Shallow tubes are very efficient sedimentation devices. Two basic tube configurations have been used: essentially horizontal, and steeply inclined. Sludge is removed from the essentially horizontal tubes by automatically draining them each time the filter backwashes and refilling them with filter backwash water. Over 20 water treatment plants using these horizontal tubes with sedimentation detention times of less than 10 minutes with capacities of 20‐2,000 gpm are now in operation. In tests described in this paper, a plant providing flocculation, tube sedimentation, and mixed media filtration, produced potable water (0.1 JU turbidity) from a raw water turbidity of 1,000 JU with an overall plant detention time of 16 minutes. Flow distribution analyses demonstrate that the shallow horizontal tubes enable good flow distribution to be readily achieved.
Tests were begun in 1964 to evaluate the efficiency of tube configurations as sedimentation devices and to evaluate means of sludge removal. Preliminary tests with single tubes of various sizes quickly demonstrated that they were efficient sedimentation devices. During these preliminary tests, it was found that the accumulated sludge could be readily removed by periodically draining the tubes, if they were inclined slightly in the direction of flow. An angle of inclination of 5 degrees was found to be adequate for sludge removal by gravity. The potential merits demonstrated in the preliminary tests resulted in the detailed studies that are described in this paper.
Medens Forekomsten af store, løse Flager af Skrivekridt (brokket Kridt) i Istidsaflejringerne paa Sjælland har været kendt siden Bredsdorffs Dage, blev Tilstedeværelsen af lignende Glacialflager af den graa, paleocæne Mergel (Kertemindemergel) først paapeget Hundrede Aar senere af V. Milthers 1923 nemlig i Egnen Sydvest for Holbæk mellem Regstrup og Knabstrup. Fra to Mergelgrave ved Dorthealyst og Hanerup var der i Aarene 1919-1920 blevet indsendt et Antal Mergelprøver til Analysering i Danmarks geologiske Undersøgelses Laboratorium, og Resultaterne af Analyserne af dette graa, fede, stenfrie Ler viste meget høje Procenttal for kulsur Kalk, idet over Halvdelen af Analyserne angav mellem 60 og 75% kulsur Kalk i Tørstof. I Aaret 1921 undersøgtes Mergellejet ved Hanerup af Det danske Hedeselskabs Mergelvæsen, hvorved der paavistes ret udstrakte Mergellag af i det mindste 11 m Tykkelse og med et Indhold af kulsur Kalk paa henimod 70%.
The exchange of water between the Baltic and the ocean through the Danish Sounds gives rise to a system of currents. The individual currents are dependent on outflow, tides, meteorological factors, bottom relief, etc. The rate of the surface currents is regularly measured at the light-ships, while the rate of the bottom currents is only measured occasionally. Bottom currents are accordingly rather unknown, and few average velocities have been published.The present paper deals with a particular bottom deposit observed in Danish Sounds. It consists of large lumps or »boulders« of clay (e.g. Tertiary clay, Interglacial clay or Glacial till) embedded in normal marine sand and gravel. A »clay boulder« conglomerate of this kind was exposed for a short time at the bottom of the Lillebælt during the construction of the Lillebælt Bridge (fig. 1). The »clay boulders« were in this case derived from the Tertiary Lillebælt clay.Recent investigations of the Storebælt and The Sound with the Kullenberg Piston Core Sampler revealed that a similar sediment is found also in these areas. However, the cores generally display alternation of glacial till and marine shell bearing sand, because the diameter of the Piston Corer is smaller than that of the majority of the »till boulders«. (fig. 2).The clay boulder conglomerates on the present sea bottom of the Danish Straits are evidence of rather strong submarine erosion and redeposition. It is suggested that erosion is particularly efficient along the submarine channels, and that the deep hollows are mainly due to submarine erosion.
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