Waste Water Engineering

131. In septic tanks,

1. Free board of 0.3 m may be provided
2. The baffles or tees are extended up to top level of scum
3. The clear space between the baffle top and covering slab is about 7.5 cm
4. All the above

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132. In septic tanks, decomposition of organic bacteria, is done by

1. Anaerobic bacteria
2. Aerobic bacteria
3. Both types of bacterias
4. None of these

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133. In sewage having fully oxidised organic matter, the nitrogen exists in the form of

1. Nitrites
2. Nitrates
3. Free ammonia
4. Aluminoid nitrogen

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134. In sewage, the solids in mg per litre is

1. 100 to 500
2. 500 to 1000
3. 1000 to 1500
4. 1500 to 2000

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135. In sewers designed with self cleansing velocity,

1. The bottom is silted
2. The bottom is scoured
3. Both silting and scouring occur at the bottom
4. Neither silting nor scouring occurs at the bottom

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136. In sewers the effect of scouring is more on

1. Top side
2. Bottom side
3. Horizontal side
4. All sides

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137. In sewers the gas generally found, is

1. Hydrogen sulphide (H₂S)
2. Carbon dioxide (CO₂)
3. Methane (CH₃)
4. All the above

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138. In sewers the highest non-scouring velocity is achieved in

1. Glazed bricks sewers
2. Cast iron sewers
3. Cement concrete sewers
4. Stone ware sewers

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139. In sewers the velocity of flow should not be

1. More than the self-cleansing velocity
2. Less than the self-cleansing velocity
3. Less than 10 m/sec
4. More than 20 m/sec

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140. In SI units the power of sound is represented in

1. Kgs
2. Joules
3. Newtons
4. Watts

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