Water and its Treatment

Water and Its Treatment: A Comprehensive Guide

Water is an essential resource for all forms of life, industrial processes, and domestic usage. However, its quality is often affected by the presence of dissolved minerals and impurities. One of the most common issues is water hardness, which affects household appliances, industrial machinery, and even drinking water quality. In this article, we will explore the concept of water hardness, its causes, types (temporary and permanent), expression, and measurement units.

Introduction to Water and Its Treatment

Importance of Water

Water is a universal solvent that plays a crucial role in various biological, industrial, and domestic activities. However, untreated water contains dissolved salts, gases, and suspended impurities, which can affect its usability.

What is Water Hardness?

• Water hardness refers to the presence of dissolved minerals, primarily calcium (Ca²⁺) and magnesium (Mg²⁺) ions.
  
• Hard water forms scales in pipes, reduces the effectiveness of soaps and detergents, and can cause industrial equipment failure.
  

Causes of Hardness in Water

Hardness in water originates from natural sources such as underground rocks, soil, and mineral deposits.

Common Causes of Water Hardness

• Limestone (CaCO₃) and Dolomite (CaMg(CO₃)₂): These minerals dissolve in water, releasing calcium and magnesium ions.
  
• Gypsum (CaSO₄·2H₂O): Dissolves in water and contributes to permanent hardness.
  
• Geothermal and Volcanic Activity: Hot water sources dissolve minerals, increasing water hardness.
  

Effects of Hard Water

• Reduces soap lathering: Soap reacts with calcium/magnesium to form scum instead of foam.
  
• Scale formation in pipes and boilers: Leads to blockages and decreased efficiency in industrial machinery.
  
• Affects textile and leather industries: Hard water interferes with dyeing and fabric processing.
  

Types of Hardness in Water

Water hardness is categorized into two types:

• Temporary Hardness
  
• Permanent Hardness
  

Temporary Hardness

• Caused by bicarbonates of calcium (Ca(HCO₃)₂) and magnesium (Mg(HCO₃)₂).
  
• Can be removed by boiling, which precipitates calcium carbonate.
  

Reaction During Boiling

Permanent Hardness

• Caused by sulfates (CaSO₄, MgSO₄) and chlorides (CaCl₂, MgCl₂) of calcium and magnesium.
  
• Cannot be removed by boiling and requires chemical treatment.
  

Expression and Units of Hardness

Expression of Hardness

Hardness is expressed in terms of equivalent CaCO₃ concentration because calcium carbonate is a standard reference compound.

Units of Hardness

The hardness of water can be measured in various units:

Unit	Equivalent CaCO₃ (mg/L)	Definition
Parts per million (ppm)	1 ppm = 1 mg/L	Common in water analysis
Milligrams per liter (mg/L)	1 mg/L = 1 ppm	Standard unit used in chemistry
Degrees of hardness (°dH)	1 °dH = 10 mg/L	German hardness unit
Clark’s degree (°Clark)	1 °Clark = 14.3 mg/L	Used in the UK
French degree (°Fr or °fH)	1 °Fr = 10 mg/L	Used in France

Classification of Water Based on Hardness

Water is categorized based on its hardness levels:

Hardness Level	Concentration (mg/L or ppm)
Soft Water	0 – 60 ppm
Moderately Hard Water	61 – 120 ppm
Hard Water	121 – 180 ppm
Very Hard Water	>180 ppm

Summary

Key Aspect	Details
Definition	Hardness is caused by dissolved calcium and magnesium ions in water.
Causes	Presence of Ca²⁺ and Mg²⁺ ions from minerals like limestone and gypsum.
Types	1. Temporary Hardness (Caused by bicarbonates, removed by boiling).2. Permanent Hardness (Caused by sulfates and chlorides, needs chemical treatment).
Effects	Scale formation, reduced soap efficiency, damage to industrial equipment.
Measurement	Expressed in ppm, mg/L, degrees of hardness (°dH, °Fr, °Clark).
Classification	Soft (0-60 ppm), Moderately Hard (61-120 ppm), Hard (121-180 ppm), Very Hard (>180 ppm).

