MP

Filtration

Filtration

Overview

  • Filtration is a crucial process in conventional water treatment systems.

Components of Filtration

  • Oxidant/Disinfectant: Used to treat influent water before sedimentation.

  • pH Control: Adjusts water acidity for optimal coagulation.

  • Coagulants: Help in the aggregation of particles for easier removal.

  • Filter Aid/Polymer: Enhances filtration efficiency.

  • Influent: Originates from surface water, enters the treatment system.

  • Screening: First step in removing large particles from influent.

Filtration Process Steps

  1. Rapid Flocculation: Particles agglomerate.

  2. Sedimentation: Larger flocs settle to the bottom.

  3. Granular Filtration: Smaller particles are removed by passing water through gravel, sand or other media.

  4. Clearwell Storage: Treated water is stored before distribution.

  5. Filter Washwater: Wastes and byproducts are washed out.

  6. Waste Management: Involves processing solids and returning water for further treatment or disposal.

Packed Reactors

Definition

  • Packed reactors utilize media for filtration and adsorption processes.

Filtration Mechanisms

  • Straining/Sieving: Removes large particles by size.

  • Adhesion: Smaller particles adhere to the media surface.

  • Flocculation: Indicates the gathering of small particles into larger aggregates.

  • Sedimentation: Similar to standard filtration, where settled flocs are removed.

Particle Size Distribution

  • Effective Size (d10): Represents the size below which 10% of the particles lie.

  • Uniformity Coefficient (UC): Calculated as UC = d60 / d10, indicating the distribution range of particle sizes.

Representation of Distribution

  • Graphical representation shows percentage of particles and corresponding sizes, indicating effective filtration capabilities based on different sizes.

Headloss

Importance in Filtration

  • Physical Properties: Relate to how filter media affects flow, creating resistance.

  • Chemical Properties: Relate to the adsorption capacity of the media.

Breakthrough Curves

  • Graph illustrating the relationship between treated water volume and concentration changes, indicating when the filter reaches exhaustion.

Backwash Process

Functionality

  • Essential for maintaining filter media integrity. Techniques include:

  1. Water Filtering: Introduces water to cleanse the media.

  2. Air Valves: Enhance backwash efficiency.

  3. Control Valves: Regulate flow rates during the backwash.

Adsorption

Process Description

  • Transfer of substances from a liquid or gas phase to a solid surface.

Types of Adsorbents

  • Activated Carbon

    • Powdered Activated Carbon (PAC)

    • Granular Activated Carbon (GAC)

  • Synthetic Polymers: Varied materials used in specialized applications.

  • Silica-based Materials: Often used for filtration due to chemical inertness and stability.

Uptake of Contaminants

  • Expressed in terms of mass adsorbed over time to determine efficiency. The uptake can be modeled using isotherms, particularly the Freundlich isotherm, which represents the relationship between concentration and adsorption capacity.