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

Abstract

Abstract:Wastewater infrastructure is expensive to build and maintain, and there is a need to focus on improving and modernising existing infrastructure before large capital investments are made to service future population needs. Waste stabilisation ponds (WSPs) are used worldwide for the treatment of wastewater, but their performance is significantly affected by poor hydraulic control. Hydraulic reconfiguration of ponds is a possible solution to this problem, whereby the flow is controlled and short-circuiting is reduced. There is evidence to suggest that this approach has the potential to increase treatment performance, however in the absence of full-scale validation it is difficult to generalise this to a wide range of sites. For example, there is no consensus on the best baffle configuration to optimise hydraulic performance. The main objective of this study was to conduct a full-scale experiment of baffles in a WSP, and to investigate their impact on hydraulic performance. To achieve this objective, the approach combined high-resolution pond bathymetry and 2D hydrodynamic modelling, assessed with hydraulic indices, to determine the optimal baffle configuration for the site; it was shown that three baffles perpendicular to the inflow provided the greatest increase (up to 24%) in mean residence time. This configuration was then implemented in a working WSP. The effects of the baffles on the pond were then assessed using a combination of field tracer testing, revealing an increase in mean residence time of at least 20%, and further hydrodynamic modelling. Through the addition of wind data into the hydrodynamic model, it is shown that baffles not only improve the flow, but also attenuate the effect of wind on pond hydraulics. While the conclusions of this study are site-specific, the implementation of site-specific solutions is important for progress towards optimal pond design. The approach developed here is easily transferrable for use on other sites, and will enhance our ability to plan, design and operate WSP systems in the future.

High-Resolution Bathymetry Mapping of Water Bodies: Development and Implementation

“…Applying this to sludge management, a CFD model could be used to determine the differences between different sludge infill scenarios, for example, the current operating sludge distribution in a pond versus the same pond with no sludge; this has been demonstrated in Coggins et al (2017). Modeling with high-resolution bathymetric data in WSPs is very promising, and with the addition of wind forcing (such as in: Shilton and Harrison, 2003), will become a useful diagnostic and predictive tool for existing and new systems, respectively; this could also extent to the design of baffles for existing/new systems, as demonstrated in Coggins et al (2018). Therefore, the addition of high-resolution bathymetry data is a step in the right direction for more spatial accuracy in the CFD modeling of WSP systems.…”

“…ROVs may also be applied to small to medium sized water bodies, such as lakes and stormwater retention wetlands, drinking water reservoirs, rivers, pools, channels, and recreational and commercial ports. The improvement in spatial resolution of pond bathymetry data alone will greatly improve models used to understand pond hydraulics and how sludge accumulation and geometry affect performance (Passos et al, 2016;Coggins et al, 2017Coggins et al, , 2018; these could in turn be used to develop new WSP coupled models of hydraulics and biology. Thus, the main objective of this study was to assess the performance of a ROV with GPS-equipped sonar to measure sludge height in a WSP, with the aim to develop it to a point where it could be implemented for research and within industry.…”

The small, the big, and the beautiful: Emerging challenges and opportunities for waste stabilization ponds in Australia

“…In addition to addressing safety concerns surrounding sludge data collection, the data collected with the ROV can be input into computational fluid dynamics (CFDs) models of WSPs. A validated two‐dimensional model has been used for the assessment of the impact of sludge accumulation and distribution in WSPs (Coggins et al, ), as well as for the design and assessment of baffles to improve pond hydraulics (Coggins, Sounness, Zheng, Ghisalberti, & Ghadouani, ). By improving the accuracy of WSP models, researchers and pond managers will be better placed to assess current hydraulic performance, design new ponds, design retrofits of current assets, and plan future upgrades.…”

“…Until recently, however, there have been no published studies to demonstrate and validate these findings at the fully operational pond‐scale. In Western Australia, a full‐scale hydrodynamic reconfiguration of a pond was trialed, using an approach that combined high‐resolution pond bathymetry and 2D hydrodynamic modeling (Coggins et al, ). Through this approach, the optimal site‐specific solution was determined and constructed.…”

“…This was then assessed with field tracer testing to validate the findings. The full‐scale reconfiguration of the pond resulted in a measured increase in pond mean residence time of at least 20%; this increase occurred despite in situ sludge infill (for more detail: Coggins et al, ). The full‐scale trial not only validated the hydrodynamic modeling, but also, for the first time, demonstrated the success of hydraulic reconfiguration to improve pond hydraulics at the full‐scale.…”