LABORATORY TESTS TO OPTIMIZE SLUDGE COAGULATION / FLOCULATION PROCESSBEFORE THICKENING OR DEWATERING

摘要

This work deals with a new laboratory protocol to optimize sludge coagulation/floculation process inrnview of their thickening on a drainage table or their dewatering in a filter-press, a decanter centrifugernor a belt filter press. The aim of this work is to define the mixing conditions between polymer andrnsludge and the floc characterization tests related to the treatment the flocs undergo in a thickening orrndewatering equipment.rnThe methodology consisted in dispersing quickly the polymer in the sludge with a high shearrnand then to let the flocs grow more slowly with a low speed mixing. The control of the torque duringrnthe mixing enabled to easily repeat the protocol. The kinetics of floc growth was followed with arnTurbiscan apparatus. It enabled to define the best hydrodynamic conditions of sludge flocculation.rnDifferent laboratory testing methods such as gravity drainage tests, Capillary Succion Time, filtrationcompressionrnand centrifugation tests were then made to evaluate the flocs resistance to compressionrnand shear and their ability to filtration and dewatering.rnBiological activated sludges coming from different sewage treatment plants were used for thernexperimental study. A significant part of this work concerned the selection of the tests related to arntechnique and the validation of these tests at industrial scale. It was found that the protocol used is arngood comparative method to choose the best polymer and its optimum dose for each thickening orrndewatering technique. Performances of a gravity belt thickener can be well predicted by a gravityrndrainage test and Severin Model. A compression-filtration test is sufficient to simulate a filter-pressrnand to obtain the same performances at laboratory and industrial scales . Nevertheless,rncentrifugation tests and filtration-compression test at variable pressure and short residence timernoverestimate the dryness of the sludge respectively for a decanter centrifuge and a belt filter pressrnbecause actual shear forces are badly taken into consideration for these two techniques.