow for 8 hrs.

For Outlet Pipe Design

Dia of outlet = 1.5 dia of the inlet pipe

Septic Tank

  • Detention time = 12 to 36 hr.
  • Sludge accumulation rate = 30 lit/cap/year.
  • Sewage flow = 90 to 150 lit/capita/day.
  • Cleaning period = 6 to 12 months
  • Length to width ratio = 2 to 3 m.
  • Depth = 1.2 to 1.8 m
  • Treatment of Sewage Notes | EduRev
  • Free board = 0.3 m.
    Volume of Septic Tank = (Sewage flow x Detention time) + (Sludge accumulation rate) x Clearning rate
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