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:!!:WATER & WASTEWATER ENGINEERING AT A GLANCE :!!:, SLOW SAND FILTER…

- - - - Protozoa
      - Bacteria
      - Viruses
      - Helminth
- - - - Occurs if the particles are too large to fit between the fiber spaces
      - :red_cross: Not so favourable as the particles passes through the settling tank us very fine
    - - Breakdown of particles in the water
      - Occurs when formation of a film 'Schmutzdecke' (at upper grains of sand layer)
    - - Occurs when the particles become attracted and sticking to the media
        
        INERTIAL IMPACTION
        
        DIFFUSION
        
        INTERCEPTION
- - - - To remove objectional metal in water
  - - - Corrosive to piping :!:
        
        Produce rotten egg odor :red_cross:
  - - - Cascade aerator
      - Cone aerator
      - Spray aerator
    - - Diffuse aerator
  - - - Add in coagulant
        
        Primary coagulant
        
        Destabilize the particles
        
        Coagulant aid
        
        To add density and toughness to prevent break up
        
        Expensive
      - Rapid / Flash Mixing
        
        To disperse & distribute the chemical evenly through the water
        
        Very fast (100 rpm) in 1 minute
        
        MECHANICAL MIXER
        
        HYDRAULIC MIXER
    - - Slow Mixing
        
        Enhancing particle collision & promote floc formation
        
        Very slow (30 rpm) in 25 to 30 minutes
        
        MECHANICAL FLOCCULATOR
        
        HYDRAULIC FLOCCULATOR
    - - Double Layer Compression
      - Charge Neutralization
      - Inter - Particle Bridging
      - Sweep Coagulation
    - - Surface Area: Volume Ratio
        
        Large colloid: S < V moves vertically
        
        Small colloid: S > V moves horizontally (Brownian Motion)
      - Particle Charges
        
        Repulsive force (Stable) :red_cross:
        
        Attraction force / Floc (Destabilize) :check:
    - - pH
      - Temperature :fire:
      - Time
      - Mixing & Turbulence
      - Coagulant Types
      - Coagulant Dosage
      - Characteristics of Water
    - - Type I
        
        High Turbidity & High Alkalinity
      - Type II
        
        High Turbidity & Low Alkalinity
      - Type III
        
        Low Turbidity & High Alkalinity
      - Type IV
        
        Low Turbidity & Low Alkalinity
    - - A process of removing solid particles heavier than water by gravity settling
        
        Discrete particles
        
        Particles whose size, shape and specific gravity do not change with time
        
        Flocculent particles
        
        Particles whose changing size, shape and specific gravity upon contact with other particles
        
        Dilute suspension
        
        Concentration of suspension is not sufficient to cause significant displacement of water as they settle
        
        Concentrated suspension
        
        Concentration is high and cause displacement of water as they settle
      - Type of settling behaviors
        
        Type I
        
        Discrete Particles + Dilute Suspension
        
        Settle individually
        
        Type II
        
        Flocculent Particles + Dilute Suspension
        
        Agglomerate & increase settling velocity
        
        Type III
        
        Flocculent Particles + Concentrated Suspension
        
        High concentration & Settle as a floc close to the bottom of the settling tank
        
        Type IV
        
        Flocculent Particles + Concentrated Suspension
        
        Compression settling & Reduce the spaces of void
      - Equations & Parameters
        
        Settling Velocity
        
        Reynolds number
        
        Laminar Flow
        
        Transition Flow
        
        Turbulent Flow
        
        Drag Coefficient
      - Type of settling tank
        
        Methods of Operation
        
        Fill & draw type tank
        
        Takes a very long time & not economical
        
        Continuous flow type tank
        
        Increase the length of tank to decrease the velocity
        
        Location
        
        Preliminary
        
        Before coagulation & flocculation process
        
        Primary
        
        After coagulation & flocculation process
        
        Secondary
        
        For wastewater treatment process
        
        Shape
        
        Circular tank
        
        Long Rectangular tank
        
        Hopper Bottom tank
      - 4 Zones in Settling Tank
        
        INLET ZONE
        
        Provide a smooth transition from influent flow to the tank and to prevent short circuiting in the tank
        
        To prevent breakup of floc
        
        SETTLING ZONE
        
        Provide calm area for the suspended particles to settle
        
        Water velocity greatly reduced in this zone
        
        OUTLET ZONE
        
        Provide a smooth transition from sedimentation tank to the outlet
        
        SLUDGE ZONE
        
        Provide storage area for sludge before it is removed for additional treatment or disposal
      - Plate & Tube Settler
        
        Purpose
        
        Increase settling capacity by reducing the vertical distance of a floc
        
        Inclination
        
        :check: 45 to 60 deg: SELF CLEANING EFFECT
        
        :red_cross: > 60 deg: EFFCIENCY DECREASED
        
        :red_cross: 45 deg: SETTLER WILL TEND TO ACCUMULATE SOLIDS
- - - - 4. Tank Dimension
        
        5. Sludge Zone Depth
        
        6. Efficiency