Abstract
Brine discharges from desalination plants into low-flushing water bodies are challenging from the point of view of dilution, because of the possibility of background buildup effects that decrease the overall achievable dilution. To illustrate the background buildup effect, this paper uses the Arabian (Persian) Gulf, a shallow, reverse tidal estuary with only one outlet available for exchange flow. While desalination does not significantly affect the long-term average Gulf-wide salinity, due to the mitigating effect of the Indian Ocean Surface Water inflow, its resulting elevated salinities, as well as elevated concentrations of possible contaminants (such as heavy metals and organophosphates), can affect marine environments on a local and regional scale. To analyze the potential effect of background salinity buildup on dilutions achievable from discharge locations in the northern Gulf, a 3-dimensional hydrodynamic model (Delft3D) was used to simulate brine discharges from a single hypothetical source location along the Kuwaiti shoreline, about 900 km from the Strait of Hormuz. Using nested grids with a horizontal resolution, comparable to a local tidal excursion (250 m), far field dilutions of about 28 were computed for this discharge location. With this far field dilution, to achieve a total dilution of 20, the near field dilution (achievable using a submerged diffuser) would need to be increased to approximately 70. Conversely, the background build-up means that a near field dilution of 20 yields a total dilution of only about 12.
Highlights
Marine impacts associated with brine discharge are mainly judged on their brine and contaminant concentrations after initial mixing
The primary objective of this paper is to investigate the potential background buildup of a low-flushing water body on a local scale
This paper used a 3-dimensional finite difference hydrodynamic model, coupled with a water quality module (Delft3D-FLOW) [25,26], as a tool to determine the far field dilution of various quality module (Delft3D-FLOW) [25,26], as a tool to determine the far field dilution of various contaminants, as well as to quantify a background far field concentration that may affect near field contaminants, as well as to quantify a background far field concentration that may affect near field outfalls
Summary
Marine impacts associated with brine discharge are mainly judged on their brine and contaminant concentrations after initial mixing (dilution). The effectiveness of any discharge design will depend on the relative magnitude of the near and far field dilution. The near field is facilitated by turbulent entrainment processes, while the far field is dominated by advection and diffusion processes. The far field dilution is defined as: SF = (co − ca )/(cF − ca ), (1). Where co , ca , and cF are the pollutant concentrations in the discharge, the ambient (water not influenced by the discharge) and the far field (region >~100 meters surrounding the discharge), and the near field dilution is defined as: SN = (co − cF )/(cN − cF ), (2). Where cN is the concentration in the near field (
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