Vane geometry for measurement of influent rheological behaviour in dry anaerobic digestion

The knowledge of the rheology of influents involved in dry anaerobic digestion is an essential factor for process optimization. Despite this fact, it is difficult to characterize the rheological behaviour of these influents with high total solid (TS) content. Indeed, standard methods of rheological measurements are poorly adapted to these influents because of the sliding effects observed during the measurements. In this study, we used a non-standard method, the Vane geometry, for its particularity to limit the sliding effects. Two types of measurements were carried out on potato influents of 18–35% TS, extracted from the digesters. The first measurement was to submit to the sample a rising shear velocity ramp from 0 to 200 s−1 at 37 °C and 55 °C. The results of these measurements show a good correlation between the rheograms and Herschel-Bulkley model and we deduced a pseudoplastic threshold behaviour. The second measurement was performed in oscillations at 10 Hz at 25 °C, 37 °C and 55 °C. The results show different evolutions of the elastic G′ and viscous G″ modulus as a function of temperature. There is a crossing of G′ and G″ at 25 °C, G′ greater than G″ at 37 °C, and finally G′ and G″ forming a plateau at 55 °C, characteristic of a gel. The knowledge of these rheological behaviour is crucial for the design and operating instructions of anaerobic digestion reactors for influents with high TS content. The Vane geometry would, therefore, be an effective tool for characterizing the rheological behaviour of influents in dry anaerobic digestion.