This comprehensive guide provides a clear understanding of water hardness, its causes, types, and methods of expression. Understanding these aspects is crucial for industrial applications, household usage, and water treatment processes. 

Estimation of Hardness of Water by Complexometric Method & Potable Water Specifications

Water hardness affects its usability in domestic, industrial, and laboratory settings. One of the most reliable methods for determining water hardness is the complexometric titration method using EDTA (Ethylenediaminetetraacetic acid). This article explores the complexometric method of hardness estimation and the specifications of potable water.

Estimation of Hardness of Water by Complexometric Method

Introduction

Hardness in water is caused by dissolved salts of calcium (Ca²⁺) and magnesium (Mg²⁺). These ions interfere with detergents, cause scaling in pipelines, and affect industrial processes. The complexometric titration method using EDTA is a widely used technique to determine the total hardness of water.

Principle of Complexometric Titration

• EDTA (Ethylenediaminetetraacetic acid) is a chelating agent that forms stable, colorless complexes with Ca²⁺ and Mg²⁺ ions.
  
• Eriochrome Black T (EBT) is used as an indicator. It forms a pink complex with Ca²⁺ and Mg²⁺ ions in hard water.
  
• When EDTA is added, it binds to these metal ions, causing the solution to turn from wine-red to blue, indicating the endpoint of titration.
  

Chemical Reactions Involved

• Formation of metal-indicator complex (initial pink color)
  
• Titration with EDTA (complex formation, blue endpoint)
  

Materials Required

• Standard EDTA solution
  
• Hard water sample
  
• Eriochrome Black T (EBT) indicator
  
• Ammonia buffer solution (NH₄Cl/NH₄OH, pH ~ 10)
  
• Burette, pipette, conical flask, distilled water
  

Procedure

• Preparation of EDTA Solution
  
  • A standard 0.01M EDTA solution is prepared.
    
• Sample Preparation
  
  • Take 50 mL of the hard water sample in a conical flask.
    
• Buffer Addition
  
  • Add 5 mL of ammonia buffer (pH 10) to maintain alkalinity.
    
• Indicator Addition
  
  • Add a few drops of Eriochrome Black T (EBT) indicator.
    
  • The solution turns pink due to the Ca²⁺ and Mg²⁺ ions.
    
• Titration with EDTA
  
  • Fill the burette with 0.01M EDTA solution.
    
  • Titrate until the solution changes from pink to blue.
    
  • Record the burette reading at the endpoint.
    
• Calculation of Hardness
  
  • Hardness (mg/L of CaCO₃) is calculated using:
    

Where:

• V1​ = Volume of EDTA used (mL)
  
• M1​ ​ = Molarity of EDTA solution (mol/L)
  
• V2 ​ = Volume of water sample (mL)
  

Interpretation of Results

Hardness Level	CaCO₃ Concentration (mg/L)
Soft Water	0 – 60 mg/L
Moderately Hard Water	61 – 120 mg/L
Hard Water	121 – 180 mg/L
Very Hard Water	>180 mg/L

Potable Water and Its Specifications

What is Potable Water?

Potable water is safe drinking water that is free from harmful contaminants such as bacteria, viruses, heavy metals, and excessive mineral content. It should be colorless, odorless, tasteless, and free from toxic substances.

Characteristics of Potable Water

1. Physical Characteristics
   
   • Color: Clear and transparent.
     
   • Odor & Taste: Should be pleasant and free from foul smells.
     
   • Turbidity: Should be less than 5 NTU (Nephelometric Turbidity Units).
     
2. Chemical Characteristics
   
   • pH: Between 6.5 – 8.5 (as per WHO standards).
     
   • Total Dissolved Solids (TDS): Below 500 mg/L.
     
   • Hardness: Below 300 mg/L as CaCO₃.
     
   • Chloride (Cl⁻): Below 250 mg/L.
     
   • Nitrate (NO₃⁻): Below 50 mg/L.
     
3. Biological Characteristics
   
   • Free from bacteria, viruses, and pathogens such as E. coli and Salmonella.
     
   • Should not contain algae or fungi growth.
     

