Question

Secondary sludge uses?
A) gravitational sedimentation
B) primary clarifier
C) non-biodegradable materials
D) micro-organisms to consume waste organic

Answer 1

Hint: In sewage treatment plants(STPs) sewage is given treatment to make it polluting to a lesser degree.By the use of different microbes naturally present in the sewage , Treatment of waste water is done . This treatment is carried out in two stages: Primary and secondary.

Complete step-by-step answer:
Primary treatment involves the physical removal of particles from the sewage through filtration and sedimentation. All the solid simmer down from the primary sludge and the floating part forms the effluent. The discharge from the primary settling tank is taken in secondary treatment.
Secondary treatment is also called biological treatment in this system primary effluent is passed into an aerator where it is constantly flustered mechanically and the air is pumped into it. This allows healthy growth of useful microbes which cannot survive in the absence of air into flocs(masses of bacteria associated with the fungal part).
Once the BOD of sewage or waste is decreased significantly, the discharge is then passed into a sedimentation tank where the bacterial flocs are allowed to sediment. This deposit is called activated sludge. Activated sludge is also called secondary sludge. The activated waste biomass resulting from biological treatments is called secondary sludge. Some activated sludge is put back into the aeration tank to serve as inoculum. The leftover part of the sludge is forced into a large tank called anaerobic sludge digesters. Here, other kinds of bacteria, which grow anaerobically that do not need oxygen, digest the bacteria and fungi in the sludge. During this maceration, bacteria generate a combination of gasses such as methane, hydrogen sulphide, and carbon dioxide. These gasses form marsh gas and can be used as a source of energy as it is combustible.
Hence the correct answer is option (D).





Note: The effluent from the secondary treatment plant is generally released into natural water bodies like rivers and streams. But sewage is produced in larger quantities and there are not enough sewage treatment plants so our rivers are getting polluted.