Water Filtration: Mechanisms and Processes
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Questions and Answers

What is the primary purpose of filtration in the context of water treatment?

  • To remove suspended particles and bacteria (correct)
  • To add minerals to the water
  • To increase the water's temperature
  • To enhance the taste of the water

    • Which filtration mechanism involves particles moving randomly within the fluid due to thermal gradients?

  • Inertia attachment
  • Sedimentation
  • Brownian diffusion (correct)
  • Interception

    • What is the term used to express the size of sand filter media?

  • Texture size
  • Grain size
  • Effective size (correct)
  • Density size

    • Which filtration mechanism is primarily responsible for capturing large particles that closely follow the streamlines?

    <p>Interception</p> Signup and view all the answers

    When does inertia attachment occur in the context of filtration mechanisms?

    <p>When large particles travel off their streamlines and bump into media grains</p> Signup and view all the answers

    Why is Brownian diffusion considered important in water treatment filtration?

    <p>It captures very small particles like viruses</p> Signup and view all the answers

    What is the maximum loss of head, in meters, allowed for a standard design of Rapid Sand filter?

    <p>2 to 5</p> Signup and view all the answers

    In the Rapid Sand filter design problem, what is the total filtered water in million liters per hour?

    <p>0.42766</p> Signup and view all the answers

    What is the area of the filter in square meters for the Rapid Sand filter design problem?

    <p>85.5</p> Signup and view all the answers

    How many lateral numbers are there in the Rapid Sand filter design with a given bed area?

    <p>25</p> Signup and view all the answers

    What is the diameter of the manifold in centimeters for the Rapid Sand filter design?

    <p>66</p> Signup and view all the answers

    What is the number of holes per lateral based on the calculations for the Rapid Sand filter design?

    <p>13</p> Signup and view all the answers

    What is the spacing of holes in centimeters for the Rapid Sand filter design?

    <p>19.5</p> Signup and view all the answers

    What is the velocity of flow through lateral in meters per second for the Rapid Sand filter design?

    <p>2.08</p> Signup and view all the answers

    What is the discharge of washwater per bed in cubic meters per second for the Rapid Sand filter design?

    <p>0.36</p> Signup and view all the answers

    What is the size of the bed in meters for the Rapid Sand filter design?

    <p>7.5 x 5.75</p> Signup and view all the answers

    What is the initial loss of head for a Slow Sand Filter (SSF) when cleaning is required?

    <p>10 cm</p> Signup and view all the answers

    What is the final limit for head loss in a Rapid Sand Filter (RSF) when cleaning is required?

    <p>2.5 to 3.5 m</p> Signup and view all the answers

    Which equation is used to calculate head loss in porous media according to the text?

    <p>$h = f(1-n)Lv_s^2Φn^3dg$</p> Signup and view all the answers

    What phenomenon is described as 'Air Binding' in the context of filter operation?

    <p>Negative pressure causing air bubbles to stick to sand grains</p> Signup and view all the answers

    What is the consequence of long filter runs according to the text?

    <p>Difficulty in expanding the filter bed during backwash</p> Signup and view all the answers

    Why are long filter runs not recommended in rapid sand filters?

    <p>To prevent filter media from packing down</p> Signup and view all the answers

    What is the main reason behind the phenomenon known as 'Formation of Mud Balls'?

    <p>Inadequate washing leading to sinking of mud into sand bed</p> Signup and view all the answers

    What problem arises when the frictional resistance by the filter media exceeds the static head of water, causing bubbles to stick to sand grains in filters?

    <p>Air Binding</p> Signup and view all the answers

    What does the uniformity coefficient in sand filters measure?

    <p>The variation in sizes of particles</p> Signup and view all the answers

    What is anthrafilt made from?

    <p>Anthracite</p> Signup and view all the answers

    What is the purpose of gravel in supporting sand layers in filters?

    <p>To allow filtered water to move freely</p> Signup and view all the answers

    How are slow sand filters usually cleaned?

    <p>By scraping away the top layer of sand</p> Signup and view all the answers

    Why does water pass through the filter skin and filter bed sand in the slow sand filter?