Treatment Methods for Potable Water

To make water potable, various treatment methods are used:

1. Filtration

• Removes suspended particles and microorganisms.
  

2. Coagulation and Flocculation

• Chemicals like alum (Al₂(SO₄)₃) are added to remove fine particles.
  

3. Sedimentation

• Allows heavy particles to settle.
  

4. Disinfection

• Chlorination (Adding Cl₂ gas) kills pathogens.
  
• UV Treatment destroys bacteria and viruses.
  
• Ozonation oxidizes contaminants.
  

5. Reverse Osmosis (RO)

• Used to remove dissolved salts and heavy metals.
  

6. Desalination

• Used in coastal regions to remove salt from seawater.
  

WHO Standards for Drinking Water

Parameter	WHO Standard (mg/L)
pH	6.5 – 8.5
TDS	< 500 mg/L
Hardness	< 300 mg/L
Chloride (Cl⁻)	< 250 mg/L
Nitrate (NO₃⁻)	< 50 mg/L
Fluoride (F⁻)	< 1.5 mg/L
Iron (Fe²⁺)	< 0.3 mg/L
Lead (Pb²⁺)	< 0.01 mg/L

Summary

Topic	Details
Hardness Estimation	Determined using EDTA titration method.
Principle	EDTA forms a colorless complex with Ca²⁺ and Mg²⁺ ions, causing a color change from pink to blue.
Indicator Used	Eriochrome Black T (EBT)
Calculation Formula
Potable Water	Safe for drinking, free from harmful microbes and contaminants.
Treatment Methods	Filtration, Coagulation, Sedimentation, Disinfection, RO, Desalination.
WHO Standards	pH: 6.5 – 8.5, Hardness: < 300 mg/L, TDS: < 500 mg/L.

Water Treatment: Steps, Disinfection, and Industrial Water Treatment

Water treatment is a systematic process used to make water suitable for drinking, industrial use, and domestic applications. It involves multiple physical, chemical, and biological steps to remove contaminants, microorganisms, and dissolved impurities. This article covers:

• Steps involved in water treatment
  
• Disinfection methods: Chlorination & Ozonization
  
• Industrial water treatment: Boiler feed water treatment
  
• Internal conditioning methods: Calgon & Phosphate conditioning
  

Steps Involved in Water Treatment

Screening

• Removes large debris, leaves, twigs, plastics, and other solid particles using metal screens.
  
• Prevents damage to pumps and pipes in the treatment process.
  

Coagulation & Flocculation

• Coagulation:
  
  • Chemicals like Alum (Al₂(SO₄)₃), Ferric chloride (FeCl₃) are added to destabilize suspended particles.
    
  • Causes small impurities to stick together.
    
• Flocculation:
  
  • Slow mixing helps form larger particles called flocs.
    
  • Improves sedimentation efficiency.
    

1.3 Sedimentation

• Large flocs settle at the bottom of the tank.
  
• Clear water is separated and moved for further treatment.
  

Filtration

• Sand Filters & Activated Carbon Filters remove fine particles, organic matter, and microbes.
  
• Membrane filtration (Reverse Osmosis, Ultrafiltration) removes dissolved salts & bacteria.
  

Disinfection

• Final stage to kill bacteria, viruses, and pathogens.
  
• Common methods: Chlorination & Ozonization (discussed below).
  

Disinfection of Water

Chlorination

• Chlorine gas (Cl₂) or bleaching powder (Ca(OCl)₂) is added to water to kill microbes.
  
• It oxidizes bacteria and viruses, making water safe for drinking.
  

Chemical Reactions

• When chlorine reacts with water:
  
  (Hypochlorous acid (HOCl) is the active disinfectant.)
  
• Alternative chlorination method using bleaching powder:
  

Advantages of Chlorination

 Kills bacteria and viruses effectively.
  Cost-effective and easy to implement.
  Provides long-lasting residual protection.

Disadvantages

 Forms harmful chlorinated byproducts (e.g., trihalomethanes, which are carcinogenic).
  Less effective against some viruses and parasites.

Ozonization (Ozone Disinfection)

• Uses ozone gas (O₃) to disinfect water.
  
