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)