The correct answer is D. All the above.
Dissolved oxygen (DO) is the amount of oxygen that is dissolved in water. It is essential for aquatic life, as it is used in respiration. The amount of DO that can be dissolved in water depends on the temperature and salinity of the water. In treated sewage, 4 ppm of DO is essential to support aquatic life. Only very fresh sewage contains some DO, as it is quickly used up by bacteria. The solubility of oxygen in sewage is 95% that is in distilled water.
Here is a more detailed explanation of each option:
- Option A: In treated sewage, 4 ppm of D.O. is essential.
DO is essential for aquatic life, as it is used in respiration. The amount of DO that can be dissolved in water depends on the temperature and salinity of the water. In treated sewage, 4 ppm of DO is essential to support aquatic life.
- Option B: Only very fresh sewage contains some dissolved oxygen.
Sewage is a mixture of human waste, wastewater, and industrial waste. It is a complex mixture of organic and inorganic matter. The amount of DO in sewage is quickly used up by bacteria. Only very fresh sewage contains some DO.
- Option C: The solubility of oxygen in sewage is 95% that is in distilled water.
The solubility of oxygen in water is affected by temperature and salinity. The solubility of oxygen in water decreases as the temperature increases. The solubility of oxygen in water also decreases as the salinity increases. The solubility of oxygen in sewage is 95% that is in distilled water.
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