Friday, January 3, 2014

Environmental Engg. Notes for GATE, PSUs preparations - part 8

Hello there,

Welcome to the part 8 of the one liner notes useful for the preparation of GATE and other similar examinations.

  • Sewage treatment units are designed for maximum flow.
  • Laying of sewers is usually done with the help of sight rails and boning rods.
  • Corrosion in concrete sewers is caused by septic conditions.
  • If the sewage contains grease and fatty oils, these are removed in skimming tanks.
  • Generally the detention period for grit chambers is kept as 1 minute.
  • Sedimentation tank units run in anaerobic conditions.
  • Septic tank is an aeration tank.
  • The maximum efficiency of BOD removal is achieved in trickling filters.
  • The working conditions in imhoff tanks are aerobic in lower compartment and anaerobic in upper compartment.
  • In facultative stabilization pond, the sewage is treated by sedimentation.
  • The detention period for oxidation ponds is usually kept as 4-8 hours.
  • Composting and lagooning are the methods of sludge disposal.
  • The main disadvantage of oxidation pond is that BOD removal is very low.
  • For satisfactory working of a sludge digestion unit, the pH range of digested sludge should be maintained as 8.5 to 10.0.
  • Sludge volume is defined as the ratio of percentage of suspended solids by weight to percentage of sludge by volume.
  • For normal sludge, the value of sludge index for Indian conditions is 150 to 350.
  • When there is no re-circulation of sewage, then re-circulation factor is 1.
  • For the same solid content, if the quantity of sludge with moisture content of 98% is X, then the quantity of sludge with moisture content of 96% will be X/2/
  • A pipe which is installed in the house drainage to preserve the water seal of traps is called antisiphonage pipe.
  • In the two pipe system of house plumbing, the pipes required are one soil pipe, one waste pipe and two vent pipe.
  • The pipe which is used to carry the discharge from sanitary fittings like bathrooms, kitchens etc. is called waste pipe.
  • The gas from sludge digestion tank is mainly composed of carbon dioxide.
  • Most of the bacteria in sewage are saprophytic.
  • The process of lagooning is primarily a means of reducing the excessive flow in sewers.
  • The biochemical treatment of sewage effluents is essentially a process of alkalinization.
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