Water Treatment Lecture 5: Quality Parameters and Treatment Processes

Human Rights and Global Water Governance

Recognition of Water as a Human Right:
- On 28 July 2010, the United Nations (UN) formally recognized the human right to water and sanitation.
- The UN acknowledged that access to clean drinking water and sanitation is fundamental and essential to the realization of all human rights.
Sustainable Development Goals (SDG):
- Sustainable Development Goal 6 (SDG 6) specifically targets "Achieving universal access to safely managed water and sanitation and appropriate management of water resources."
- The global deadline established for achieving these objectives is the year 2030.

Classification of Water Quality Parameters

Water quality is evaluated based on three primary categories of parameters:

Physical Parameters:
- Suspended Solids.
- Turbidity.
- Colour.
- Taste and Odour.
- Temperature.
Chemical Parameters:
- Dissolved Solids (Total Dissolved Solids - TDS).
- $\text{pH}$ (Acidity/Alkalinity).
- Alkalinity.
- Hardness ( $\text{Ca}^{2+}$ and $\text{Mg}^{2+}$ ).
- Chemical constituents such as Nitrogen, Chlorides, and Fluorides.
Biological Parameters:
- Bacteria.
- Helminths (parasitic worms).
- Viruses.
- Protozoa.

Detailed Physical Parameters

Suspended Solids (SS):
- Definition: Fine particles of sediment present in the water column.
- Examples: Soil, biological solids, decaying organic matter, and particles discharged through wastewater.
- Environmental Impact:
  - Increased sediment levels reduce water clarity.
  - Reduced clarity prevents light from penetrating the water surface to reach submerged plants.
  - The reduction in sunlight inhibits photosynthesis activity, leading to lower oxygen production.
  - This cycle can create hypoxic (low-oxygen) conditions and contribute to the formation of "dead zones."
Temperature:
- Temperature significantly influences the rate of chemical and biological reactions in water.
- Biological Impact: An increase of $10\,^{\circ}C$ effectively doubles the biological activity levels.
- Standard for Water Supply: For human consumption and general water supply, the temperature should ideally be maintained between $10\text{--}25\,^{\circ}C$ .

Detailed Chemical Parameters

Total Dissolved Solids (TDS):
- Definition: TDS represents the total concentration of dissolved substances within water.
- Composition: TDS is comprised of inorganic salts and small quantities of organic matter.
- Constituent Ions:
  - Cations (Positively Charged): Calcium ( $\text{Ca}^{2+}$ ), Magnesium ( $\text{Mg}^{2+}$ ), Potassium ( $\text{K}^{+}$ ), and Sodium ( $\text{Na}^{+}$ ).
  - Anions (Negatively Charged): Carbonates ( $\text{CO}_3^{2-}$ ), Nitrates ( $\text{NO}_3^{-}$ ), Bicarbonates ( $\text{HCO}_3^{-}$ ), Chlorides ( $\text{Cl}^{-}$ ), and Sulfates ( $\text{SO}_4^{2-}$ ).
The $\text{pH}$ Scale:
- Definition: The $\text{pH}$ value is a measure of the acidity or alkalinity of a water source.
- Neutrality: Pure water has a $\text{pH}$ of $7.0$ .
- Environmental Variability: Natural water sources and precipitation are often slightly acidic due to atmospheric and environmental contaminants.
- Pollution Impacts: Industrial operations and community waste can cause water bodies to become highly acidic through illegal discharges or inadequate treatment.
- The $\text{pH}$ Spectrum (0-14):
  - $0$ : Battery Acid.
  - $1$ : Stomach Acid.
  - $2$ : Lemon.
  - $3$ : Soda.
  - $4$ : Tomato.
  - $5$ : Black Coffee.
  - $6$ : Milk.
  - $7$ : Pure Water (Neutral).
  - $8$ : Blood.
  - $9$ : Egg White.
  - $10$ : Stomach Tablets.
  - $11$ : Ammonia Solution.
  - $12$ : Soap.
  - $13$ : Bleach.
  - $14$ : Drain Cleaner.
Water Hardness:
- Cause: Dissolved Calcium and Magnesium.
- Practical Implications:
  - Causes scaling in hot water systems, kettles, electric irons, and various domestic appliances.
  - Scaling Definition: Deposits of calcium and magnesium that accumulate on heating elements over time.
  - Effects of scaling include shortened appliance lifespan and reduced energy efficiency.
  - Hard water interferes with soap, resulting in significantly less lather from washing liquids and powders.
- Types of Hardness:
  1. Temporary Hardness: Caused by metal bicarbonates such as Calcium Bicarbonate ( $\text{Ca(HCO}_3)_2$ ) and Magnesium Bicarbonate ( $\text{Mg(HCO}_3)_2$ ).
  2. Permanent Hardness: Caused by sulfates, chlorides, and nitrates of calcium and magnesium. Examples include $\text{CaSO}_4$ , $\text{MgSO}_4$ , $\text{CaCl}_2$ , and $\text{MgCl}_2$ .

Water Softening and Treatment Processes

Softening Techniques:
- Temporary Hardness: Can be removed through physical or specific chemical interventions.
- Permanent Hardness: Frequently removed via the "Lime-Soda Softening" process.
  - Chemical Reaction: Addition of Lime ( $\text{Ca(OH)}_2$ ) and Sodium Carbonate ( $\text{Na}_2\text{CO}_3$ ).
  - Mechanism: These chemicals react with hardness compounds to force them to precipitate out of the water.

Wastewater Treatment Steps

1. Pretreatment

Screening: Used to remove grits and large physical impurities (e.g., using bar screens).
Oil and Grease Removal: Utilizes a process called "Flotation."
- Mechanism: Micro-bubbles of air are formed in the water. As these bubbles rise to the surface, they drag oil droplets and fat particles upward for removal.

2. Primary Treatment

Goal: To settle suspended solids; this stage typically removes approximately $60\%$ of Total Suspended Solids (T.S.S.).
Methods:
- Free settling (Gravity-based).
- Settling using Coagulants.
Coagulants used:
- Alum.
- Ferrous Sulfate ( $\text{FeSO}_4$ ).
- Ferric Chloride ( $\text{FeCl}_3$ ).
- Polyelectrolytes.
Coagulation Definition: A process that combines small particles into larger aggregates known as "flocs." It also adsorbs dissolved organic matter onto these aggregates to facilitate removal during sedimentation or filtration.

3. Biological (Secondary) Treatment

Definition: A method utilizing microorganisms to degrade organic compounds in the water effluent.
Modes: Can be performed Aerobically (with oxygen) or Anaerobically (without oxygen).

4. Disinfection

Definition: The destruction or inactivation of disease-causing (pathogenic) organisms.
Impact: Reduces the concentration of pathogenic constituents to an acceptable, safe level.
Common Disinfectants:
- Chlorine.
- Iodine.
- Ultraviolet (UV) Radiation.

Typical Wastewater Treatment Schematic

The sequence of a typical treatment plant involves the following flow:

Raw Wastewater Input.
Pretreatment: Bar Screening, Grit Removal, and Oil Removal.
Primary Treatment: Primary Clarifier / Sedimentation (Settling of Solids).
Secondary Treatment (Biological): Aeration tanks and Secondary Clarifier.
Tertiary Treatment: Advanced filtration or specialized removal.
Disinfection: Chlorination.
Final Effluent Discharge.
Sludge Handling: Sludge dewatering and eventual disposal.