Experimental rheological procedure adapted to pasty dewatered sludge up to 45 % dry matter

Abstract

Wastewater sludge are characterized by complex rheological properties, strongly dependent on solids concentration and temperature. These properties are required for process hydrodynamic modelling but their correct measurement is often challenging at high solids concentrations. This is especially true to model the hydrodynamic of dewatered sludge during drying process where solids content (TS) increases with residence time. Indeed, until now, the literature mostly focused on the rheological characterization of sludge at low and moderate TS (between 4 and 8%). Limited attention was paid to pasty and highly concentrated sludge mainly because of the difficulties to carry out the measurements. Results reproducibility appeared to be poor and thus may not be always fully representative of the effective material properties. This work demonstrates that reproducible results can be obtained by controlling cracks and fractures which always take place in classical rotational rheometry. In that purpose, a well-controlled experimental procedure has been developed, allowing the exact determination of the surface effectively sheared. This surface is calculated by scattering a classical stress sweep with measurements at a reference strain value. The implementation of this procedure allows the correct determination of solid-like characteristics from 20 to 45% TS but also shows that pasty and highly concentrated sludge highlight normal forces caused by dilatancy. Moreover the surface correction appears to be independent of TS in the studied range.

Supplementary In-Depth Analysis of the Waste Activated Sludge Dewatering Process Using a Rheological Analysis

“…When the TS content increases, dominating interactions of sludge transferred from a lubricated regime (indirect contacts) to a frictional regime (direct contact), leading to dilatancy and fractures. Although Mouzaoui, Baudez, Sauceau, and Arlabosse conducted a work aiming to develop experimental rheological procedure adapted to dewatered sludge up to 45% (TS%), it is still debatable to put it in practice . Meanwhile, though the model data fitted with limited TS range (20–62 g), the measured data in the limited range shows close correlations of these variations.…”

“…So, it is imperative to measure the rheological properties of sludge systems with different TS for longitudinal comparison. However, the literature has widely focused on the rheological properties of sludge at only one or few values of TS and few studies were conducted on the dewatering process for a wide range of TS values due to the difficulties of obtaining measurements. , Generally, these results just reflect the structure changes of the sludge system around its initial TS during pretreatments, the messages which track the rheological properties of sludge with different pretreatments during different mechanical dewatering process are still limited.…”

Experimental Investigation of Solar Greenhouse Drying of Hydroxide Sludge under Summer and Winter Climate

“…Thus, this process allows a significant energy saving given that the specific energy consumption of conventional convective dryers varies from 700 kWh/t to 1400 kWh/t of evaporated water from 800 kWh/t. t at 955 kWh/t of evaporated water for conventional conductive dryers [22]. Fig.…”

Rheological characterization of sludge in divided granular-like and pasty states using a granular rheometer

“…The normal stress (σ = F n /πR 2 ) was recorded in parallel with viscoelastic properties. To avoid fracturing, the stress sweep was performed according to the experimental procedure of surface correction developed by Mouzaoui et al [18]. This procedure consists of applying a stress sweep in successive steps of constant dynamic stress of increasing intensity.…”

“…But despite this, only few publications are devoted to the rheological characterization of paste-like and plastic sludge, mainly because of the difficulties to carry out relevant measurements [13][14][15][16][17]. Recently, Mouzaoui et al [18] succeeded to investigate the rheological behaviour of sludge up to its plastic limit (TS=43 wt. %), using a conventional rotating rheometer and without any physical pre-treatment.…”