Résumé
The aim of this work is to investigate the rheological behaviour of MBR sludge for prolonged sludge retention time and during unsteady state conditions. The role of the total suspended solids and of the soluble organic matter is specifically studied through two running periods characterized by different organic loads and/or solid retention times. Diverse theological parameters are examined. They are obtained from flow measurements carried out for an extent range of shear stress values.
The obtained results show clearly that operating conditions capable of changing the total suspended solid (TSS) and soluble organic compound (COD) concentrations modify the theological behaviour of the sludge. In comparison with the TSS concentration, the soluble organic compounds greatly affect the cohesion and the rigidity of the sludge three dimensional network. On the other hand. the COD concentration and the TSS content have equivalent quantitative influence on the theological parameters characterizing the flow of the sludge.
The results obtained are of great importance because operating conditions leading to the modification of the soluble microbial product concentration, and of the sludge rheological characteristics in the reactor, can strongly modify not only the mixing and aeration performances but also the membrane fouling of the MBR unit. (C) 2009 Published by Elsevier B.V.