. Eutrophication When run-off from land containing nutrients reaches water bodies like lakes, it results in dense growth of plant life. This phenomenon is called Eutrophication . Natural aging of lakes also leads to nutrient enrichment of its water.
In a lake, the water is cold and clear ( oligotrophic stage ), supporting little life. With time, streams draining into the lake introduce nutrients such as nitrates and phosphates, which encourage the growth of aquatic organisms. Aquatic plants and animal life grow rapidly, and organic remains begin to be deposited on the lake bottom ( mesotrophic stage ) (Fig. .
). Pollutants from anthropogenic activities like effluents from the industries and homes Fig. . Stages of Eutrophication XII Std Biology-Zoology Chapter- XII Std Biology-Zoology Chapter- Environmental Issues greater the BOD of the waste water more is its polluting potential.
Once the BOD of sewage water is reduced significantly, the effluent is then passed into a settling tank where the bacterial “flocs” are allowed to sediment. This sediment is called activated sludge. A small part of activated sludge is pumped back into the aeration tank to serve as the inoculum. The remaining major part of the sludge is pumped into large tanks called anaerobic sludge digesters.
Here, the bacteria which grow anaerobically, digest the bacteria and the fungi in the sludge. During this digestion, bacteria produce a mixture of gases such as methane, hydrogen sulphide and CO . These gases form biogas and can be used as a source of energy. Tertiary treatment Tertiary treatment is the final process that improves the quality of the waste water before it is reused, recycled or released into natural water bodies.
This treatment removes the remaining inorganic compounds and substances, such as nitrogen and phosphorus. UV is an ideal disinfectant for wastewater since it does not alter the water quality – except for inactivating microorganisms. UV is a chemical- free process that can completely replace the existing chlorination system and also Primary treatment Primary treatment involves the physical removal of solid and particulate organic and