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

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Abstract Waste stabilization ponds (WSPs) are used extensively for the treatment of wastewater in Australia, mostly in regional and remote areas. Wastewater treatment plants (WWTPs) using pond technologies are also distributed over the full geographical extent of Australia, encompassing many climatic zones. Predominantly used to service small to medium‐sized communities, WSPs are also used to service large metropolitan Australian populations, up to 2.5 million people. When well‐maintained, WSPs are a sustainable and resilient treatment option, and treatment is achieved at significantly lower cost when compared with conventional WWTPs. Increasing population, changing regulations, and climate variability are placing increasing pressure on Australian WSP systems. Sludge accumulation over time presents a significant challenge to pond maintenance, along with increasing occurrence of toxic cyanobacterial bloom events. These challenges are only enhanced by the wide geographical distribution and by increasing operational and maintenance costs. Increased demand for recycled water is placing further pressure on Australian WSP systems, as higher value treated water is expected from WSP infrastructure that is often overloaded or under‐designed. This increased demand for high‐quality treatment presents an opportunity for operators and researchers to develop a better understanding of the coupling between hydraulics and microbial ecology of these systems. With more stringent guidelines for greenhouse gas emissions (GHGs), a better understanding of biophysicochemical processes in WSPs will lead to better estimates of GHG fluxes and variability. This information will become critical for the future planning, maintenance and operation of WSPs, and will result in a better understanding of WSP systems overall. This article is categorized under: Engineering Water > Water, Health, and Sanitation Engineering Water > Sustainable Engineering of Water
Geographic distribution of the 1,234 Australian wastewater treatment plants (WWTPs), with 60% (737) having predominately pond based treatment (blue), and 77% (943) using pond technology as part of the treatment process (blue and green) (data source: Hill et al., ); Köppen‐Geiger climate zones are overlaid. Ponds were visually classified from aerial photos; plants classified as pond dominant have >75% of their treatment in ponds, while WWTPs including ponds had 50‐75% of their treatment in ponds
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Conceptual model of processes, drivers, and criteria for current and proposed future design of waste stabilization ponds (WSPs). This also shows that the relationships between the main drivers are complex, as sludge has an effect on hydraulics, and hydraulics interacts with pond ecology
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A schematic showing the key biogeochemical process responsible for the treatment process in waste stabilization ponds (WSPs), but also supporting ecosystem function. The strong relationship between hydraulic and biological/chemical process is considered key in the performance of WSPs
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A schematic illustration of greenhouse gas (GHG) cycling and emission pathways in waste stabilization ponds (WSPs). The most prevalent emission pathways are turbulence‐driven diffusive flux micro‐ and macro‐ebullition. Meteorological and wind forcings are important drivers of the processes occurring in‐pond; in particular, the occurrence of diurnal stratification can have a significant effect on GHG emission from ponds. The relative contribution of each process can vary significantly not only between systems, but also spatially within the same system. Plant mediated transport is less relevant in WSPs, as vegetation growth on banks is actively suppressed at the majority of Australian WSPs, but shown here as one of the possible GHG pathways
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Cyanobacterial and cyanotoxins occurrence and risk assessment in waste stabilization ponds in Western Australia. Reuse water from waste stabilization ponds (WSPs) was classified into four groups with respect to maximum cyanobacterial biomass: From low (I; green), medium (II; blue‐green), high (III; orange) to very high (IV; red). Red crosses indicate maximum microcystin (MC) concentrations found in the reuse samples with +++ being >20 μg MC L−1, ++ being 4–20 μg MC L−1, and + being >0–4 μg MC L−1. No microcystins were found in sites not marked by red crosses. Please note that cyanobacterial biomass is on a logarithmic scale. WSPs in this case study were divided into three categories requiring different monitoring frequencies, with a requirement for very regular monitoring in the red category as established by a recently developed risk assessment framework (Barrington, Ghadouani, Sinang, & Ivey, ; Reichwaldt et al., )
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Examples of waste stabilization pond systems from regional Western Australia (a, b), showing normal operating conditions (c) and one experiencing a spectacular outbreak of cyanobacterial blooms in warmer months, potentially leading to significant shading of the water column (d)
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Traditional sludge profiling with sludge judge (a), a remote‐controlled boat fitted with GPS‐equipped sonar for sludge bathymetry mapping (b), an example two‐dimensional contour of a profiled pond (c), and the GPS survey track over a pond (d)
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An example of a non‐uniform sludge distribution (displayed as sludge height in meters) in a Western Australian waste stabilization pond (WSP), where a preferential flow path has resulted in a channel and basin formation and undesirable hydraulic performance (i.e., short‐circuiting of flow and reduced mean hydraulic residence time)
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Melbourne Water's Western treatment plant (a), situated in Werribee, Victoria, was established in 1897 and occupies a site of more than 10,000 ha (b). This is one of the largest wastewater treatment plants using waste stabilization pond treatment in the world, servicing up to 58% of Melbourne's 5 million residents and producing up to 40 billion liters of recycled water each year. The ponds and wetlands on the site are considered of international significance, with more than 280 bird species recorded on the site, and are protected under the Ramsar convention. Source: Images courtesy of Melbourne Water
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Engineering Water > Sustainable Engineering of Water

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