By
Dr Emmanuel Odjadjare
POLLUTION AND SELF PURIFICATION
Water Pollution Pollution is the introduction of materials and/or
effects at harmful level
Pollution could be natural or man made
Water pollution is any modification that directly or indirectly, changes the quality of water and disturbs or destroys the balance of ecosystems and natural resources, so that it:
causes hazards to public health,
detracts from the convenience, efficiency and well-being of man and his communities and
impairs the beneficial uses of water.
Effects of Pollution Physiological damage to man and useful organisms
Transmission and release of pathogenic microbes
Reduction of the oxygen resources of water bodies
Eutrophication
Damage to food chains caused by the accumulation
of poisonous substances in living organisms.
Impairment or destruction of aesthetic values
Sources of Water Pollution Point Sources
domestic and industrial wastes discharges wastes from specific drain pipes, ditches,
sewer lines
Nonpoint sources
atmospheric deposition, agricultural / industrial / residential runoff
MAJOR TYPES OF POLLUTANTS
Petroleum Products
Herbicides and Pesticides
Infectious Agents e.g. Bacteira, fungi, viruses, parasites
Giardia lamblia
Other Pollutants Heavy metals e.g. copper, lead, mercury, and
selenium,
Harzardous wastes e.g. poisonous, explosive, and inflamable chemicals, substances or radiations
Excess organic matter e.g. sewage effluent,
Sediment
Pollution of Freshwater stream
Flowing streams can recover from a moderate level of degradable water pollutants if they are not overloaded and their flows are not reduced
In a flowing stream, the breakdown of degradable wastes by bacteria depletes DO and creates an oxygen sag curve
This reduces or eliminates populations of organisms with high oxygen requirements.
Pollution of Freshwater Lakes Dilution of pollutants in lakes is less effective
than in most streams
Lakes and reservoirs are often stratified and undergo little mixing
Low flow makes them susceptible to runoff
Various human activities can overload lakes with plant nutrients, which decrease DO and kill some aquatic species.
Pollution of Groundwater Groundwater can become contaminated with a variety of
chemicals
it cannot effectively cleanse itself, dilute and disperse pollutants
It can take hundreds to thousands of years for contaminated groundwater to cleanse itself of degradable wastes.
Nondegradable wastes (toxic lead, arsenic, flouride) remain there permanently
Ocean Pollution
SELF PURIFICATION OF NATURAL WATERS
Introduction Self-purification describes the ability of natural
water bodies to gradually clean themselves, and improve the quality of water over time
The water is ‘purified’ in the sense that the concentration of waste material has been reduced drastically
Self purification ensures stability of the aquatic ecosystem in the interest of all members of the community
Actions Involved in Self purification Dilution
Dispersion due to Currents Prevents local accumulation of pollutantsAids mixing and reaeration
Sedimentation
TemperatureDissolution of chemicalsSedimentation effects Improved microbial activity Solubility of DO
Sunlight Increased DO through photosynthesis
UV irradiation reduces microbial population
Biological Action through:Organic matter degradation
Two groups are mainly involved: Plankton
Benthos
ZONES OF POLLUTION IN WATER (STREAM)