VPE 511: Environment and Environmental Hygiene (2+1)

PURIFICATION TREATMENT OF WATER CARRIED SEWAGE

• The object of a sewage purification works are
• To separate the solids and suspended matter, which are for the most part putrifiable from the fluid portion.
• To purify the fluid portion, so that it can be ultimately discharged into a river or stream with safety and without causing a nuisance and  To dispose of the more solid portion of the sewage which becomes settled out to form sludge.
• The treatment of sewage depends on whether it is generated from residential or industrial area. Sewage from a purely residential town with a good water supply is comparatively easy to treat that from a manufacturing town with a less generous water supply and with the inclusion of industrial wastes presents for more difficulty.
• The volume of sewage is usually stated in gallons per head of population per day, this may very from about 10 gallons up to 100 gallons or even more, depending on the water supply available and the habits of the community under consideration. A common figure for daily dry weather flow is 30-40 gallons per head.
• The sewerage systems may be separate or combined in the first mentioned separate sewers are provided for sewage and for rain water. In the combined system rain water and sewage are carried in one sewer. The latter method is the more common and where it is adopted the quantity of sewage to be dealt with is of course greatly increased in wet weather.