• O₃ is a strong oxidizing agent that destroys bacteria, viruses, and organic pollutants.
  

Chemical Reaction

(Active oxygen destroys pathogens.)

Advantages of Ozonization

 Stronger disinfectant than chlorine.
  No harmful byproducts.
  Removes bad taste and odor.

Disadvantages

 Expensive and requires specialized equipment.
Ozone decomposes quickly, so no residual protection is available.

Industrial Water Treatment

Industries require high-purity water for boilers, cooling systems, and chemical processes. Impure water can lead to corrosion, scaling, and efficiency loss.

Boiler Feed Water & Its Treatment

• Boiler feed water must be free from:
  
  • Dissolved salts (cause scaling).
    
  • Dissolved oxygen (causes corrosion).
    
  • Hardness ions (Ca²⁺, Mg²⁺).
    

Methods of Boiler Feed Water Treatment

1. External Treatment (Pre-treatment before entering the boiler)
   
   • Softening: Removes Ca²⁺ and Mg²⁺ using ion-exchange resins.
     
   • Deaeration: Removes dissolved oxygen to prevent corrosion.
     
2. Internal Treatment (Chemical conditioning inside the boiler)
   
   • Prevents scaling, corrosion, and sludge formation.
     
   • Calgon & Phosphate conditioning are common internal treatment methods.
     

Internal Conditioning Methods

Calgon Conditioning

• Uses sodium hexametaphosphate (Na₆P₆O₁₈) to prevent scale formation.
  
• Reaction:
  
  (Prevents CaCO₃ precipitation.)
  

Advantages

 Converts hardness salts into soluble complexes.
  Prevents boiler scaling.
  Non-corrosive treatment method.

Disadvantages

 Requires constant dosage adjustment.

Phosphate Conditioning

• Uses sodium phosphate (Na₃PO₄) to convert hardness salts into soft sludge.
  

Chemical Reaction

Advantages

 Converts hard scales into soft, non-adherent sludge.
  Cheap and effective.
  Controls corrosion and pH.

Disadvantages

 Sludge needs regular removal to prevent boiler blockages.

Summary Table

Topic	Key Points
Water Treatment Steps	Screening → Coagulation → Sedimentation → Filtration → Disinfection
Chlorination	Uses Cl₂ or Ca(OCl)₂ to kill microbes (cheap but forms byproducts).
Ozonization	Uses O₃ for stronger disinfection (no byproducts, but expensive).
Boiler Feed Water Treatment	Removes salts, gases, and hardness to prevent scaling and corrosion.
Calgon Conditioning	Uses Na₆P₆O₁₈ to form soluble complexes with Ca²⁺.
Phosphate Conditioning	Uses Na₃PO₄ to convert Ca²⁺ into soft sludge.

External Treatment of Water: Ion Exchange Process & Desalination (Reverse Osmosis)

Water used in industries, power plants, and households must be free from hardness, salts, and impurities to prevent corrosion, scaling, and inefficiencies. The external treatment of water focuses on removing dissolved solids, hardness ions (Ca²⁺, Mg²⁺), and other contaminants before it enters industrial processes.

This article covers:

• Ion Exchange Process for Water Softening
  
• Desalination of Water (Reverse Osmosis)
  

External Treatment of Water

External treatment is a pre-treatment process used to remove dissolved impurities, hardness ions, and dissolved salts before the water is used in industries, boilers, or drinking purposes.

Importance of External Water Treatment

 Prevents boiler scaling and corrosion.
  Reduces total dissolved solids (TDS) in water.
  Enhances efficiency of industrial processes.
  Makes water potable and suitable for drinking.

One of the most common external treatment methods is the Ion Exchange Process, which is used to soften hard water.

Ion Exchange Process for Water Softening

The Ion Exchange Process removes dissolved hardness-causing ions (Ca²⁺, Mg²⁺, Fe²⁺) and replaces them with non-scaling ions (Na⁺, H⁺, OH⁻).

Principle of Ion Exchange

• The process involves ion-exchange resins, which are synthetic polymers with active ion-exchange sites.
  
