Hygienic evaluation of water purification and disinfection methods. Water pollution and self-purification.
1. Water Availability
- Only 2–3% of the world’s water is fresh and suitable for consumption.
- Ensuring safe drinking water requires purification and disinfection.
2. Water Pollution
- Definition: Contamination by biological, chemical, or physical agents, making water unsafe.
- Sources:
- Biological: Sewage, pathogens (bacteria, viruses, protozoa, helminths)
- Chemical: Industrial wastes, heavy metals, pesticides, detergents
- Physical: Sediment, trash, temperature changes
- Health Impact: Waterborne diseases (cholera, dysentery, hepatitis A, amoebiasis); indirect effects via contaminated food (fish, crops).
3. Self-Purification of Water
- Definition: Natural processes by which water bodies reduce pollution and restore quality.
- Mechanisms:
- Physical: Sedimentation (settling of suspended particles) and dilution (reduction of pollutant concentration).
- Chemical: Oxidation (breakdown of pollutants by chemical reactions), neutralization (balancing pH), and precipitation (conversion of dissolved substances into solids).
- Biological: Microbial decomposition of organic matter and transformation of toxic compounds into harmless forms.
- Importance: Maintains ecological balance and reduces burden on artificial treatment.
4. Water Treatment Steps
A. Purification – Removal of suspended and colloidal particles
- Coagulation: Chemicals such as aluminum sulfate or iron salts (15–20 mg/L) are added to aggregate fine particles.
- Sedimentation: Aggregated particles settle naturally or in sedimentation tanks.
- Filtration: Removes remaining particles.
- Active filters: Activated carbon; removes taste, odor, and certain chemicals.
- Passive filters: Sand or gravel; removes suspended solids.
- For advanced Purification:
- Reverse Osmosis (RO): Forces water through a semipermeable membrane; removes dissolved salts and some microbes.
B. Disinfection – Inactivation of pathogenic microorganisms
- Chemical methods: include the use of chlorine, ozone, hydrogen peroxide, or iodine tablets.
- Physical methods: UV radiation, ultrasound, boiling.
- Chlorination notes:
- Effective and inexpensive: residual chlorine protects against recontamination.
- Disadvantages: can produce disinfection by-products (DBPs) which may be carcinogenic (chlorite or chlorate); may affect taste/odor.
- Residual chlorine: Small amount of chlorine left after disinfection.
- Purpose: Maintains microbial safety during distribution through pipes, tanks, and storage.
- Typical concentration: ~0.2–0.5 mg/L—enough to kill microbes without affecting taste.
- Advantages: Continuous microbial protection; prevents outbreaks from leaks or contamination.
- Monitoring: Regular measurement ensures water safety.
C. Conditioning – Adjustment of water properties
- Adjust pH, control corrosion, and improve taste.
5. Hard vs. Soft Water
- Hard Water: High Ca²⁺ and Mg²⁺
- Forms scale; increases soap use
- Mg may protect heart; excess Ca may cause kidney stones
- Soft Water: Low Ca²⁺ and Mg²⁺
- Can be more corrosive to pipes
- For general health, moderately hard water is usually preferable because it provides essential minerals like calcium and magnesium.