Water Pollution: Causes, Effects, and Remediation Techniques
Eutrophication: Causes and Impacts on Aquatic Life
Eutrophication consists of an increase in primary productivity caused by the introduction of bionutrients—inorganic and organic compounds containing nitrogen and phosphorus—primarily through agricultural and domestic discharges.
The contributions of phosphorus and nitrogen fuel the growth of plankton and algae, leading to massive blooms (algal blooms). This dense layer significantly reduces light penetration into the water column.
Phytoplankton photosynthetic activity generates an increase of oxygen on the surface, which often escapes to the atmosphere. Simultaneously, the accumulation of the remains of living organisms intensifies the action of aerobic bacteria. These bacteria consume large amounts of O₂ to oxidize the organic material, leading to severe oxygen depletion (anoxia) in deeper waters.
This depletion results in an anaerobic situation and the onset of fermentation processes in bottom sediments, severely damaging the aquatic ecosystem.
Subterranean Water Pollution and Aquifer Depletion
Subterranean water pollution often results from the overexploitation of aquifers. This occurs when water is extracted in excess of the aquifer's natural recharge capacity, causing a significant lowering of water tables.
Oil Spills (Black Tides) and Marine Organism Mortality
The effects of oil spills, often referred to as black tides, include the death of marine organisms due to:
- Sinking: Organisms lose buoyancy.
- Heat Loss: Oil impregnation alters the insulating properties of feathers and fur, leading to hypothermia.
Corrective Measures for Water Pollution
Common methods used to mitigate water pollution include:
- Booms and physical barriers
- Chemical agents (dispersants and sinking agents)
Bioremediation: An Eco-Friendly Solution
Bioremediation is currently the most efficient and environmentally friendly method. It is based on planting bacterial populations specifically designed to degrade pollutants. This technology is still actively in development.
Water Quality Metrics: BOD and COD Explained
Two key metrics are used to assess water quality:
- BOD (Biochemical Oxygen Demand)
- A measure of the amount of O₂ that microorganisms need to oxidize organic matter present in the water.
- COD (Chemical Oxygen Demand)
- A test measuring the oxidation of organic compounds by the action of chemical oxidizing agents. It is used to calculate the total amount of O₂ required for the oxidation of all compounds present in water, without the participation of living organisms.
Defining Water Hardness (Soft vs. Hard Water)
Water is classified based on mineral concentration:
- Soft Water: Has a concentration of minerals less than 50 mg/L.
- Hard Water: Has a concentration higher than 200 mg/L.
Water Purification and Wastewater Treatment Processes
Natural Water Purification
Purification is a system that occurs naturally in waters. It consists of mechanisms for the deposition of particles and chemical and biological processes that produce the degradation of organic matter, converting it into inorganic substances.
Stages of Wastewater Treatment
Wastewater treatment typically involves three main stages:
- Primary Treatment: The separation of suspended solids and floating material that were not retained earlier (e.g., screening and sedimentation).
- Secondary Treatment: Involves putting the wastewater in large tanks so that bacteria can biologically degrade the organic matter (e.g., activated sludge process).
- Tertiary Treatment: Designed to remove organic matter, nutrients (like nitrogen and phosphorus), and pathogens not removed in the earlier stages.