    <p>To remove impurities including bacteria and viruses</p> Signup and view all the answers

    What is the main difference in base material size and depth between slow sand filters and rapid sand filters?

    <p>Size: 3 to 65 mm; Depth: 30 to 75 cm</p> Signup and view all the answers

    What is the primary difference in filter sand between slow sand filters (SSF) and rapid sand filters (RSF)?

    <p>RSF has a larger effective size than SSF</p> Signup and view all the answers

    What is the process of killing harmful disease-producing bacteria in water to make it safe for drinking known as?

    <p>Sterilization</p> Signup and view all the answers

    Which equation represents the reduction in microorganisms when a single unit of microorganism is exposed to a single unit of disinfectant?

    <p>$dN/dt = -kN$</p> Signup and view all the answers

    Why is it not practical to use boiling as the primary method for large-scale water disinfection?

    <p>Boiling requires too much energy.</p> Signup and view all the answers

    What happens when lime is added in excess to water during the disinfection process?

    <p>It increases the water's alkalinity.</p> Signup and view all the answers

    Which method involves the breakdown of ozone into normal oxygen to aid in water disinfection?

    <p>Treatment with Ozone</p> Signup and view all the answers

    What is the primary reason recarbonation is recommended after using lime in water treatment?

    <p>To remove excess lime</p> Signup and view all the answers

    What is the total available head at the treatment plant as described in the text?

    <p>The difference in water surface elevations in the influent of first treatment unit and that in the effluent of last treatment unit</p> Signup and view all the answers

    What does the total loss through the connecting pipings, channels, and appurtenances include as mentioned in the text?

    <p>Head loss due to entrance, exit, contraction, friction, bends, fittings, gates, valves, meters, required head over weir, and free-fall surface allowance</p> Signup and view all the answers

    What is considered when preparing hydraulic profiles through the treatment plant according to the text?

    <p>Prepared for all main paths of flow through the plant at peak and average design flows</p> Signup and view all the answers

    Which of the following is NOT a component of head losses through the treatment unit as listed in the text?

    <p>Miscellaneous and free fall surface allowance</p> Signup and view all the answers

    What is one of the basic principles listed when preparing hydraulic profiles through the plant?

    <p>Preparation for peak and average design flows as well as minimum initial flow</p> Signup and view all the answers

    Why is pumping needed in cases where total available head is less than head loss through the plant?

    <p>To raise head so that flow by gravity can occur</p> Signup and view all the answers

    What is the primary function of nascent oxygen in water treatment?

    <p>React with organic and inorganic matter</p> Signup and view all the answers

    What is the main theory behind the germicidal action of chlorine in water treatment?

    <p>Enzymatic hypothesis</p> Signup and view all the answers

    Which compound is formed when ammonia reacts with chlorine in water treatment?

    <p>Monochloramine</p> Signup and view all the answers

    What is the composition of the free chlorine residual in water treatment?

    <p>Hypochlorous acid and hypochlorite ion</p> Signup and view all the answers

    What is the effect of excess free chlorine in water treatment after ammonia nitrogen is converted to monochloramine?

    <p>Breakpoint reactions oxidizing chloramine species</p> Signup and view all the answers

    What happens during the Monochloramine Formation Reaction in water treatment?

    <p>Ammonia nitrogen combined with free chlorine</p> Signup and view all the answers

    What does the term 'chlorine demand' refer to in water treatment?

    <p>The increase in chlorine requirement due to oxidation reactions</p> Signup and view all the answers

    How does chlorination help remove bacteria from water sources?

    <p>By killing essential enzymes of bacteria</p> Signup and view all the answers

    What is formed when hypochlorous acid dissociates in water?

    <p>Hypochlorite ion and hydrogen gas</p> Signup and view all the answers

    What is the significance of the breakpoint reactions in water treatment?

    <p>To remove excess free chlorine after chloramine formation</p> Signup and view all the answers

    Study Notes

    Filtration

    • The resultant water after sedimentation may still contain suspended particles and bacteria, which are removed through filtration.
    • Filtration is the process of passing water through beds of fine granular material, such as sand.

