Application of CFD modelling to study the hydrodynamics of various anaerobic pond configurations

Abstract

The simulation of hydrodynamics and transport phenomena in waste stabilization ponds is a developing tool worth studying in order to understand their internal processes and interactions. Pond design involves several physical, hydrological, geometric and dynamic variables so as to provide high hydrodynamic efficiency and maximum substrate utilization rates. CFD modelling allows the combination of these factors to predict the behaviour of ponds having different configurations. The two-dimensional depth-integrated model MIKE 21 was used in this study to simulate hydrodynamic and advection-dispersion processes in a full-scale anaerobic pond (AP) located in southwest Colombia. A set of 12 configurations including sludge contents, inlet-outlet positioning, baffling and pond geometry were modelled. Results showed that a crosswise (diagonally opposite) inlet-outlet layout, a length-to-breadth ratio of 2:1, plus provision of two cross baffles at 1/3 L and 2/3 L were the most effective measures to improve overall AP hydrodynamics and dispersion patterns.

Impact of Hydrodynamic Reconfiguration with Baffles on Treatment Performance in Waste Stabilisation Ponds: A Full-Scale Experiment

“…There are numerous studies that have investigated the link between baffled ponds and treatment efficiency, mainly through the use of hydrodynamic and/or laboratory physical models e.g., [18][19][20][21]. In general, previous hydrodynamic modelling has suggested that baffles will significantly improve pond hydraulics, and some of these models have been validated with lab-scale models or prototypes [22][23][24][25][26][27][28]. However, despite the value provided through model validation using small-scale controlled environments, there has been a lack of studies that demonstrate and validate the effectiveness of baffles at the operational pond-scale.…”

“…Furthermore, while modelling has shown that baffles improve pond hydraulics, there is a lack of consensus in recommending the best configuration for flow improvement e.g., [18,22,24,25]. Here we define flow optimisation as maximising pond residence time through a decrease in short-circuiting.…”

“…Here we define flow optimisation as maximising pond residence time through a decrease in short-circuiting. For example, two baffles perpendicular to the inflow gave the optimum treatment performance (e.g., residence time, coliform removal, biological oxygen demand (BOD) removal) in some cases [24,25], while another suggested two or four baffles perpendicular to the inlet [18]. Another study found a single subsurface baffle or island baffle placed in front of the inlet was the best design option [22].…”

Significance of buoyancy in turbulence closure for computational fluid dynamics modelling of ultraviolet disinfection in maturation ponds

“…Important CFD studies have also been done in other types of waste stabilisation ponds (Salter et al, 2000;Baléo et al, 2001;Vega et al, 2003;Sah et al, 2011;Passos et al, 2014), aquatic ponds (Peterson et al, 2000), UV chemical reactors (Wols et al, 2015;Xu et al, 2015), and storm water detention ponds (Khan et al, 2013). With the improvement in CFD and computing resources, increasingly complex models are becoming prevalent.…”

Taking wind into account in the design of waste stabilisation ponds

“…RTD and WSP performance are better evaluated through hydrodynamic numerical modelsinstead of conceptual models -that compute water temperature and velocity as well as solute or microorganism concentrations, from the equations describing the involved physical and biological processes and non steady-state boundary conditions. Two-dimensional (2D) hydrodynamic models were initially used to investigate the influence of pond design, considering a steady state regime and no meteorological influence (Wood et al 1995;Persson 2000;Vega et al 2003). Vega et al (2003) took the wind into account and concluded its influence is negligible.…”