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

Effect of substrate feeding on viscosity evolution of anaerobic granular sludges

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Effects of physico-chemical factors on the viscosity evolution of anaerobic granular sludge

The rheological properties of anaerobic granular Sludge samples from four full-scale and one lab-scale anaerobic bioreactors were characterized by determining their "limit viscosity" values. These values were deducted from the evolution of the apparent viscosity of granular sludge samples (20 mL) at steady shear rate (200s(-1)) recorded using rotation tests with a wings type measurement cell stirrer Anton-Parr reference: ST24-1D/2V-Q0. The limit viscosity values depended on the applied shear rate, indicating a non-Newtonian behavior of the anaerobic granular sludge types investigated. The effect of variations of physico-chemical parameters such as pH (involving surface charge change), size, surface roughness and TSS content on the evolution of the limit viscosity of an anaerobic granular sludge suspension was investigated. This showed the importance of both quantitative (number of particles in a given volume) as well as qualitative (surface charge or shape) granule-granule interactions on this theological parameter. Moreover, the origin of the granular sludge strongly influenced the limit viscosity value according with different granules characteristics. This work confirms the ability of the rheological parameter "limit viscosity" as an overall parameter to describe the physico-chemical characteristics (TSS, granulometry, origin, and charge) of anaerobic granular Sludge and showed this holds for both sieved (500 mu m) and unsieved sludges

Effect of Na+ and Ca2+ on the aggregation properties of sieved anaerobic granular sludge

Interactions between fine particles (0¿50 ¿m) of anaerobic granular sludge were investigated by studying the effect of Na+ or Ca2+ supply on the evolution of the zeta potential and viscosity of granular sludge suspensions. In the Na+ or Ca2+ concentration range investigated, the Na+ addition affected only slightly the evolution of the viscosity of fine particles of an anaerobic granular suspension. In contrast, Ca2+ addition strongly modified the evolution of the viscosity of the studied anaerobic granular sludge suspension. The use of rheology combined with zeta potential measurements clearly described the physico-chemical interactions between small anaerobic granules and especially the importance of aggregation phenomena that occur between fine anaerobic particles under Ca2+ addition. The positive effect of Ca2+ on the aggregation of non-fed fine anaerobic granular sludge is likely to induce the formation of bigger particles and thus, prevent their wash-out from anaerobic bioreactors

Effect of substrate feeding on viscosity evolution of anaerobic granular sludges

This work aims to describe the effect of the feeding regime of anaerobic activity tests on the limit viscosity (mlim) evolution of the granules. Batch experiments were performed with 3 different sources of substrate: acetate, peptone, and glucose. Despite, the substrate origin was shown to affect the mlim evolution of granules, no clear relationship was found between the mlim evolution, type of substrate and other granule physico-chemical characteristics (i.e. pH; % of Volatile Suspended Solid; concentration of exopolymeric substances, divalent cations, P and S). The origin of granules and the substrate feeding regime modify the surface shape of the granules and may change granule-granule interactions under a shear stress, thus affecting the evolution of the mlim value during long term reactor operation

Effect of substrate feeding on viscosity evolution of anaerobic granular sludges

This work aims to describe the effect of the feeding regime of anaerobic activity tests on the limit viscosity (mu(lim)) evolution of the granules. Batch experiments were performed with 3 different sources of substrate: acetate, peptone, and glucose. Despite, the substrate origin was shown to affect the mu(lim) evolution of granules, no clear relationship was found between the mu(lim) evolution, type of substrate and other granule physico-chemical characteristics (i.e. pH; % of Volatile Suspended Solid; concentration of exopolymeric substances, divalent cations, P and S). The origin of granules and the substrate feeding regime modify the surface shape of the granules and may change granule-granule interactions under a shear stress, thus affecting the evolution of the v value during long term reactor operation

Effect of inoculum and sludge concentration of viscosity evolution of anaerobic granular sludges

The rheological behaviour of granular sludges (diameter 20-315 ¿m) originating from different anaerobic reactors was carried out using rotation tests. The sieved granular sludges suspensions display a non-Newtonian rheological behaviour and the limit viscosity was therefore used as a rheological parameter. The values obtained, which depend on the shear rate used, were strongly influenced by the total suspended solids (TSS) content of granular sludge and an exponential relation was found between the TSS and the rheological parameter limit viscosity. The increase of viscosity as a function of TSS content of the granular sludge as well as the increase of granule size underlines the importance of the interaction between granules in the evolution of this rheological parameter. Significant differences in granular sludge limit viscosity were found for granular sludge of different origins. All measurements performed with 10 g·l-1 TSS granular sludge indicate the ability of the chosen rheological parameter to describe different granular sludge quality

Effect of Na+ and Ca2+ on the aggregation properties of sieved anaerobic granular sludge

Interactions between fine particles (0¿50 ¿m) of anaerobic granular sludge were investigated by studying the effect of Na+ or Ca2+ supply on the evolution of the zeta potential and viscosity of granular sludge suspensions. In the Na+ or Ca2+ concentration range investigated, the Na+ addition affected only slightly the evolution of the viscosity of fine particles of an anaerobic granular suspension. In contrast, Ca2+ addition strongly modified the evolution of the viscosity of the studied anaerobic granular sludge suspension. The use of rheology combined with zeta potential measurements clearly described the physico-chemical interactions between small anaerobic granules and especially the importance of aggregation phenomena that occur between fine anaerobic particles under Ca2+ addition. The positive effect of Ca2+ on the aggregation of non-fed fine anaerobic granular sludge is likely to induce the formation of bigger particles and thus, prevent their wash-out from anaerobic bioreactors