Abstract
Viscosity and rheological behaviour of sewage as well as sludge are essential while designing apparatuses and operations employed in the sewage treatment process and its processing. With reference to these substances, the bio-suspensions samples of three size fractions ((i) 150÷212 μm, (ii) 106÷150 μm and (iii) below106 μm) of dry grass in water with solid volume fraction 8%, 10% and 11% were prepared. After twenty four hours prior to their preparation time, the suspension samples underwent rheometeric measurements with the use of a rotational rheometer with coaxial cylinders. On the basis of the obtained results, flow curves were plotted and described with both the power model and Herschel-Bulkley model. Moreover, the viscosity of the studied substances was determined that allowed to conclude that the studied bio-suspensions display features of viscoelastic fluids. The experimentally established viscosity was compared to the calculated one according to Manley and Manson equation, recommended in the literature. It occurred that the measured viscosity values substantially exceed the calculation viscosity values, even by 105 times. The observations suggest that it stems from water imbibition of fibrous vegetal particles, which causes their swelling and decreases the amount of liquid phase in the suspension.
Highlights
Sewage treatment is a very complex process because it consists of many operations, e.g. piping transport, mixing, aeration or sedimentation [1]
In order to achieve a correct design of the apparatuses within the process of sewage processing, knowledge of these substances viscosity in various process conditions is essential
The major conclusion stemming from the conducted analysis concerns the duration of vegetal particles presence in a given multiphase system, which can affect the viscosity of the sewage and their rheological behaviour
Summary
Sewage treatment is a very complex process because it consists of many operations, e.g. piping transport, mixing, aeration or sedimentation [1]. The viscosity influences mainly the suspensions flow pattern, their flow resistances, the phenomena of heat transfer and the velocity of solid particles settling or gas bubbles lifting. Its value may result from the solid concentration, the solid properties and the shear time and shear rate bound up with the flow velocity in a pipe or a mixing intensity in a tank. Fluctuations of suspensions viscosity can be verified due to the rheometeric measurement results of these fluids. The rheometeric measurements are the most state-of-the-art and desirable in the wastewater treatment sector as well as in many other fields of industry what is mentioned by the authors of the papers [3,4]
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