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