Introduction to Water Chemistry
🌊 Importance of Water
- Essential ingredient of the environment
- Composes the hydrosphere
- Life processes impossible without water
- Basis of metabolic activities
- Essential for agriculture and industry
📝 Water Distribution:
• Oceanic (saltish) water: ~97% of total water
• Fresh water: ~3% (most in glaciers and ice caps)
🔍 Point vs Non-Point Sources
- Specific outlet/location
- Easy to identify and stop
- Examples: Industrial effluents, water treatment plants, oil spills
- Widespread, not specified
- Result of seepage/runoff
- Examples: Pesticides, fertilizers, construction, residential effluents
14.1 Sources of Water Pollution
⚠️ 1. Agricultural Pollutants
- Pesticides: Significant hazards to aquatic life
- Runoff: From treated fields to water bodies
- Impact: Fish, insects, ecosystems, food chain
- Fertilizers: Cause eutrophication
- Agriculture slush: From harvested fields
🛢️ 2. Oil Spillage
- Sources: Oil cargo ships, offshore exploration
- Effects: Destroys aquatic ecosystems
- Oil sheet: Stops aeration and light penetration
- Impact: Aquatic plants cannot survive
🚽 3. Sewage & Wastewater
- Untreated sewage causes bacterial pollution
- Pathogens cause serious diseases
- Proper treatment essential before discharge
⛏️ 4. Mining Activities
- Produces grit drained by rainwater
- Makes water bodies shallow and filthy
- Unfit for fisheries and general use
- Loss of aesthetic value
🏭 5. Industrial Pollution
- Heavy metals: Lead, mercury, cadmium
- Bioaccumulation: Accumulates in organisms
- Biomagnification: Increases up food chain
- Soil contamination: Affects plant growth
- Groundwater pollution: Long-term risks
💡 Key Fact: Industrial effluents are point sources while agricultural runoff are non-point sources of pollution.
14.2 Health Effects of Water Pollutants
🤒 Waterborne Diseases
- Cholera, diarrhoea, dysentery
- Hepatitis A, typhoid, polio
- Caused by contaminated water and poor sanitation
- Preventable with proper water management
☣️ Heavy Metal Toxicity
⚠️ Bioaccumulation: Heavy metals accumulate in body tissues over time, leading to chronic diseases including cancer.
14.5 Laws & Regulations
🌍 1. Kyoto Protocol (Worldwide)
- Focused on air pollution but includes water
- Measures to decrease emissions from deforestation
- Indirectly protects water resources
🇺🇸 2. Clean Water Act (USA)
- Primary federal law on water pollution
- Objective: Restore integrity of US waters
- Sets national drinking water standards
- Regulates public water systems
🇨🇳 3. Water Pollution Control Act (China)
- Sets water standards and monitoring procedures
- Funding permissions for industrial units
- Penalties for violations
🇵🇰 4. Pakistan’s Water Laws
- Pakistan Environmental Protection Act 1997: Legal framework for environment protection
- National Environmental Quality Standards (NEQS): Sets pollutant standards
- Pakistan Water Act 1998: Regulates water resource development and conservation
- Right to water: Ensures equal access to clean drinking water
14.4 Water Treatment Methods
💧 14.4.1 Raw Water Treatment
1. Screening
Remove debris, sticks, leaves
Remove debris, sticks, leaves
→
2. Coagulation
Alum (ferric/ammonium sulphate)
Alum (ferric/ammonium sulphate)
→
3. Sedimentation
12+ hours, sludge removal
12+ hours, sludge removal
4. Filtration
Sand, gravel, activated charcoal
Sand, gravel, activated charcoal
→
5. Disinfection
Chlorination, ozonation, UV
Chlorination, ozonation, UV
♻️ 14.4.2 Waste Water Treatment
- Primary: Screening & sedimentation
- Secondary: Biological processes (activated sludge)
- Tertiary: Advanced purification (nutrient removal)
- Disinfection: Killing pathogens
- Advanced Oxidation: Breaking persistent compounds
- Constructed Wetlands: Natural purification
🔬 Did You Know? Activated sludge process uses microorganisms to break down organic matter in wastewater.
14.3 Environmental Problems
🐟 Aquatic Life Impact
- Polluted water cannot support fisheries
- Aluminium ions form gelatinous hydroxide
- Clogs fish gills causing suffocation
- Surfactants, heavy metals, pesticides harmful
🌿 Eutrophication
- Excessive fertilizers drain into water
- Causes algal bloom (algae overgrowth)
- Oxygen depletion in water
- Can cause extinction of lakes/ponds
🚰 Contaminated Drinking Water
- Surface & groundwater vulnerable
- Bacteria & pathogens cause diseases
- Agriculture waste contributes
- Makes water unfit for drinking
🏞️ Habitat Destruction
- Coral reefs and wetlands destroyed
- Ecosystem destruction
- Loss of shoreline protection
- Reduced flood safeguard
14.7 Conservation Strategies
💡 Top 10 Conservation Strategies
- Smart Water Use: Efficient technologies in homes/industry
- Wastewater Treatment: Reuse purified water
- Rainwater Harvesting: For non-potable uses
- Watershed Protection: Erosion control, reforestation
- Water Recycling: Promote wastewater reuse
- Legislation: Enforce pollution control laws
- Public Awareness: Educate about water importance
- Desalination: For coastal cities
- Research & Technology: Innovative solutions
- International Cooperation: Transboundary water management
🌱 Sustainable Agriculture: Drip irrigation and sustainable methods can reduce agricultural water consumption by up to 60%.
