MP

Week5-2

Sludge Treatment Processes

  • Thickening: Water removal from sludge to increase solid concentration.

  • Digestion: Inactivation of pathogens and control of odors through microbial processes.

  • Conditioning: Treatment to improve dewatering, often using alum and high temperatures (175-230°C).

  • Dewatering: Further reduction of water content, contributing to pathogen inactivation.

  • Incineration: Reduces volume and weight of sludge, effectively managing waste.

  • Final Disposal: Safe disposal methods after treatment processes.

Filtration

  • Overview: Process involves passing water through granular material for purification.

  • Types of Filtration:

    • Slow Sand Gravity Filter: Works through gravity and slow filtration rates.

    • Rapid Sand Gravity Filter: Faster filtration, usually with coarser sand.

    • Pressure Filter: Uses pressure to force water through the filter medium.

Methods of Disinfection

  • Physical Methods:

    • Heat: Boiling water effectively kills bacteria.

    • U.V. Rays: Uses ultraviolet light to disinfect water.

  • Chemical Methods:

    • Oxidizing Chemicals: Chemicals that can kill pathogens.

    • Metal Ions: Certain metal ions can have disinfecting properties.

    • Alkalis and Acids: Utilized for their chemical effects on pathogens.

  • Minor Methods:

    • Boiling water, treatment with excess lime, ozone, iodine, bromine, potassium permanganate, and UV rays.

Disinfection Process

  • Definition: Killing harmful bacteria in filtered water to make it safe for drinking.

  • Objective: Ensure water is free of disease-causing microorganisms.

Methods of Disinfection

  • Boiling: Long boiling times destroy bacteria.

  • Treatment with Excess Lime: Lime softens water and can also kill bacteria if added in excess.

  • Treatment with Ozone: Ozone decomposes into oxygen, which is a strong oxidizer removing organic matter and bacteria.

  • Chlorination: Chlorine destroys bacteria by entering cell walls and disrupting metabolic processes.

Combined Residual vs. Free Residual Chlorine

  • Free Residual Chlorine:

    • Remains available for disinfection after reacting with contaminants.

    • More effective against bacteria and viruses due to rapid action.

  • Combined Residual Chlorine:

    • Forms chloramines after reacting with organic materials.

    • Less effective but offers longer residual protection.

  • Key Differences:

    • Free residual has a quicker action, while combined residual lasts longer.

Factors Affecting Disinfection Rates

  1. Concentration of Disinfectant: Higher concentrations enhance disinfection rates.

  2. Contact Time: Longer contact times improve efficiency.

  3. Temperature: Increased temperatures accelerate reactions.

  4. pH: Lower pH enhances chlorine effectiveness, maintaining it as hypochlorous acid.

  5. Microorganism Types: Resistant microorganisms (like protozoa) require more disinfectant.

Water Softening

  • Definition: Hard water contains high levels of calcium and magnesium bicarbonates, carbonates, sulfates, and chlorides.

  • Types of Hardness:

    • Temporary Hardness: Caused by bicarbonates of calcium and magnesium.

    • Permanent Hardness: Caused by sulfates and chlorides of various metals.

Removal of Hardness

  • Temporary Hardness Removal:

    1. Boiling

    2. Adding lime

  • Additional Methods for Temporary Hardness: 3. Lime-soda process 4. Zeolite process 5. Deionization or Demineralization process.

Adsorption Basics

  • Definition: A process where atoms/molecules adhere from a bulk phase onto a solid or liquid surface.

  • Adsorbate: The substance that is adsorbed.

  • Adsorbent: The surface that adsorbates adhere to.

Adsorption Principle

  • Surface Phenomenon: Result of surface energy due to strain and unbalanced forces at the surface.

  • Attraction and Retention: Surfaces attract and hold molecular species they contact.

Types of Adsorption

  • Physical Adsorption (Physisorption):

    • Unselective, lower energy of adsorption.

  • Chemical Adsorption (Chemisorption):

    • Selective, high energy of adsorption, reliant on gas and solid surface interactions.

Factors Affecting Adsorption

  • Temperature

  • Pressure

  • Surface Area

  • Activation of Solid Adsorbent

  • Agitation

  • pH

  • Adsorbent Characteristics

  • Dose of Adsorbate & Adsorbent

Commercial Adsorbents

  • Activated Carbon

  • Silica Gel

  • Activated Alumina

  • Synthetic Zeolite

  • Clay Polymers & Resins

Manufacture of Activated Carbon from Coal

  • Methodology: Production techniques involved in creating activated carbon.

Activated Carbon Variants

  • Granular Activated Carbon (GAC):

    • Larger particles (0.5 - 4 mm), slower adsorption but longer contact time.

  • Powdered Activated Carbon (PAC):

    • Fine powder (<0.1 mm), mixed in water for rapid adsorption and requires separation.

Adsorption Isotherm & Its Types

  • Definition: Models displaying solute distribution between solid and liquid phases at equilibrium.

  • Types:

    • Langmuir Isotherm: Assumes each site is singly occupied, constant energy of adsorption.

    • Freundlich Isotherm: Accounts for molecular interactions and energy surface heterogeneity.

Waste Water Treatment Techniques

  • Ion-Exchange

  • Adsorption:

    • Activated Carbon adsorbents

    • Carbon nanotubes

    • Low-cost adsorbents

    • Bioadsorbents

  • Membrane Filtration:

    • Ultrafiltration

    • Reverse Osmosis

    • Nanofiltration

    • Electrodialysis

  • Coagulation & Flocculation

  • Flotation

  • Electrochemical Treatment

Applications of Adsorption

  • Effective in heterogeneous catalysis.

  • Removing coloring materials.

  • Used in ion exchange resins.

  • Employed as adsorption indicators.

  • Utilized in gas masks.

  • Involved in dyeing processes.

  • Acts as de-humidifiers.