LECTURE 4 - WENGR 4250
Introduction
Wastewater Discharge: Release of water contaminated with pollutants into freshwater systems.
Pollutants include organic matter, nutrients (primarily phosphorus and nitrogen), heavy metals, chemicals, and pathogens.
Sources: Domestic sewage, industrial processes, agricultural runoff.
Impacts of Wastewater Discharge on Water Bodies
Nutrient Overloading and Eutrophication
Excessive nitrogen and phosphorus act as fertilizers in freshwater systems.
Results in algal blooms which deplete dissolved oxygen through decomposition, leading to oxygen-deprived conditions, harming aquatic life (especially fish).
Eutrophication: Structural change in ecosystems caused by excess nutrients, leading to algal blooms and poor water quality.
Contamination of Water Quality
Introduction of heavy metals, toxic chemicals, pharmaceuticals, micro-plastics, and pathogens into water bodies.
Compromises water quality, making it unsafe for human consumption, irrigation, and recreation.
Accumulation of contaminants in aquatic organisms poses risks to human health via the food chain.
Destruction of Aquatic Ecosystems
Disruption of the balance in freshwater ecosystems.
Toxic substances and reduced oxygen harm aquatic organisms, leading to biodiversity loss.
Impact on habitats like wetlands, which provide essential ecological services.
Harm to Human Health
Untreated wastewater contains pathogens like bacteria, viruses, and parasites.
Can cause waterborne diseases (cholera, dysentery, hepatitis).
Communities relying on contaminated freshwater are at risk of illness.
Pollution by Organic Matter & Stream Self-Purification
Self-Purification: Natural reestablishment of ecological balance after effluent discharge.
Pollution Characterization: Species diversity indicates presence or absence of pollution.
Self-Purification Zones
Degradation Zone: Begins immediately after wastewater discharge; water is turbid and rich in organic solids.
Active Decomposition Zone: Microorganisms proliferate; oxygen levels drop.
Recovery Zone: Water begins to clear; microbial activity reduces.
Clean Water Zone: Water returns to quality similar to pre-pollution state.
Characteristics of Zones
Degradation Zone: Turbid water, increased carbon dioxide, anaerobic conditions prevail in sludge.
Active Decomposition Zone: High levels of nitrogen; ammonia conversion starts.
Recovery Zone: Increasing biodiversity and clearer water; stable ecosystem begins to form.
Clean Water Zone: Similar to pre-pollution conditions; stable aquatic community achieved.
Contamination by Pathogenic Microorganisms
Sewage discharged into water bodies incorporates pathogenic organisms affecting human uses like potable water supply, irrigation, and bathing.
Eutrophication of Lakes and Reservoirs
Eutrophication: Excessive growth of aquatic plants due to high nutrient levels, primarily nitrogen and phosphorus.
Development of Eutrophication Process:
Land Occupation by Woods and Forests: Natural vegetation leads to low productivity.
Agricultural Use: Intermediate stage of water body deterioration through nutrient runoff.
Urban Occupation: Faster deterioration due to urban drainage and stormwater.
Sewage: Contains nitrogen and phosphorus, further contributing to nutrient loading.
Quality Standards for Wastewater Discharges and Water Bodies
National Standards: Legally defined based on specific conditions of each country.
Regional Standards: Developed for specific political divisions, often more stringent than national standards.
Guidelines: Proposed by entities like WHO, aimed at protecting public health and the environment.
Types of Standards
Discharge Standards: Regulation of effluent emissions.
Water Quality Standards: Standards for receiving water bodies.
Standards or quality guidelines: Quality standards for treated effluent use, e.g., irrigation.