Water requirements miscellaneous

Water requirements miscellaneous

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Water Requirements

Water requirements miscellaneous

Direction: A plain sedimentation tank with a length of 20 m, width of 10 m and a depth of 3 m is used in a water treatment plant to treat 4 million litres of water per day (4 MLD). The average temperature of water is 20°C. The dynamic viscosity of water is 1.002 × 10–3 N.s/m² at 20°C. Density of water is 998.2 kg/M³. Average specific gravity of particles is 2.65.

  1. What is the surface overflow rate in the sedimentation tank?








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    SOR =
    Q
    		 =
    4 × 106 × 10-3
    		 = 20m³/m²/days
    A20 × 10

    Correct Option: A

    SOR =
    Q
    		 =
    4 × 106 × 10-3
    		 = 20m³/m²/days
    A20 × 10

Direction: A water sample contains the following dissolved ions.
[Na+] = 56 mg/l; [Ca2+]
[Ca2+] = 40 mg/l; [Mg2+]
[Mg2+] = 30 mg/l; [Al3+]
[Al3+] = 3 mg/l; [HCO3]
[HCO3] = 190 mg/l; [Cl-]
[Cl-] = 165 mg/l; Water pH is 7.
Atomic weights: Ca: 40, Mg: 24, Al: 27, H: 1, C: 12, O: 16, Na: 23, Cl: 35.5.

  1. The non-carbonate hardness of the sample in mg/l as CaCO3 is








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    Non-carbonate hardness = Concentration of HCO-3 ×
    Eq. wt of CaCO3
    Eq. wt of HCO-3

    = 190 ×
    50
    		 = 155.7 mg/l ≈ 156 mg/l.
    61

    Correct Option: B

    Non-carbonate hardness = Concentration of HCO-3 ×
    Eq. wt of CaCO3
    Eq. wt of HCO-3

    = 190 ×
    50
    		 = 155.7 mg/l ≈ 156 mg/l.
    61

  1. The total hardness of the sample in mg/l as CaCO3 is








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    Total solids as CaCO3 (mg/l) = Concentration of Mg2+ ×
    Eq. wt of CaCO3
    		 + Concentration of Ca2+ ×
    Eq. wt of CaCO3
    Eq. wt of Mg2+Eq. wt of Mg2+

    = 30 ×
    50
    		 + 40 ×
    50
    		 = 225 mg/l of CaCO3
    1220

    Correct Option: D

    Total solids as CaCO3 (mg/l) = Concentration of Mg2+ ×
    Eq. wt of CaCO3
    		 + Concentration of Ca2+ ×
    Eq. wt of CaCO3
    Eq. wt of Mg2+Eq. wt of Mg2+

    = 30 ×
    50
    		 + 40 ×
    50
    		 = 225 mg/l of CaCO3
    1220

Direction: A city is going to install the rapid sand filter after the sedimentation tanks. Use the following data.
Design loading rate to the filter     200 m³/m²d
Design flow rate     0.5 m³/s
Surface area per filter box     50m²

  1. The number of filters required shall be








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    No. of filters =
    216
    		 = 4.32
    50

    Take 6 filters.

    Correct Option: C

    No. of filters =
    216
    		 = 4.32
    50

    Take 6 filters.

  1. The surface area required for the rapid sand after will be








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    Surface area =
    Q
    Loading rate

    =
    0.5/200
    		 = 216 m²
    24 × 60 × 60

    Correct Option: C

    Surface area =
    Q
    Loading rate

    =
    0.5/200
    		 = 216 m²
    24 × 60 × 60