Q. No.| 1. | It basically involves the physical removal of particles – large and small. |
| 2. | Floating debris is removed by sequential filtration. |
| 3. | Grit [soli and small pebbles] are removed by sedimentation. |
| 4. | All solids that settle form the activated sludge. |
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Which one of the following impurities is easiest to remove from wastewater?
| 1. | Bacteria | 2. | Colloids |
| 3. | Dissolved solids | 4. | Suspended solids |
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The primary objective of the secondary treatment of sewage water is:
| 1. | the removal of coarse solids and other large materials often found in raw wastewater. |
| 2. | the removal of settleable organic and inorganic solids by sedimentation, and the removal of materials that will float by skimming. |
| 3. | production of biogas that can be used as an efficient fuel, especially in rural households. |
| 4. | the removal of biodegradable dissolved and colloidal organic matter using aerobic biological treatment processes. |
During which stage of the sewage treatment are the microbes used?
| 1. | Primary | 2. | Secondary |
| 3. | Tertiary | 4. | Quaternary |
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In the secondary treatment or biological treatment of sewage water, the primary effluent is passed into large aeration tanks where it is constantly agitated mechanically and the air is pumped into it. This allows:
1. vigorous growth of useful aerobic microbes into flocs
2. the decrease in the number of aerobes in the water
3. rapid increase in the count of methanogens
4. a dramatic decrease in the anaerobic methanogens
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Consider the given two statements:
| I: | BOD is an indirect measure of the organic matter present in the water. |
| II: | The BOD test measures the rate of uptake of oxygen by microorganisms in a sample of water. |
| 1. | Both I and II are correct and II explains I. |
| 2. | Both I and II are correct but II does not explain I. |
| 3. | Only II is correct. |
| 4. | Both I and II are incorrect. |
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During the secondary or biological treatment of sewage water:
| I. | The BOD of the wastewater gets reduced significantly. |
| II. | The activated sludge contains aerobic micro-organisms that can clump together. |
| III. | The entire activated sludge is pumped into anaerobic sludge digesters. |
1. Only I is correct
2. Only I and II are correct
3. I, II and III are correct
4. I, II and III are incorrect
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Given below are the results of three water samples subjected to BOD test:
| I. | Sample A can be from secondary effluent discharged from an STP. |
| II. | Sample B can be from a river presumed to be mild to moderately polluted. |
| III. | Sample C can be from untreated sewage water. |
1. Only I and II are correct
2. Only I and III are correct
3. Only II and III are correct
4. I, II and III are correct
What would happen if oxygen availability to activated sludge flocs is reduced?
| 1. | It will slow down the rate of degradation of organic matter. |
| 2. | The center of flocs will become anoxic, which would cause the death of bacteria and eventually breakage of flocs. |
| 3. | Flocs would increase in size as anaerobic bacteria would grow around flocs. |
| 4. | Protozoa would grow in large numbers. |
In the anaerobic sludge digesters during sewage water treatment:
| 1. | The primary sludge is treated with aerobic microbes and activated sludge is created |
| 2. | The primary sludge is treated with anaerobic microbes and activated sludge is created |
| 3. | The activated sludge is digested by anaerobic microbes producing biogas during the process |
| 4. | The activated sludge is digested by aerobic microbes producing biogas during the process |
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