14.8 Properties of Water Related to Pollution
🧪 Universal Solvent
- Polarity allows dissolution of many substances
- High dielectric constant
- Forms hydrogen bonds and ion-dipole forces
- High surface tension
- Greater density in liquid state
Rainwater Chemistry:
H₂O + CO₂ ⇌ H₂CO₃ (carbonic acid)
H₂CO₃ ⇌ H⁺ + HCO₃⁻
Converts insoluble carbonates to soluble bicarbonates
H₂O + CO₂ ⇌ H₂CO₃ (carbonic acid)
H₂CO₃ ⇌ H⁺ + HCO₃⁻
Converts insoluble carbonates to soluble bicarbonates
🔬 Solubility Characteristics
- Organic compounds soluble due to hydrogen bonding
- Alcohols, amines, carboxylic acids dissolve
- High surface tension allows microbes to walk on water
- Dissolves surfactants and soaps
- High heat capacity: absorbs industrial heat
💧 Water’s Unique Properties: Understanding water’s solvent properties is crucial for assessing pollution levels and designing treatment methods.
MCQs & Exercise Questions
MCQ 1: How much of the total water of the planet is present in the oceans?
MCQ 2: What type of pollutants can cause eutrophication?
MCQ 3: In which method are small particles coagulated into big particles and then separated?
MCQ 4: Which pollution can cause cancer?
MCQ 5: Disinfection of water is done by:
Question 2: Explain the distribution of water on the global level.
Answer: Global water distribution shows that 97% is oceanic (saltwater) and only 3% is freshwater. Of this freshwater:
- ~68.7% in glaciers and ice caps
- ~30.1% as groundwater
- ~0.3% in lakes and rivers
- ~0.9% in other sources (soil moisture, atmosphere, etc.)
This means less than 1% of all Earth’s water is readily available freshwater for human use.
Question 3: How raw water treatment is done for municipal water supply?
Answer: Raw water treatment for municipal supply involves:
Screening:
Remove large debris
Remove large debris
→
Coagulation:
Alum forms flocs
Alum forms flocs
→
Sedimentation:
Particles settle
Particles settle
Filtration:
Sand/charcoal filters
Sand/charcoal filters
→
Disinfection:
Kill pathogens
Kill pathogens
→
Distribution:
To consumers
To consumers
Question 5: Evaluate the strain on fresh water availability by agriculture and industry.
Answer: Agriculture and industry place significant strain on freshwater:
- Irrigation consumes vast amounts
- Pesticides/fertilizers pollute water
- Soil erosion reduces water quality
- Over-pumping depletes groundwater
- Cooling processes need large volumes
- Chemical pollutants contaminate water
- Thermal pollution affects ecosystems
- Heavy metals cause long-term damage
Combined impact: Reduces available clean water, affects ecosystems, and creates water scarcity.
Question 6: Suggest some measures to ensure the preservation of water reservoirs.
Answer: Measures for water reservoir preservation:
- Watershed management: Protect catchment areas
- Afforestation: Plant trees around reservoirs
- Pollution control: Strict regulations on discharges
- Regular monitoring: Water quality testing
- Sediment control: Prevent siltation
- Public awareness: Educate communities
- Riparian buffers: Vegetation along banks
- Eco-friendly agriculture: Reduce runoff
- Regular maintenance: Remove invasive species
- Legal protection: Designate protected areas
Question 7: Evaluate the impact of pollutants on ecosystem.
Answer: Pollutant impacts on ecosystems:
| Pollutant Type | Ecosystem Impact |
|---|---|
| Nutrients (Fertilizers) | Eutrophication → algal blooms → oxygen depletion → fish kills |
| Pesticides | Bioaccumulation → food chain disruption → species decline |
| Heavy Metals | Toxicity → reduced biodiversity → habitat degradation |
| Oil Spills | Coating organisms → suffocation → habitat destruction |
| Thermal Pollution | Temperature change → reduced oxygen → species migration |
| Sediments | Turbidity → reduced photosynthesis → habitat smothering |
Cumulative effect: Loss of biodiversity, ecosystem imbalance, reduced ecosystem services, and potential collapse of aquatic systems.
Project 1: Prepare a chart to highlight the waste water treatment.
Wastewater Treatment Chart:
Preliminary
Screening
Grit Removal
Screening
Grit Removal
→
Primary
Sedimentation
Sludge Removal
Sedimentation
Sludge Removal
→
Secondary
Biological
Treatment
Biological
Treatment
Tertiary
Advanced
Treatment
Advanced
Treatment
→
Disinfection
Chlorination
UV/Ozone
Chlorination
UV/Ozone
→
Discharge/Reuse
Safe for
Environment
Safe for
Environment
Key Processes: Activated Sludge, Trickling Filters, Nutrient Removal, Advanced Oxidation