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Environmental (101-120)

Updated: Apr 26, 2020

101. Most suitable section of sewer in separate sewage system is circular section


102. An egg shaped section of sewer provides self cleansing velocity at

low discharges


103. The velocity of flow does not depend on length of sewer


104. The hydraulic!mean depth (HMD) for an egg-shaped sewer flowing two-third full is greater than HMD when flowing full


105. The effect of increasing diameter of sewer on the self cleansing velocity is

to increase it


106. The most commonly used sewer under culverts is circular brick sewer


107. The type of sewer which is suitable for both combined and separate system is

egg shaped sewer


108. The characteristics of fresh and septic sewage respectively are alkaline and acidic


109. The pathogens can be killed by chlorination


110. Which of the following retards the self purification of stream ? none


111. Sewage treatment units are normally designed for 15-20 years


112. Settling velocity increases With depth of tank


113. Standard BOD is measured at 20°C - 5 day


114. The correct relation between theoretical oxygen demand (TOD), Biochemical

oxygen demand (BOD) and Chemical oxygen demand (COD) is given by



115. 5 day BOD is less than 4 day BOD keeping other conditions same


116. If Biochemical oxygen demand (BOD) of a town is 20000 kg/day and BOD per

capita per day is 0.05 kg, then population equivalent of town is 400000


117. The rate of BOD exerted at any time is directly proportional to BOD remaining


118. The ratio of 5 day BOD to ultimate BOD is about 2/3


119. In a BOD test, 1.0 ml of raw sewage was diluted to 100 ml and the dissolved

oxygen concentration of diluted sample at the beginning was 6 ppm and it was 4 ppm at the end of 5 day incubation at 20°C. The BOD of raw sewage will be

200 ppm


120. The minimum dissolved oxygen which should always be present in water in order to save the aquatic life is 4 ppm

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