MBR activated sludge viscosity measurement using the Delft filtration characterization method

Viscosity measurements play an important role in activated sludge (AS) characterization, especially with respect to Membrane BioReactor (MBR) operation where low and high shear rates (velocity gradients) occur near the membrane surface and on the bioreactor tank due to the mixing, respectively. Moreover, viscosity plays a role in terms of energy consumption (e.g. pumping and mixing). Therefore, an accurate viscosity relationship as a function of total suspended solids (TSS) and temperature can help to model the behavior of the AS. A total number of 10 municipal and 11 industrial MBR plants throughout Europe were investigated during the period 2007–2009 using the Delft Filtration Characterization method (DFCm). Unlike other literature studies, AS rheology was measured on site, exploiting the resemblance of the DFCm to a tubular rheometer and compared against the results of a rotational rheometer. A new rheological model for the viscosity of AS was developed maintaining the same mathematical structure as previous rheological models made for MBRs. The model proposed in this study is valid for TSS and temperature ranges of 5–20 g L−1 and 10–25 °C, respectively. This model proves that the DFCm unit can be used as a ‘cheap’ rheometer and produce the same results as a rotational rheometer for AS viscosity characterization.