Operation and management of small sewage works.

  • Great Britain. Ministry of Housing and Local Government.
Date:
1965
Catalogue details

Licence: Public Domain Mark

Credit: Operation and management of small sewage works. Source: Wellcome Collection.

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    Unlike a settling tank, the sludge is left in a septic tank for several months and the tank is made large enough to hold the sludge which collects during this time. While it is stored the sludge ferments or “‘digests’’> and is reduced in quantity. The inlets and outlets are baffled, often by the use of tee-pieces, and a crust forms on the surface of the water. The tank is usually covered. 38. When the tank is between one-third and a half full of sludge it is desludged, usually with a cesspool emptier. You should take out only about two-thirds of the sludge and leave the rest behind so that the ripe, fermenting sludge still in the tank ‘‘seeds”’ the freshly settled sludge. If you do not leave enough ripe sludge in the tank the proper fermentation does not take place and the contents of the tank will be likely to smell. Disinfectant should be avoided. It will interfere with the proper action of the tank. 39. When road access to a septic tank is poor, care should be taken to see that the tank is desludged before bad winter weather sets in. The disposal of storm sewage 40. In some districts, rainwater is allowed to run into the foul sewers increasing the flow, which during a heavy rainstorm may be many times the average flow in dry weather. Arrangements have to be made to deal with this extra flow when it arrives at the sewage works. After a short time the mixture of sewage and rainwater will usually be weaker than the foul sewage delivered during dry weather, but at the beginning of a storm it may often be stronger because of the flushing out of deposits which have settled in the sewers. 41. The rate of flow of foul sewage arriving at the disposal works during dry weather will vary from time to time throughout the day and night, and to cope with this variation sewage works are usually designed to deal with about three times the average flow of foul sewage. At works where rainwater arrives in the foul sewers, flows in excess of this rate are diverted by means of a separating weir into storm tanks. The main purpose of these tanks is to store the first flush of foul storm sewage so that it can be pumped back for treatment after the storm. If the storm continues after the tanks are full they are allowed to overflow to the river. When this happens