Effects of groundwater abstraction and desalination brine deep injection on a coastal aquifer

Abstract

As a result of climate change, population increase and improvement of living standards, the water demand is annually growing drawing worldwide attention on seawater desalination to face water crisis. The total global desalination capacity is dominated by Reverse Osmosis (RO) and, often, this desalination process is fed with the brackish water extracted from coastal aquifers. After this process the desalted freshwater is obtained at a recovery factor of ca. 50%, while concentrate byproduct, named brine, is disposed back to coastal aquifers, seas, oceans or evaporative ponds, determining detrimental effects on the surrounding environment. A common approach to clean out the brine is the deep-well injection into coastal aquifers, exacerbating the seawater intrusion. The ultimate result is a reduction of the available water both in terms quantity and quality hampering the benefits of the desalination. The aim of this study is to investigate the effects of brine water injection in the Nile coastal aquifer, one of the largest underground freshwater reservoirs in the world, and to find a way to minimize and manage the environmental impact of the RO process. In order to simulate the effects of the brackish water extraction and the brine deep-injection on the Nile coastal aquifer, a combined seawater intrusion, numerical models for flow and salt transport model in aquifers and the solution-diffusion in RO practices were implemented. Different management scenarios were considered and their consequences on salt mass storage in the Nile coastal aquifer evaluated. According to the numerical results, the salinization of the coastal aquifer can be mitigated by reducing the concentration of the water feeding the reverse osmosis plant, i.e., mixing the extracted brackish water with a lower salinity water. Besides, low feed salinity leads to significant gains by decreasing the specific energy consumption of the desalination process.

Keywords: Brackish water extraction; Brine injection; Desalination; Reverse osmosis; Salt mass storage; Seawater intrusion.