title: Clear model fluids to emulate the rheological properties of thickened digested sludge.
abstract: Optimising flow processes in wastewater treatment plants requires that designers and operators take into account the flow properties of the sludge. Moreover, due to increasingly more stringent conditions on final disposal avenues such as landfill, composting, incineration etc., practitioners need to produce safer sludge in smaller quantities. Anaerobic digestion is a key treatment process for solids treatment and pathogen reduction. Due to the inherent opacity of sludge, it is impossible to visualise the mixing and flow patterns inside an anaerobic digester. Therefore, choosing an appropriate transparent model fluid which can mimic the rheological behaviour of sludge is imperative for visualisation of the hydrodynamic functioning of an anaerobic digester. Digested sludge is a complex material with time dependent non-Newtonian thixotropic characteristics. In steady state, it can be modelled by a basic power-law. However, for short-time processes the Herschel-Bulkley model can be used to model liquid-like properties. The objective of this study was to identify transparent model fluids which will mimic the behaviour of real sludge. A comparison of three model fluids, Carboxymethyl Cellulose (CMC), Carbopol gel and Laponite clay revealed that these fluids could each model certain aspects of sludge behaviour. It is concluded that the rheological behaviour of sludge can be modelled using CMC in steady state flow at high shear rates, Carbopol gel for short-time flow processes and Laponite clay suspension where time dependence is dominant.
authors.affiliation: Rheology and Materials Processing Centre, Department of Chemical Engineering, RMIT University, Victoria 3001, Australia. nicky.eshtiaghi@rmit.edu.au
authors.forename: Nicky
authors.initials: N
authors.lastname: Eshtiaghi
authors.forename: Shao Dong
authors.initials: SD
authors.lastname: Yap
authors.forename: Flora
authors.initials: F
authors.lastname: Markis
authors.forename: Jean-Christophe
authors.initials: JC
authors.lastname: Baudez
authors.forename: Paul
authors.initials: P
authors.lastname: Slatter
mesh_terms: D008962:Models, Theoretical; D012212:Rheology; D012722:Sewage
chemical_list: D012722:Sewage