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Waste stabilisation ponds (WSP) are designed to treat wastewater through natural microbiological, photosynthetic, biochemical, physico-chemical and hydrodynamic processes. They are used throughout the world for wastewater treatment due to their minimal technical requirements, low cost and minimal energy consumption. It is well recognised that WSP hydrodynamics plays a crucial role influencing WSP treatment efficiency. In this study, published WSP literature is reviewed with a focus on the importance of environmental forces, pond configurations and pond loadings on WSP hydrodynamics and pond treatment efficiency. The findings are used to propose future WSP design and modelling requirements. It has been found that the interrelated effects of multiple factors such as pond length-to-width ratio, inlet/outlet configuration, temperature, solar radiation and wind on WSP treatment performance are not investigated sufficiently at present. It is suggested that a system based on numerical pond modelling and field measuring analyses be formulated to address the interacting influences of these factors on WSPs. Consequently, field studies on full-scale WSPs are required to obtain a complete dataset for validation purposes. In this regard, a combination of three-dimensional pond water temperature survey and tracer concentration mapping is suggested. Details of specific modelling components, such as sludge accumulation, turbulence mechanisms and the assumption of constant influent conditions, require further attention. As a result of this review process, a strategic evaluation framework together with the required dataset for the modelling and field work activities are proposed. This paves the way for subsequent studies on WSP hydrodynamics and treatment efficiency, thus benefitting pond design and operation processes. [ABSTRACT FROM AUTHOR]

There is a widespread need for the use of quantitative microbial risk assessment (QMRA) to determine reclaimed water quality for specific uses, however neither faecal indicator levels nor pathogen concentrations alone are adequate for assessing exposure health risk. The aim of this study was to build a conceptual model representing factors contributing to the microbiological health risks of reusing water treated in maturation ponds. This paper describes the development of an unparameterised model that provides a visual representation of theoretical constructs and variables of interest. Information was collected from the peer-reviewed literature and through consultation with experts from regulatory authorities and academic disciplines. In this paper we explore how, considering microbial risk as a modular system, following the QMRA framework enables incorporation of the many factors influencing human exposure and dose response, to better characterise likely human health impacts. By using and expanding upon the QMRA framework we deliver new insights into this important field of environmental exposures. We present a conceptual model of health risk of microbial exposure which can be used for maturation ponds and, more importantly, as a generic tool to assess health risk in diverse wastewater reuse scenarios. [ABSTRACT FROM AUTHOR]

Sunlight disinfection is important for treatment of wastewater within maturation ponds. This study analyses the movement of Escherichi coli within a slice of a maturation pond, being affected by stratification, sunlight attenuation and mixing driven by wind shear and natural convection using computational fluid dynamics (CFD). Since the exposure to ultraviolet light is most effective in the near-surface region of the pond, natural convective mixing mechanisms to transport the pathogens from the lower parts of the pond are critical for disinfection efficacy. Different turbulence models are considered for closure of the momentum conservation equations and compared with a laminar flow simulation and a completely stirred tank reactor (CSTR) model. The effect of turbulence and stratification is shown to be significant for thermal and velocity distributions, and predictions of E. coli die-off. Greater volume-averaged E. coli die-off was predicted by the computationally convenient CSTR model than the CFD turbulence and laminar models. The simulation results are compared with experimental data and show that complete vertical mixing occurs in a diurnal pattern aiding die-off in sunlight-attenuating water. Practical applications of the model can assist in management strategies for maturation ponds such as off-take locations/times and evaluating seasonal variations in sunlight disinfection. • A CFD model of the die-off of E. coli within a maturation pond is presented. • The model includes natural convective mixing and sunlight attenuation. • Complete vertical mixing occurs in a diurnal pattern consistent with field measurements. • Turbulence and stratification significantly influence E. coli die-off via sunlight disinfection. • The model has value for aiding pond design and operational management. [ABSTRACT FROM AUTHOR]