Filtration Performance In Long-term Run And Adsorption Capacity Of Blankened Sand Which Formed In Surface-water Supply Plant

The surface characteristics, filtration performance in long-term run, and the capability in adsorbing Fe, Mn and Sb of darkened sand which formed in surface-water supply plant were studied in this thesis. Results indicated that Mn, Fe, Al were the main elements consisting of the darkened coating of the quartz sand, there was scarcely any microbe at the surface of darkened sand. Quartz sand need three to four years to darkened completely. The specific surface area of darkened sand was nearly 20 times than that of new quartz sand. The acid and alkali resistance tests interpreted that the darkened coating would not dissolve into water in a large range of pH. In filtrate quality according to removal of Mn, Fe and turbidity, Darkened sand exceeded quartz sand a little. 24 inspected quality indexes of the filtrate from filtration with the media met the Standards for Drinking Water (GB5749-85), indicating that the darkened quartz sand could be continuously used as filter media. To solve the problem of sand loss and harden, it is suggested that the diameter of media and the intension of back wash should be enlarged properly, and the time of back wash should be prolonged.In the study of adsorbing Mn, Fe and Sb, it was observed that the capability of adsorbing Fe and Mn of darkened sand was much bigger than that of new quartz sand. The course of adsorbing Fe, Mn and Sbcould be explained by Langergren kinetics, and belonged to the category of ion exchange. The isotherm of Darkened sand adsorbing these three kinds of heavy metal accorded with Freundlich isotherm. Thermodynamics study indicated that the adsorption course is spontaneous, endothermic and unreversible. Adding cation or anion to source water had bad effect on the adsorption of these three kinds of heavy metal, but not evident. pH had obvious influence on the adsorption: the adsorption percentage increased along with the pH value increased in adsorbing Mn, while adsorption percentage has the maximum value under the neutral pH condition in adsorbing Sb. The result was preferable while use tap water , acidic solution with pH=3.0 and alkali solution with pH=12.0 as regenerant. For the convenience of operation,it is suggested to adopt tap water as regenerant.