Laboratory simulation of belt press dewatering: Application of the Darcy equation to gravity drainage
Belt-thickening processes are used for preliminary dewatering of flocculent sludges such as polymer-conditioned wastewater sludges, industrial sludges, and water treatment silts. These processes are also directly or indirectly used as the lead-in step in belt-pressing dewatering of these types of sludges. In the belt press application, improperly drained sludge can yield failure of the subsequent pressing steps. This paper is Part I of a series on the laboratory simulation of belt-pressing dynamics and addresses the mathematics of the gravity drainage of conditioned sludges through short depths on fabric filter cloth. The rate of water drainage through the fabric filter for sludge from a given source and treated with constant polymer doses per dry weight of sludge solids is a function of the total volume of the sample, the solids fraction within the sample, the specific resistance of the forming cake, and the specific resistance of the filter cloth. A drainage rate model that fits the general shape of drainage rate from numerous sludges is derived. Methods for using the proper test volume in batch tests in relation to full-scale dynamic presses are presented. Finally, a simple test method for determining the resistance through the filter cloth on full-scale presses is suggested. Data from 12 test conditions including five types of sludges are analyzed. The model appears to adequately account for volumetric changes, sludge concentration changes, and changes in belt resistance in laboratory drainage tests.
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Document Type: Research Article
Publication date: 01 May 1996
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Water Environment Research (WER) publishes peer-reviewed research papers, research notes, state-of-the-art and critical reviews on original, fundamental and applied research in all scientific and technical areas related to water quality, pollution control, and management. An annual Literature Review provides a review of published books and articles on water quality topics from the previous year. Published as: Sewage Works Journal, 1928 - 1949; Sewage and Industrial Wastes, 1950 - 1959; Journal Water Pollution Control Federation, 1959 - Oct 1989; Research Journal Water Pollution Control Federation, Nov 1989 - 1991; Water Environment Research, 1992 - present.
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