Eutrophication

• Eutrophication derives from the Greek word eutrophos, meaning nourished or enriched.
• Eutrophication escalates rapidly when high nutrients from fertilizers, domestic and industrial wastes, urban drainage, detergents and animal, sediments enter water streams.
• Eutrophication is mainly divided into natural and cultural Eutrophication. In natural Eutrophication, a lake is characterized by nutrient enrichment. During this process an oligotrophic lake is converted into an eutrophic lake. It permits the production of phytoplankton, algal blooms and aquatic vegetation that in turn provide ample food for herbivorous zooplankton and fish.
• Cultural Eutrophication is caused by human activities. Which in turn are responsible for addition of 80% nitrogen and 75% phosphorus to lake and streams.
• Eutrophication causes several physical, chemical and biological changes, which considerably deteriorate the water quality.
• It creates algal bloom, releases toxic chemicals that kill fish, birds and other aquatic animals.
• Decomposition of algal bloom leads to the depletion of oxygen in water. Thus with a high CO₂ level and poor oxygen through reduction of nitrates.
• On complete exhaustion of nitrate, oxygen may as last resort be obtained by reduction of sulphate yielding hydrogen sulphide causing foul smell and putrefied taste of water. Many pathogenic microbes, viruses, protozoa and bacteria and grow on sewage products under anaerobic conditions. It results into the spread of fatal water-borne disease such as polio, dysentery, diarrhoea, typhoid and viral hepatitis.

Control of Eutrophication

• Several prevention and technical devices have been used to control Eutrophication. The wastewater must be treated before its discharge into water streams.
• Recycling of nutrients can be checked through harvest. Removing nitrogen and phosphorous at the source, division of nutrient-rich waters from the receiving bodies and dilution of these elements can minimize Eutrophication.
• Algal blood should be removed upon their death and decomposition. Limiting the dissolve nutrients can control algal growth. The most suitable, feasible and effective method involves the use of chemicals to precipitate additional phosphorus.
• Precipitants like alum, lime, iron and sodium aluminate may be used. Physicochemical methods can be adopted to remove nutrients. for example phosphorous can be removed by precipitation and nitrogen by nitrification or denitrification.
• Electrodialysis, reverse osmosis and ion exchange methods. Cooper-sulphate and sodium arsenite are employed for killing algae and rooted planet respectively.