Towards advanced aeration modelling: from blower to bubbles to bulk

Abstract

Aeration is an essential component of aerobic biological wastewater treatment and is the largest energy consumer at most water resource recovery facilities. Most modelling studies neglect the inherent complexity of the aeration systems used. Typically, the blowers, air piping, and diffusers are not modelled in detail, completely mixed reactors in a series are used to represent plug-flow reactors, and empirical correlations are used to describe the impact of operating conditions on bubble formation and transport, and oxygen transfer from the bubbles to the bulk liquid. However, the mechanisms involved are very complex in nature and require significant research efforts. This contribution highlights why and where there is a need for more detail in the different aspects of the aeration system and compiles recent efforts to develop physical models of the entire aeration system (blower, valves, air piping and diffusers), as well as adding rigour to the oxygen transfer efficiency modelling (impact of viscosity, bubble size distribution, shear and hydrodynamics). As a result of these model extensions, more realistic predictions of dissolved oxygen profiles and energy consumption have been achieved. Finally, the current needs for further model development are highlighted.

Microalgae and cyanobacteria modeling in water resource recovery facilities: A critical review

“…Therefore, the combination of both parameters (i.e., the local mass transfer coefficient and the interfacial area) is often considered; this combined coefficient is typically referred to as k L/G a. The prevalence of aeration in the activated sludge process has resulted in extensive in situ determination of the oxygen-specific k L a value (i.e., k L a O2 ) (Amaral et al., 2017; Kayser, 1979) as well as models to describe it (Gillot et al., 2005). Overall mass transfer coefficients for other gases with low solubility (e.g., CO 2 ) are usually calculated from the oxygen transfer rate using Higbie's penetration theory (Eq.…”

Alpha factor determination in a pilot scale sidestream shortcut nitrification process

“…Another potential aspect of observed changes is presence of organic polyelectrolyte in the reject water. Polyelectrolyte is used to improve sludge dewatering efficiency and its presence may lead to influence viscosity of the mixed liquor which determines resistance the bubble experiences when travelling and thus increase observed alpha value [9].…”

Modelling solution for estimating aeration energy of wastewater treatment plants

“…Amerlinck et al (2016) also notes the issues of commonly used oversimplified energy consumption models and developed a dynamic model for predicting the energy costs of a diffused aeration system, based on the physical characteristics of the system, water depth and the airflow demand imposed by the control system. Amaral et al (2017) discussed different components of the aeration system models and reasoned why more complete models are needed for realistic depictions of the process. Amaral et al (2017) state that the entire piping network should be modelled for accurate predictions of the dynamic process, but also state that potential simplifications should be studied.…”

“…Amaral et al (2017) discussed different components of the aeration system models and reasoned why more complete models are needed for realistic depictions of the process. Amaral et al (2017) state that the entire piping network should be modelled for accurate predictions of the dynamic process, but also state that potential simplifications should be studied. In contrast to the modelling approaches described in (Juan-García et al 2018), (Amerlinck et al 2016) and (Amaral et al 2017).…”

“…Amaral et al (2017) state that the entire piping network should be modelled for accurate predictions of the dynamic process, but also state that potential simplifications should be studied. In contrast to the modelling approaches described in (Juan-García et al 2018), (Amerlinck et al 2016) and (Amaral et al 2017). Harja et al (2016) used a very simplified approach for modelling the aeration distribution system, which was based only on the resistance coefficients of the pipelines and valve positioning to model the pressure system.…”