    Filtration Mechanisms

    • There are four basic filtration mechanisms:
      • Sedimentation: due to force of gravity and the associate settling velocity of the particle.
      • Interception: large particles follow the streamline and hit the media grain.
      • Brownian Diffusion: small particles (e.g. viruses) move randomly and collide with media grains.
      • Inertia: larger particles move fast enough to travel off their streamlines and bump into media grains.

    Filter Materials

    • Sand is commonly used as a filter media, with its size measured by effective size.
    • Other materials used include anthrafilt, gravel, and multimedia filters.

    Rapid Sand Filter Design

    • Design involves calculating the area of filter, depth of sand, and other parameters.
    • The design must consider factors such as backwashing, filtration rate, and head loss.

    Backwashing of Rapid Sand Filter

    • Backwashing is necessary to clean the filter and prevent clogging.
    • The filter should be backwashed when:
      • Head loss is too high.
      • Floc starts to break through the filter.
      • A filter run reaches a given hour of operation.

    Operational Troubles in Rapid Gravity Filters

    • Air Binding: the formation of bubbles in the filter due to negative pressure.
    • Formation of Mud Balls: the accumulation of mud on the sand surface, which can sink into the sand bed and cause problems.
    • Cracking of Filters: the development of shrinkage cracks in the sand bed due to increased pressure.

    Slow Sand Filter vs. Rapid Sand Filter

    • Differences in base material, filter sand, rate of filtration, and flexibility.
    • Slow sand filters are suitable for treating waters with low colors, low turbidities, and low bacterial contents.

    Disinfection

    • Disinfection is the process of killing harmful bacteria in water.
    • Methods of disinfection include:
      • Boiling.
      • Treatment with excess lime.
      • Treatment with ozone.
      • Other methods such as chlorination, ultraviolet (UV) light, and ultrasonic disinfection.

    Treatment Plant Hydraulics

    • Hydraulic profile is a graphical representation of the hydraulic grade line through the treatment plant.

    • Head loss computations are started in the direction of flow using the water surface in the influent of the first treatment unit as the reference level.

    • The total available head at the treatment plant is the difference in water surface elevations in the influent of the first treatment unit and that in the effluent of the last treatment unit.### Water Treatment

    • Nascent oxygen is a powerful oxidizing agent that removes organic matter and bacteria from water.

    Chlorination

    • Chlorine has a germicidal effect, which is explained by the enzymatic hypothesis, where chlorine enters bacterial cell walls and kills essential enzymes for metabolic processes.
    • Chlorine is added to water supply in two forms: gas (Cl2) and salt (sodium hypochlorite, NaOCl, or bleach).
    • Chlorine gas dissolves in water according to Henry's Law, with a constant of 6.2 x 10-2.
    • Dissolved chlorine reacts with water to form hypochlorous acid (HOCl), which dissociates to form hypochlorite ion (OCl-).

    Chlorine Reactions

    • Hypochlorous acid and hypochlorite ion compose the free chlorine residual.
    • Free chlorine residual can react with organic and inorganic compounds to form chlorinated compounds.
    • Chlorine reacts with ammonia to form chloramines, mainly monochloramine (NH2Cl), with excess free chlorine converting monochloramine to nitrogen gas.
    • The breakpoint reaction occurs when excess free chlorine is added, oxidizing chloramine species.

    Chlorine Demand

    • Free chlorine and chloramines react with various compounds, including organics and inorganics like iron and manganese.
    • The stoichiometry of chlorine reactions with organics can be represented by specific equations.
    • Chlorine demand increases with oxidation reactions with inorganics, such as reduced iron at corrosion sites.

    Treatment Plant Layout and Siting

    • Plant layout involves arranging treatment units on the selected site.
    • Siting involves selecting a site based on features like character, topography, and shoreline.
    • Important principles to consider in site development include using gravity flow, preserving natural site contours, and reflecting the surrounding area's character.

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    Description

    Learn about water filtration processes and mechanisms including the importance of filtration after sedimentation. Explore the four basic filtration mechanisms to understand how filters work effectively.

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