Select the correct statements regarding dissolved oxygen and Biochemical Oxygen Demand. [2023]
(A) BOD is inversely related to dissolved oxygen.
(B) Low dissolved oxygen and high BOD lead to loss of aquatic life.
(C) High BOD leads to high dissolved oxygen.
(D) Both BOD and dissolved oxygen are indicators of health of a water body.
(E) Both BOD and dissolved oxygen are affected by amount of organic matter in the water body.
Choose the most appropriate answer from the options given below.
(A), (B), (C), (E) only
(A), (B), (D), (E) only
(A), (B), (C), (D) only
(B), (C), (D), (E) only
(2)
High BOD means high amount of organic matter in water. The more the BOD, the lesser will be the dissolved oxygen, as it gets used up.
Which of the following is put into anaerobic sludge digester for further sewage treatment? [2020]
Primary sludge
Floating debris
Effluents of primary treatment
Activated sludge
(4)
The sediment in a settling tank is called activated sludge. A small part of it is pumped back into the aeration tank to serve as the inoculum. While the remaining major part of the sludge is pumped into large tanks called anaerobic sludge digesters.
Which of the following in sewage treatment removes suspended solids? [2017]
Secondary treatment
Primary treatment
Sludge treatment
Tertiary treatment
(2)
Primary or physical treatment is the process of removal of small and large, floating and suspended solids from sewage through two processes of filtration and sedimentation.
What gases are produced in anaerobic sludge digesters? [2014]
Methane and only
Methane, Hydrogen sulphide and
Methane, Hydrogen sulphide and
Hydrogen sulphide and
(2)
The type of gases produced by microbial activity depend upon the microbes and the organic substrates they utilise. Certain bacteria, called methanogens, grow anaerobically on cellulosic material and produce large amount of methane along with carbon dioxide. These bacteria are commonly found in the anaerobic sludge during sewage treatment. Other anaerobic bacteria, involved in the process of anaerobic digestion produce other gases like ammonia and hydrogen sulphide.