• These resins selectively replace unwanted ions in water with desired ions.
  

There are two types of ion-exchange resins:

1. Cation Exchange Resins (remove Ca²⁺, Mg²⁺, Fe²⁺).
   
2. Anion Exchange Resins (remove Cl⁻, SO₄²⁻, NO₃⁻).
   

Ion Exchange Reactions

Step 1: Softening of Water (Removal of Ca²⁺ & Mg²⁺ using Cation Exchange Resins)

• Resin used: Sodium-based resin (R-Na⁺).
  
• Reaction:
  
  (The resin captures Ca²⁺ and Mg²⁺, releasing Na⁺ into water.)
  

Step 2: Removal of Anions (Using Anion Exchange Resins)

• Resin used: Hydroxide-based resin (R-OH⁻).
  
• Reaction:
  
  (The resin removes Cl⁻ and SO₄²⁻, releasing OH⁻ ions.)
  

Regeneration of Resins

• Over time, resins get exhausted (i.e., they become saturated with Ca²⁺, Mg²⁺, and Cl⁻).
  
• They must be regenerated using suitable reagents:
  
  • Cation Exchange Resins: Regenerated using NaCl solution (brine).
    
  • Anion Exchange Resins: Regenerated using NaOH solution.
    

Advantages of Ion Exchange Process

 Completely removes hardness.
  Can remove dissolved salts as well.
  Reusable resins reduce operational costs.
  Works for both industrial and potable water treatment.

Disadvantages

 Requires periodic regeneration.
  High initial investment cost.
  Cannot handle high TDS (saline water) effectively.

To remove high TDS and salt content, desalination methods like Reverse Osmosis (RO) are used.

Desalination of Water (Reverse Osmosis)

Desalination is the process of removing salts, minerals, and impurities from seawater or brackish water to make it suitable for drinking, irrigation, and industrial use.

Methods of Desalination

1. Thermal Desalination (Evaporation & Condensation)
   
2. Reverse Osmosis (RO) Desalination
   

Among these, Reverse Osmosis (RO) is the most widely used method due to its efficiency and cost-effectiveness.

Reverse Osmosis (RO) Process

Principle of Reverse Osmosis

• Osmosis is the movement of water molecules from a region of low solute concentration to a region of high solute concentration through a semi-permeable membrane.
  
• Reverse Osmosis applies high pressure to force water to move against the natural osmotic flow, removing salts and impurities.
  

RO Process: Step-by-Step

1. Pre-treatment: Removes suspended particles, chlorine, and organic matter to protect RO membranes.
   
2. High-Pressure Pump: Applies pressure (30-80 bar) to push water through the semi-permeable membrane.
   
3. RO Membrane Filtration: Allows pure water molecules to pass, while salts, bacteria, and contaminants are rejected.
   
4. Post-treatment: Adjusts pH and adds minerals to improve taste and quality.
   

RO Membrane Filtration Efficiency

 Removes 99% of dissolved salts.
  Eliminates bacteria, viruses, heavy metals.
  Produces pure, clean drinking water.

Advantages of Reverse Osmosis

 Highly effective for seawater desalination.
  Removes pathogens, salts, and toxic metals.
  Improves water taste and quality.

Disadvantages of Reverse Osmosis

 High energy consumption due to pressure requirement.
  Wastes 30-50% of input water as reject brine.
  Requires regular membrane maintenance.

Comparison of Ion Exchange & Reverse Osmosis

Feature	Ion Exchange	Reverse Osmosis
Removes Hardness?	Yes (Ca²⁺, Mg²⁺)	Yes
Removes Salts (TDS)?	No	Yes
Regeneration Required?	Yes (Resin regeneration)	No
Removes Microorganisms?	No	Yes
Energy Consumption	Low	High
Used For	Softening of Water	Desalination of Saline Water

Conclusion

 Ion Exchange Process is best for removing hardness (Ca²⁺, Mg²⁺) in industrial and boiler feed water.
  Reverse Osmosis (RO) is ideal for desalination (removing dissolved salts from seawater and brackish water).
  Both methods are widely used in potable water treatment, power plants, and industries.