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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    sludge being removed. This method avoids passing more water to the sludge treatment plant than is absolutely necessary. 31. Upward flow tanks should be desludged at least twice a week or the draw-off pipe may become choked with very thick sludge. If this happens shut off the flow to the tank and clear the pipe by using a plunger through the rodding eye or in the tank itself. If plunging fails it may be necessary to get a jet of water or compressed air down the pipe to break up the dense sludge. In extreme cases you will have to empty the tank with a mobile pump and dig out what has accumulated. 32. Failure to desludge the tanks or to remove the scum often enough will give rise to the symptoms and troubles referred to in paragraphs 27 and 28. If the desludging of upward flow tanks is carried out too frequently the sludge will contain too much water and take longer to dry. The best time interval for any particular tank can only be determined by experience. 33. If, at normal daytime flows, any lengths of the outlet weirs are persistently dry you should report it to the foreman or the surveyor. Mechanically desludged tanks 34. Some tanks are specially designed for mechanical desludging. There are two basic types of machine. One operates in a rectangular tank and scrapes the sludge along the bottom into hoppers at the inlet end. The other is designed to work in a circular tank in which the sewage enters at the centre and leaves over a continuous weir running around the outside edge of the tank; the floor slopes gently towards the centre and the sludge is scraped to a central hopper by a rotating scraper. With both types arrangements for mechanical skimming and removal of floating matter are often included. 35. The sludge is removed from the hoppers by water pressure in the same way as from upward flow settling tanks, and you will need to do it in the same way. 36. The machinery for desludging tanks varies considerably, and you should ask for the maker’s instructions on operation and maintenance. Septic tanks 37. Asmall works may have a septic tank instead of a settling tank.