Three-dimensional computational fluid dynamic modelling of a facultative lagoon

Abstract

A series of facultative lagoons operated by Thames Water treating industrial wastewater in Thailand were found to be performing poorly, particularly with respect to the removal of biological oxygen demand (BOD). A review of the design parameters for the site found that all the lagoons are of a sufficient area for the flow and BOD load. However, observations of the lagoons suggested that there may be significant hydraulic short-circuiting. Computational fluid dynamics (CFD) modelling was therefore carried out on one of the lagoons to establish the hydraulic regime. Two consecutive simulations were carried out, both with and without baffles; the first to establish steady flow conditions, and the second using a chemical species transport model to obtain the residence time distribution (RTD). The results of the modelling indicate that the lagoons do currently suffer from significant short-circuiting, and large dead-zones are present. The installation of baffles in the CFD model improved the plug-flow characteristics of the lagoons, substantially reducing the short-circuiting and the size of the dead-zones. It has therefore been concluded that the installation of baffles in the lagoons will lead to an improvement in their performance, by increasing the retention time of the system.

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.…”

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

“…Vega et al (2003) took the wind into account and concluded its influence is negligible. 2D models were soon shown to be ill-adapted to the modelling of WSPs which, despite they are shallow water bodies, are subjected to influential three-dimensional mechanisms (Wood 1997;Salter 1999;Salter et al 2000;Brissaud et al 2003).…”