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- Water scarcity affects 40% of the world's population.
- 1.8 billion people use a contanimated drinking water source.
- About one-third of the World's population (2.4 billion) have improper sanitation.
- 80% of all wastewater is discharged without treatment.
- Every day, 1000 children die of diarrheal diseases
Diseases related to contamination of drinking-water constitute a major burden on human health. Interventions to improve the quality of drinking-water provide significant benefits to health.
- World Health Organization
Point versus Nonpoint
Two types of water pollution sources:
- Point sources: pollution is from a specific location
- Examples: pipe, sewer, oil well
- Nonpoint sources: not from any single site
- Examples: agricultural runoff, oil from city streets
- Nonpoint sources are very difficult to control
Types of water pollution
- dissolved organic matter
- toxic chemicals
The source of pathogens in water is human and animal wastes. Since here we are talking about waterborne diseases, if they are found in water they must originate from the gut of either animals or humans.
Coliforms are only naturally found in the gut of animals (including humans). Therefore, we can use the concentration of coliform in water as an indicator of possible presence of pathogens. The coliform test is a very commonly used test for water pollution.
Dissolved Oxygen - Oxygen which is dissolved in the water
It is necessary for fish and other aquatic organisms to survive. Often it is the limiting factor for these species.
Dissolved Organic Matter
Dissolved Organic Matter includes manure and plant debris. Human sources include sewage, runoff from feedlots, and paper mills.
- Microorganisms (decomposers) breakdown the dissolved organic matter
- As these decomposers use oxygen, they remove dissolved oxygen from the water.
- The resulting lowered dissolved oxygen my be too low for fish to survve, causing fish kills.
The measure of the amount of oxygen-demanding wastes is the Biological Oxygen Demand (BOD). It is the amount of dissolved oxygen needed by aerobic decomposers to break down organic matter at 20 degrees Celsius in 5 days.
Ironically, nutrients - especially nitrates and phosphates - can cause water pollution.
Sources: sewage, agricultural runoff from fertilizers, detergents (these contain phosphorus).
Excess nutrients can cause a condition called eutrophication.
- Excess nutrients cause algae and other aquatic plants to grow (an algal bloom)
- When these die, decomposers feed on them deplete the dissolved oxygen
- This can kill fish and other aquatic organisms.
Fine particles can become suspended in the water column. The main source is soil erosion.
They can have a number of effects:
- reduce photosynthesis
- carry bacteria, toxic chemicals, and nutrients
- settle on the bottom covering fauna
- fill lakes and reservoirs
Water used to cool power plants and other industries is often released to rivers or lakes.
This hot water changes the water temperature. This in turn lowers dissolved oxygen and disrupts the normal activity of aquatic organisms.
It also increases evaporation.
Many chemicals are toxic: lead, arsenic, pesticides, oil, etc.
Sources: surface runoff, industrial effluents, seepage from landfills.
Toxic chemicals can cause a variety of health effects. They can also harm fish and wildlife.
Wastewater treatment is the removing of contaminatess found in wastewater. This section will focus on municpal wastewater (sewage). Note: do not confuse wastewater treatment with water treatment.
Let us look at the above components individually:
- Filter - this is to remove large pieces of debris such as bottles, wood, or metal
- Settling Tank - removes non-organic materials - for example, soil
- Aerobic Decomposition - most commonly Activated Sludge system which pumps air into the wastewater to encourage bacterial decomposers to digest the waste.
- Anaerobic Digestion - decomposes any remaining organic matter in the sludge
Some other parts may also exist:
- In place of an activated sludge system, trickling filters may be used. These slowly run water of rocks onto which bacteria to form a film.
- For small-scale uses, a septic tank - these tanks act as both a settling tank and as a place for degradation of organic waste
- Wetlands may be used after the primary treatment. This uses the natural process to treat the waste.