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Environmental (121-140)

Updated: Apr 26, 2020

121. The relative stability of a sewage sample, whose dissolved oxygen is same as the total oxygen required to satisfy BOD, is 100


122. Dissolved oxygen in streams is maximum at noon


123. Facultative bacteria are able to work in presence as well as in absence of



124. The means of access for inspection and cleaning of sewer line is known as



125. Sewerage system is designed for maximum and minimum flow


126. Sewage treatment units are designed for average flow only


127. Laying of sewers is usually done with the help of sight rails and boning rods


128. Corrosion in concrete sewers is caused by septic conditions


129. If the sewage contains grease and fatty oils, these are removed in skimming tanks


130. Generally the detention period for grit chambers is kept as 1 minute


131. Which of the following unit works in anaerobic conditions'? sludge digestion tank


132. Septic tank is a i) settling tank ii) digestion tank


133. The maximum efficiency of BOD removal is achieved in oxidation ditch


134. The working conditions in imhoff tanks are anaerobic in lower compartment and aerobic in upper compartment


135. In facultative stabilization pond, the sewage is treated by dual action of aerobic bacteria and anaerobic bacteria


136. The detention period for oxidation ponds is usually kept as 10 to 15 days


137. Composting and lagooning are the methods of sludge disposal


138. The main disadvantage of oxidation pond is that large area is required for construction


139. For satisfactory working of a sludge digestion unit, the pH range of digested

sludge should be maintained as 6.5 to 8.0


140. Sludge volume index is defined as the ratio of percentage of sludge by volume to percentage of suspended solids by weight

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