Question 4 With respect to the type of processes taking place, what is the diffe

Question

Question 4 With respect to the type of processes taking place, what is the difference between primary and secondary sedimentation in wastewater treatment? 111) They are the same, the solids in both are composed mainly of biological "flock" grown in the activated sludge tank or other biological process preceding the sedimentation basin. O Both (II) and (II). 1) There is very little difference between the two in terms of process. The primary difference is the type of solids being "Settled" 11) They are the same, the solids in both are from raw wastewater and tend to be composed of a variety of inorganic and organic materials. Dll F8 F4 F5 F6 F7

Explanation / Answer

Primary clarifier or Primary sedimentation tank is mainly used to remove the settelable organic solids and suspended solids present in the waste water through gravitational sedimentation. In this process, water is stored at rest for sometime and sludge collected at the bottom and oily matter collected at the top are removed. Main suspended solids of settelable organic solids(biodegradable) of 60 to 70% and 20 to 30% BOD removal takes place here. Primary sedimentation tank follows the Type III or Hindered settling in which the particles are closely spaced and concentration is more.

Secondary Sedimentation Tank or secondary clarifier settle the biological flocs(microorganisms) from the waster water flow. The suspended particles containing the microbes in the wastewater are removed which entered the tank after the activated sludge process. The process uses the microogranisms to consume the organic matter in the wastewater. It follows the Type-IV settling also known as the compression settling or zone settling.

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