Transparent polymers to emulate the rheological properties of primary, activated, and digested sludge

Abstract

Abstract Understanding the rheological characteristics of sludge is important for design and operation of water and wastewater treatment units including stirrers, mixers, pumps, and separators. Studying the rheological characteristics of real sludge involves health risks and complexity due to opaque nature of sludge and its time evolution caused by microbial activity and aging. Researchers have applied various simulants such as clay, minerals, and gels to prepare synthetic sludge and to perform a lab-scale study on rheological properties and flow behaviour of real sludge. Some of previous studies have ignored the stability and rheological characteristics of simulant fluids, which might lead to less reliable results. Therefore, selection of a safe, cheap and stable alternative that can mimic rheological behaviour of real sludge is still open and challenging. The proposed study examined the pH sensitivity, zeta potential characteristics and rheological properties of sodium carboxymethyl cellulose, polyethylene glycol, sodium alginate, and xanthan gum as popular model fluids with different concentrations (0.1, 0.5, 1, 1.5, 2, and 3\u2009wt%) in details. A comparison of rheological properties of these fluids with the rheology of different types of sludge indicated that xanthan gum is a preferred simulant fluid that mimic the behaviour of sludge for the shear rate below 100\u2009s−1. Analysis of zeta potential and pH sensitivity indicates that xanthan gum is also a resistant solution to pH changes and agglomeration. In addition, it replicates sludge behaviour in terms of viscosity, flow curve, and Herschel–Bulkely parameters. Nevertheless, xanthan gum does not support thixotropy and viscoelastic characteristics of sludge.