Hydrodynamic behaviour of desalination brine discharges in the marine environment

Abstract

Brine is a dense effluent sourced from desalination plants that produce drinking and industrial water by seperating salt content of seawater or groundwater. Discharge of brine to the surface waters via outfalls is the most common method of brine disposal because of generally being the most feasible method. In this study, hydrodynamic behaviour of brine discharges under regular wave effect was analysed experimentally in three different configurations. In the first part of the experimental study, mixing of a stagnant salt layer with the effect of waves was considered. Measured vertical salinity profiles and calculations showed that the external wave energy added to the water column caused rising of potential energy which was observed in the form of thicker salt layers. In the second part of the experimental study, a single port, horizontal brine discharge was taken into consideration. It was determined that the wave motion cause oscillation of discharged jet and shifted its impingement point to the bottom compared to stagnant ambient water. It was determined that discharge direction to wave propagation is an important parameter which effects shape, thickness and propagation speed. In the third part of the experimental study, inclined dense jet (45° ve 60° ) discharge was analysed under regular wave conditions. It was determined that wave motion affects terminal rise height and impingement point of dense jets. In addition, propagation rate of dense layer in transitional zone was under the effect of wave motion. It was determined that the wave motion contributed to the propagation with its horizontal velocity component. The results for stagnant ambient were confirmed this finding, too. In addition to experimental studies, widely used entrainment models (CORMIX, UM3 and JETLAG) for brine discharges evaluated in the context of multiport brine discharges. It was determined that, mentioned models give meaningful results in the case of not merging jets with large port spaces between them. Otherwise, they are not compatible with experimental data. Lastly, two simple programmes, that roughly simulate density current spreading, were developped as a pre-design tool.