Improved understanding of dense jet dynamics to guide management of desalination outfalls

With the growing adoption of Seawater Reverse Osmosis desalination technologies, there is a concurrent increase in the production of dense, hypersaline by-products. To minimize environmental impact to benthic biota, these wastes are commonly disposed via submerged diffuser systems in dynamic coastal environments. Traditional diffuser design approaches have relied on empirical techniques derived from small-scale laboratory experiments. This approach has provided a sound basis for preliminary design and regulatory approval of these systems. In practice the coastal receiving environment differs from the idealistic laboratory environments from which empirical scaling functions were derived. With the recent advances in computational power and development of computational fluid dynamics (CFD) approaches, it is now feasible to utilize CFD-based analysis to examine the dynamics of dense brine plumes under conditions representative of in-situ field practices. For the first time, this study details a high-resolution three-dimensional laboratory-scale numerical simulation of an inclined dense jet diffuser subject to ambient crossflow. The quasi-steady CFD simulations were performed using the Reynolds averaged Navier-Stokes equations with a k-ω shear stress transport turbulence closure scheme. The study compliments existing laboratory studies by assessing CFD simulation results against empirical scaling approaches. Quantitative assessment of diffuser performance with regard to trajectory and dilution for an array of dynamic-crossflow based regimes is presented. Results show strong agreement with existing small-scale laboratory experiments, with significant potential for upscaling to field-scale applications. Simulated dynamic ambient regimes show the influence of crossflow upon jet trajectory, dilution and lower boundary concentration is significant. The effect of flow structure and the subsequent influence on jet dynamics is discussed. This model poses as an effective strategy for future design of brine outfall systems, with strong potential for application in water quality management for both plant operators and regulators.