Environmental Engg. Notes for GATE, PSUs preparations - part 6

Hello There,

How have you been? Here is the 6th part of your preparatory content, useful for GATE and PSUs.

• Most suitable section of sewer in separate sewage system is circular section.
• An egg shaped section of sewer provides self cleansing velocity at low discharges.
• The velocity of flow in sewer depends upon grade of sewer, hydraulic mean depth of sewer and roughness of sewer but not upon length of sewer.
• The hydraulic mean depth(HMD) for an egg-shaped sewer flowing two-third full is greater than HMD when flowing full.
• The effect of increasing the diameter of sewer on the self cleansing velocity is to increase it.
• The most commonly used sewer under culverts is circular brick sewer.
• The type of sewer which is suitable for both combined and separate system is egg shaped sewer.
• The characteristics of fresh and septic sewage respectively are alkaline and acidic.
• The pathogens can be killed by chlorination.
• Sewage treatment units are normally designed for 15-20 years.
• Settling velocity increases with depth of tank.
• Standard BOD is measured at 20 degrees Celcius - 5 day.
• The correct relation between Theoretical oxygen demand(TOD), Biochemical Oxygen Demand(BOD) and Chemical Oxygen Demand(COD) is TOD>COD>BOD.

Thanks for visit!

Reference: Book " Civil Engineering Objectives" by S P Gupta and S P Gupta.