Identification of rheological parameters describing the physico-chemical properties of anaerobic sulphidogenic sludge suspensions

This work determined rheological parameters able to describe the rheological properties of the flocculant sludge presents in sulphidogenic anaerobic bioreactors, i.e. a MBR (membrane bioreactor) and a CSTR (continuous stirred tank reactor). Both sludges displayed a non-Newtonian rheological behaviour with shear thinning properties, slightly thixotropic for a TSS content ranging from 0 to 23 g l−1. Both sulphidogenic sludges displayed pseudoplastic properties. To predict the rheological properties of other sludges, three rheological models (Casson, Bingham and Herschel–Buckley) were selected and fitted to the experimental rheological data obtained. The mathematic equations of these three models give seven rheological parameters. To select relevant rheological parameters, exponential and second-order polynomial equations were tested to evaluate the relationship between the rheological parameters and the sludge TSS content. These two last variables were statistically fitted with a second-order polynomial correlation, which allows to select rheological parameters able to describe the evolution of the sludges in both bioreactors. The Bingham model applied on the pseudo-Newtonian area of a rheogram gives the more suitable rheological parameters to describe the evolution of the rheological properties of anaerobic sulphidogenic flocculant sludge. The selected rheological parameters of the sulphidogenic sludges are affected by the bioreactor type and its operation time. This is likely linked to changes in microbial consortia involving a change in biomass morphology and a decrease in floc strength.