Water Quality and Pollution

Biological treatment of the waste water can be performed with the use of microbes. The bacteria and fungal cells are commonly used in the treatment of the water through activated sludge. Activated sludge refers to floc of microorganisms including bacterial cells and fungal filaments which are used in the process to break down organic matter into carbon dioxide, water, and other inorganic compounds and help in the clearing of the water. 

Eichhornia crassipes, commonly known as common water hyacinth, is an aquatic plant native to the Amazon basin, and is often a highly problematic invasive species outside its native range. Water hyacinth is a free-floating perennial aquatic plant (or hydrophyte) native to tropical and subtropical South America. With broad, thick, glossy, ovate leaves, water hyacinth may rise above the surface of the water as much as 1 meter in height. One of the fastest growing plants known, water hyacinth reproduces primarily by way of runners or stolons, which eventually form daughter plants. Each plant additionally can produce thousands of seeds each year, and these seeds can remain viable for more than 28 years. It was introduced in Bengal in India because of its beautiful flowers and shapes of leaves, but turned out to be an invasive weed draining oxygen from the water bodies and resulted in death of many fish. Fish is a supplement food in Bengal, and because of the fish scarcity in Bengal caused by Eichhornia, the water hyacinth is also called "Terror of Bengal".

BOD is a chemical procedure for determining the amount of dissolved $O _2$, needed by aerobic biological organisms in a body of water to break down organic material present in a given water sample at a certain temperature over a specific time period.

A bioindicator is a living organism that gives us an idea of the health of an ecosystem. Some organisms are very sensitive to pollution in their environment, so if pollutants are present, the organism may change its behaviour, or it could even die. Sewage fungus is a thick growth of fungi that develops on stagnant water contaminated with sewage effluents. The filamentous fungus indicates that the sewage has not had secondary treatment. Adult stoneflies are always found near freshwater only as aquatic larvae. As water temperature increases, the larvae dies. As BOD increases in polluted water, there occurs an increase in haemoglobin possessing blood and sludge worms. Hence, the correct answer is option E.

Hydroponics is the technique of growing plants using a water-based nutrient solution rather than soil. Minerals and nutrients are supplied directly to the plant roots in an aqueous medium.

Eutrophication, the excessive growth of algae, is primarily caused by the influx of inorganic nutrients like nitrates and phosphates into water bodies.

Bioremediation is the use of microorganisms (like bacteria or fungi) to consume and break down environmental pollutants, such as oil spills, into less toxic substances.

Pollution renders existing water unusable, population growth increases demand, and industrial development consumes large quantities of water, all contributing to scarcity.

The water cycle (hydrologic cycle) is the continuous movement of water on, above, and below the surface of the Earth, which naturally purifies and replenishes water bodies.

Dissolved oxygen means the  free or  non-compound oxygen present in water or in  other liquids. Dissolved oxygen is important to many forms of life including fish, bacteria and plants. These organisms use oxygen in respiration, similar to organisms on land. Fishes obtain oxygen for respiration through their gills, while plant life and phytoplankton require dissolved oxygen for respiration when there is no light for photosynthesis.

So the given statement If dissolved oxygen is not present, the aquatic life would die.

1. Arsenic poisoning causes black foot disease as arsenic is a carcinogen that results in darkening of the skin and abdominal issues.
   2. Secondary treatment to the effluents involves a biological process in which the organic matter in the effluent is decomposed by the bacteria and fungi.
   3. Pyrolysis is the process in which the solid soil is subjected to the high temperature to decompose it into ash.
   4. Tubifex is a roundworm that can sustain the polluted water that has low levels of dissolved oxygen and heavy metal deposition. So, its growth in any water body indicates water pollution.
   5. Biomagnification is the ability of the non-degradable pollutants to stay in the adipose tissues of the living organisms and persist in higher concentration.
   Hence, the correct answer is '1,2,3,4'.

Biochemical oxygen demand (BOD) is a measure of how much organic pollution is in water. The BOD test measures the amount of dissolved oxygen in water that is used up due to the breakdown of organic pollutants, such as sewage, in a certain number of days.

Untreated sewage is an excellent source of bacterial growth. Such untreated sewage can result in spread of many bacterial diseases like outbreak of epidemics, cholera, typhoid etc.

Dissolved salts in water are important because
(A) They provide taste
(B) Growth of plants
(C) Minerals essential for body
Water contains dissolved salts which provide taste to water for drinking purposes. Also these salts are essential for growth and development of plants. These dissolved salts provide the essential minerals which are required for growth of body.