Abstract
Aeration process in the waste activated sludge treatment accounts for 75% of total energy consumption of the treatment plant. The main purpose of the aeration process is to enhance the biodegradation of the liquid waste. Gas bubbles, rising through the liquid, improves mixing, reduces inhomogeneities in the treatment tank and enhances biological reactions. Thus aeration intensity and several physicochemical properties of feed such as viscosity, total suspended solids, and surface charge play a significant role in the biological reaction.This paper examines the impact of the gas injection rate on some physicochemical properties of waste activated sludge namely rheological properties, suspended solids, soluble COD (sCOD), surface tension, and zeta potential. The impact of four different gas flow rates on four different concentrations of waste activated sludge properties was analysed.The results showed that in linear viscoelastic regime the viscous and elastic modulus decreases linearly with an increase in gas flow rate. The amount of stress imposed by gas injection also showed a direct relationship with gas velocity. Gas injection also showed a substantial impact on soluble COD, suspended solids, and zeta potential. Additionally, a linear relationship was observed between the percentage change in the above mentioned physical properties and stress imposed by gas injection. These results confirm that gas injection produces additional shear impacting sludge physicochemical properties and therefore changes its rheological behaviour. The extra stress induced by gas injection can be predicted using a simple model based on sludge concentration and gas velocity.
Highlights
The waste activated sludge process is the most versatile and commonly used biological treatment (Seyssiecq et al 2008)
The results showed that in linear viscoelastic regime the viscous and 35 elastic modulus decreases linearly with an increase in gas flow rate
Waste activated sludge is composed of water, microorganisms, and 65 macromolecules grouped in bioflocs (Laspidou and Rittmann 2002)
Summary
The waste activated sludge process is the most versatile and commonly used biological treatment (Seyssiecq et al 2008). The efficiency of the waste activated sludge process depends upon an aeration operation. The oxygen transfer rate in the aeration tank decreases with an increase in the total solid concentration of sludge and strongly influences the efficiency of the process (Rosenberger et al 2002). This is because with increasing solid concentration of sludge results in an increased viscosity of sludge that causes variations in system hydrodynamics as and impacts on bubble buoyancy, bubble shape and turbulence Waste activated sludge is composed of water, microorganisms, and macromolecules grouped in bioflocs (Laspidou and Rittmann 2002). Since the sludge characteristics and rheology affect each other, the impact of aeration on rheology and sludge physical properties should be considered when studying the sludge flow behaviour in the aeration tank
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