MPSC State Service 2020 · CSAT · Question 31 of 77

Passage: Read the following passage and answer the questions from. When sewage is dropped on land, the bacteria present in the soil attack on it and convert the content of sewage into plant food. The latter gets utilized by the roots of the plants or crops. The organic matter present in sewage undergoes decomposition by aerobic and non-aerobic bacteria, but it is profitable to provide aerobic conditions for the disposal of sewage by land treatment. The oxygen that is required for aerobic decomposition, is present in different layers of the soil. The CO2 produced as a result of decomposition is given by the soils and in turn, atmospheric oxygen is absorbed. This interchange of oxygen and carbon dioxide take place by wind movements, difference is temperature and pressure, drainage of soils and many other processes. When sewage is applied on land, the chemical process of oxidation takes place in which organic matter of the sewage is oxidised by bacteria. Filtration is the principal physical action that is involved in the purification of sewage by land treatment. Sewage as it passes through the layers of the soils gives out suspended particles which are retained by the voids of the soil. In presence of sufficient aeration, these particles are oxidised by aerobic bacteria. This physical action mainly depends on the nature of the soil. Most suitable and satisfactory filtration takes place in porous, loamy or sandy soils. The heavy soils such as clay are not very suitable for filtration, while rocky soils are most unsuitable for filtration. The major portion present in sewage is water, and it can be used for irrigation. Sewage also contains nitrogen, potash, phosphate, organic acids etc and so it has a good fertilizer value, because these constituents present in sewage can be directly used by the plants for their growth. In this way, sewage increases the fertility of the soils and also improves the condition of the soil. The type of crop that can be grown, mainly depends on the quality of sewage and health regulations concerning the use of sewage on crops. During the aerobic decomposition of sewage, by bacteria ________. a. the required oxygen is directly taken from the atmosphere b. the produced carbon dioxide is interchanged with the atmospheric oxygen c. the carbon dioxide present in different layers of soil is used

Reading Comprehension

1. Aa and b
2. BbCorrect
3. Cb and c
4. DNone of the above