Effect of solution physical chemistry on the rheological properties of activated sludge

Abstract

Knowledge on rheological properties of sludge is important for the design of pumping and transport facilities and as a tool in process control during treatment. Concentrated activated sludge is known to behave as a non-Newtonian material. The contribution to non-Newtonian behaviour is believed to originate from the colloidal properties of solids more than from the molecular properties of the suspension. Considering that the colloidal properties of sludge depend on factors like pH, conductivity, solids concentration and flocculation properties, this study examines the effects of these variables on the rheology of activated sludge. Results show that the rheograms obtained fit best to a power law model indicating that the flow of activated sludge can best be expressed by the pseudoplastic flow model. It is also observed that the apparent viscosity increases sharply with the increase of solids concentration. From the pH values studied, the one that causes the lowest viscosity is the pH 5.5. As the pH increases, the viscosity measured increases considerably. This makes sense considering that the isoelectric point of bacteria is at pH 2-4. Conductivity is also found to affect the viscosity greatly; such that as the conductivity increases, the apparent viscosity decreases. Finally, experimental results reveal that the presence of extracellular polymers and the flocculated nature of activated sludge affect its viscosity.

Effects of Temperature, Polymer Dose, and Solid Concentration on the Rheological Characteristics and Dewaterability of Digested Sludge of Wastewater Treatment Plant (WWTP)

“…Thermal energy results in change of the shape and size of flocculated particles, and the degree of dispersion of the soluble organic content of sludge. These changes directly influence the rheological properties of digested sludge during dewatering (Sanin 2002). Viscosity generally lowers with higher temperature and shear rate, and a similar trend was reported by many researchers (Farno et al 2013;Eshtiaghi et al 2013;Hasar et al 2004;Yeneneh 2014;Hong et al 2015Hong et al , 2016.…”

“…Total chemical oxygen demand was determined by using oxidation method with HACH COD reagent and colorimetric analysis on ORION UV/Vis spectrometer (Li et al 2008). pH was measured with WP-90 and WP-81 conductivity/ TDS-pH/temperature meter equipped with a glass electrode (Sanin 2002).…”

“…The existence of solids within fluid is responsible for the shearthinning flow behavior. The existence of solids within a fluid is the major reason for the increase in the fluid viscosity (Sanin 2002). Sludge characteristic curve for low solid concentrations differ from that for high solid concentration where there is a strong interaction between solid particles.…”

Rheology and Microbiology of Sludge from a Thermophilic Aerobic Membrane Reactor

“…The properties of activated sludge, such as MLSS concentration, particle size distribution and shape, interaction among particles, flocculation ability, and surface physicochemical characteristics, all have effects on rheology and, thus, on the kind of model most efficient in describing the sludge rheological profile and on the values of the preferable model parameters [49,69].…”

Removal of dyes by adsorption on magnetically modified activated sludge

“…The bacteria present in the activated sludge have isoelectric points between pH 2 and 4, and thus, their surface will be negatively charged at higher pH (Sanin 2002). Some pretreatment processes can modify the adsorption capacity of the microbial biomass, such as autoclaving as high-temperature treatment causes cell rupture with a consecutive increase in surface area (Solis et al 2012).…”