| 摘要 |
<p>Apparatus 1 for treating a fluid, in this case wastewater, comprising a vessel or tank 2, means 3 to supply the wastewater in an alternating sequence to the vessel 2, anda means 4 for oxygenating the bed of granular media 5 to provide aerated filter media. The filter bed is aerated during operation by air, oxygen enriched air or other gas being introduced at or adjacent the base (as viewed) of the bed through the means 4, which may be a perforated manifold, diffuser or the like extending substantially over the whole surface area of the bed 5. Also the bed 5 is a granular media such as natural minerals or blast furnace slag media to the surface of the discrete particles of which is attached bacteria and micro-organisms (a biomass) which effects treatment of the fluid. The influent at 3 derived from sewage is counter current to the air, and is particularly a non-nitrified influent namely wastewater that has previously been treated to reduce the BOD (biological oxygen demand) and suspended solids concentrations. The blast furnace slag media 5 has an average particle diameter of 2.8-4.0mm and a porosity of 13.9%. In carrying out the process the periodic reversal of the flow through the filter bed maintain the concentration gradient of the micro-organisms (biomass) substantially uniform as a desired concentration of micro-organisms throughout the depth of the bed under all operating conditions in the embodiments illustrated. This provides for a uniform, efficient treatment of the sewage. <IMAGE></p> |
