Digested sludge rheology: Similarities with soft glassy materials

Despite the obvious advantages of anaerobic sludge digestion viz. sludge reduction and sustainable management, it has some drawbacks. In particular, anaerobic digestion produces a complex and unknown residue - sludge - which is difficult to treat and to dewater. Because dewatering mainly involves rheological solid characteristics, this paper focuses on the similarities between these residues with other well-known materials through a series of performing rheological dynamic measurements. By performing strain and frequency sweeps at different concentrations and temperatures in the range from 10 to 60°C, we show that digested sludge exhibits strong similarities with soft glassy materials. The result show a peak in loss modulus - G¿¿- and a monotonic decrease of elastic modulus - G¿- the hallmark of soft glassy materials. These results indicate that we can use all the known characteristics of soft glassy materials to better understand the rheological behaviour of digested sludge. It further provides a basis for future work for the modelling of model materials to simulate real sludge behaviour.