With respect to particle settling in wastewater treatment systems; the correct statement(s) is/are
- Settling in grit chamber and primary sedimentation tanks are examples of Type-I settling
- Settling in primary sedimentation tank and secondary sedimentation tank are examples of Type-II settling
- Settling in grit chamber is an example of Type-I settling, whereas settling in primary sedimentation tank is an example of Type-II settling
- Settling in secondary sedimentation tank is an example of Type-III settling, whereas settling in primary sedimentation tank is an example of Type-II settling
The Correct Option is C, D
Solution and Explanation
Step 1: Define settling types in wastewater treatment.
Type-I settling (Discrete settling): Occurs when particles settle independently without interaction. Common in grit chambers.
Type-II settling (Flocculent settling): Occurs when particles flocculate and settle as groups. Seen in primary sedimentation tanks.
Type-III settling (Hindered settling): Occurs when particles settle as a layer due to high concentrations. Found in secondary sedimentation tanks.
Type-IV settling (Compression settling): Occurs when particles settle under the influence of compression at very high concentrations.
Step 2: Analyze the options.
(1) Settling in grit chamber and primary sedimentation tanks are examples of Type-I settling: Incorrect. Grit chambers involve Type-I settling, but primary sedimentation involves Type-II settling.
(2) Settling in primary sedimentation tank and secondary sedimentation tank are examples of Type-II settling: Incorrect. Secondary sedimentation involves Type-III settling, not Type-II.
(3) Settling in grit chamber is an example of Type-I settling, whereas settling in primary sedimentation tank is an example of Type-II settling: Correct. (
4) Settling in secondary sedimentation tank is an example of Type-III settling, whereas settling in primary sedimentation tank is an example of Type-II settling: Correct.
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