Thermo-physical properties of synthetic mucus for the study of airway clearance.

In this article, dynamic viscosity, surface tension, density, heat capacity and thermal conductivity, of a bronchial mucus simulant proposed by Zahm et al., Eur Respir J 1991; 4: 311-315 were experiementally determined. This simulant is mainly composed of a galactomannan gum and a scleroglucan. It was shown that thermophysical properties of synthetic mucus are dependant of scleroglucan concentrations. More importantly and for some scleroglucan concentrations, the syntetic mucus, exhibits, somehow, comparable thermophysical properties to real bronchial mucus. An insight on the microstructure of this simulant is proposed and the different properties enounced previously have been measured for various scleroglucan concentrations and over a certain range of operating temperatures. This synthetic mucus is found to mimic well the rheological behavior and the surface tension of real mucus for different pathologies. Density and thermal properties have been measured for the first time. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 3025-3033, 2017.

Effect of exo-polysaccharide concentration in the rheological properties and settling ability of activated sludge.

The non-Newtonian properties of activated sludge (AS) suspension lead to transfer limitations (oxygen, substrate...) and operation difficulties in Waste Water Treatment Plants (WWTP). The current approach involves assuming the sludge behaves like water on a rheological point of view, and then oversizing pumping and aeration devices, which represent over 60% of the operating cost in WWTP. The objective of this work is to understand the effect of bioflocculation on the rheological properties and the settling ability of AS suspensions, by means of variations in concentration of exo-cellular polysaccharides. Experiments have been conducted in a 20 L laboratory scale bioreactor at a constant retention time of 20 days and with a total suspended solid concentration between 15 and 20 g L(-1). The bioreactor was fed with a synthetic substrate at a constant mass loading rate of 0.3 kg(DCO) kg(-1)(TSS) d(-1). Our results show that increasing the exo-polysaccharide (EPS) concentration from 10 to 80 mg g(-1)(TSS) leads to an increase in shear-thinning properties of AS. An improvement of the settling ability is also obtained, at least when the EPSs increase from 10 to 45 mg g(-1)(TSS). Above 45 mg g(-1)(TSS) of adsorbed polysaccharides, the settling ability seems to decrease again.