Aquatic Pollution and Coastal Management

Unit 1 : Classification of aquatic pollution

1.9.1.Physical Pollution of Water

Colour
Colour change is not harmful unless it is associated with a toxic chemical but it may affect the quality of sunlight that penetrates to a given depth inhibiting plant and animal metabolism.
Most of the trade wastes discharged into water systems have pronounced colours due to organic dyes and inorganic complexes. It has been reported that even a micro quantity (0.02 ppm) of magenta in water imparts a distinct red colouration. Tannery wastes when discharged into iron containing water streams form deep green or blue colouration because of the interaction of tannins with iron. Water also becomes intensely coloured due to the interaction between naturally occurring components in water and trade effluents which make it unsuitable for various purposes.

Turbidity
Turbidity in water mainly arises from colloidal matter, fine suspended particles and soil erosion. Generally greater the turbidity, stronger is the sewage and the industrial effluent concentrations and worst are the effects. Hence the degree of turbidity of a water course may be taken as a measure of the intensity of pollution. However, non-turbidity does not mean that water is unpolluted, because clear water may also be heavily contaminated with acids, alkalies, etc., which do not cause turbidity.

Turbid water becomes unsuitable for industrial purposes and also for domestic use because Fe, Mn, Ni, Co, Pb, Sb, Bi, present in it may cause stains on clothes, sinks and baths.

Measurements are useful in the evaluation of the effects of pollution by wastewaters and to follow the course of self-purification of rivers,streams . Colloidal particles, i.e., clay in natural waters and carbohydrates, proteins, and fats in waste waters can be stabilized by adding certain ions. Various coagulants like ferric chloride, ferric sulphate and ferric alum can check the turbidity of water.

Taste
Unpleasant earthy or musty taste and odour are produced by industrial effluents containing Fe, Mn, free chorine, phenols and aquatic actinomycetes. For example, even 0.1 ppm of Fe can produce an inky taste, while phenol produces a bitter taste at 7 ppm. Mn, oils, hydrocarbons, chlorophenols, petroleum products, synthetic detergents, pesticides, etc produce characteristic tastes in water. The decomposed organic matter, algae, fungi, bacteria and pathogens impart peculiar taste. However, these pollutants can be removed by conventional water purification techniques like chlorination, chemical precipitation and using activated carbon.

Odour
Odour pollution of water is caused both by chemical agents (like hydrogen sulphide, free chlorine, ammonia, phenols, alcohols, esters, hydrocarbons) and biological agents (such as algae, fungi, microorganisms). The lower the pH, the higher will be the amount of H2S produced and greater will be the odour nuisance. Certain organic and inorganic compounds of nitrogen, sulphur, phosphorus and putrefied organic matter present in sewage cause foul odour in polluted water.
Microorganisms like algae, Oscillatoria and Rivularia cause muddy odour, while Anabaena produces a strong grassy odour. A protozoa (Dinobryon) imparts fishy odour to water. According to Fair and Whipple, the liberation of essential oils is the main cause of odour pollution.

Recently, the Royal Commission on Sewage Disposal (London) identified the odour from polluted water as follows:

• Fishy odour due to organic amines
• Wormy smell probably due to phosphorus compounds
• Rotten egg or putrid smell due to HS
• Earthy odour due to humus

Foam
Foam is produced by soaps, synthetic detergents and untreated organic effluents from paper and pulp industries.