Abstract
Traditionally, bathymetry mapping of ponds, lakes, and rivers have used techniques which are low in spatial resolution. Waste stabilisation ponds (WSPs) are utilised worldwide for wastewater treatment, and throughout their operation require periodic sludge surveys. Sludge accumulation in WSPs can impact performance by reducing the effective volume of the pond, and altering the pond hydraulics and wastewater treatment efficiency. Traditionally, sludge heights, and thus sludge volume, have been measured using techniques such as the 'sludge judge' and the 'white towel' test. Both of these methods have low spatial resolution, are subjective in terms of precision and accuracy, are labour intensive, and require a high level of safety precautions. A sonar device fitted to a remotely operated vehicle (ROV) can improve the resolution and accuracy of sludge height measurements, as well as reduce labour and safety requirements. This technology is readily available; however, despite its applicability, it has not been previously assessed for use on WSPs. This study aimed to design, build, and assess the performance of an ROV to measure sludge height in WSPs. Profiling of several WSPs has shown that the ROV with autonomous sonar device is capable of providing bathymetry with greatly increased spatial resolution in a greatly reduced profiling time. To date, the ROV has been applied on in excess of 400 WSPs across Australia, several large lakes, stormwater retention ponds, river beds, and drinking water reservoirs. ROVs, such as the one built in this study, will be useful for not only determining sludge profiles, but also in calculating sludge accumulation rates and in evaluating pond hydraulic efficiency. As demonstrated, this technology is not limited to application in wastewater management, with the potential for wider application in the monitoring of other small to medium sized water bodies, including reservoirs, lakes, channels, recreational water bodies, river beds, mine tailing dams and commercial ports.
Highlights
Bathymetry mapping of ponds, lakes, and rivers often use techniques which are low in spatial resolution, subjective in terms of precision and accuracy, labor intensive, and which require a high level of safety precaution
The main objective of this study was to assess the performance of a remotely operated vehicle (ROV) with GPS-equipped sonar to measure sludge height in a Waste stabilization ponds (WSPs), with the aim to develop it to a point where it could be implemented for research and within industry
Using Google Earth, the pond boundaries are defined by drawing a path around the perimeter; this path is saved as a Keyhole Markup Language (KML) file for input into the software
Summary
Bathymetry mapping of ponds, lakes, and rivers often use techniques which are low in spatial resolution, subjective in terms of precision and accuracy, labor intensive, and which require a high level of safety precaution. Sludge accumulation can lead to increased methane production, contributing to greenhouse gas emissions (Hernandez-Paniagua et al, 2014; Glaz et al, 2016) This knowledge is essential for planning pond maintenance, in particular sludge removal and disposal, which can be highly expensive and complex (Nelson et al, 2004; Picot et al, 2005; Alvarado et al, 2012a). Traditional methods of measuring sludge height, and total sludge volume, in WSPs include the use of a “sludge judge” (a clear plastic pipe) (Westerman et al, 2008), or the “white towel” test (Mara, 2004) Sludge surveys using these techniques are typically conducted on a rectangular grid, with height measurements taken by an operator deploying the measuring apparatus from a boat. Such surveys are time consuming and have low spatial resolution; data from these surveys is vital for sludge management (Peña et al, 2000; Nelson et al, 2004; Picot et al, 2005)
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