Question

Which of the following is correct for sewage discharge in a river?
A. At the discharge point, B.O.D is high and fishes die
B. At the discharge point, D.O is high
C. B.O.D increases downstream in the river
D. From the discharge 50 KM away, fishes die

Answer 1

Hint: Sewage is a type of wastewater that is produced by humans. Sewage is a complex mixture of chemicals that has many chemical characters. They are characterized by a physical condition, chemical and toxic constituents, and bacteria status.

Complete answer:
It consists of water from sinks, bathtubs, showers, dishwashers, and clothes washers called greywater. Blackwater is used to flush toilets combined with human waste, and detergents, soaps, etc. The wastewater produced remains untreated, which causes water pollution and the waste present here is released into the environment which is untreated. The organic matter of sewage is decided on the basis of B.O.D (biological oxygen demand) or C.O.D (chemical oxygen demand). Biological oxygen demands the amount of oxygen consumed by bacteria and microorganisms under specified conditions and temperature and microorganisms decompose organic matter under the presence of oxygen (aerobic). The greater the BOD, the greater the amount of oxygen in the stream, which means less oxygen available to aquatic life. If high BOD, the aquatic organisms become stressed, suffocate, and die. At the discharge point, B.O.D is high and fishes die when the sewage is released into the river. The BOD is the same as for low dissolved oxygen (DO). Low BOD is an indicator of good quality of water and high BOD indicates polluted water.

Hence, the correct answer is Option A

Note: Sewage or domestic wastewater or municipal wastewater. It includes high pH, high conductivity, high alkalinity. Sewage treatment includes the removal of contaminants from sewage and makes them useful for the environment or reuse.