Desalination Brine Mining Challenge

By Mr. Pedro Almagro, General Manager, Lantania Desalination

The shortage of water supplies for drinking and irrigation purposes has intensified the use of non-conventional technologies like seawater (SW) and brackish water (BW) desalination.

Today, reverse osmosis (RO) is the leading technology for new desalination installations, with a 77% share in world desalting production capacity and an 88% share in over 20,000 desalination plants installed worldwide, and this technology continues to grow. In fact, in recent years, numerous large-scale desalination projects (over 250 MLD) have been launched despite the COVID-19 impediment. The Middle East has become the leader in mega seawater desalination plants. The trend in North Africa is similar, considering water shortage in countries like Algeria, Morocco, Libya, and Egypt.

And at this point arises a two customary questions which have always worried scientists: what should be done with the brine rejection? How can we manage it?

Brine disposal is generally deeply evaluated in the preliminary studies of each project, by developing environmental impact assessment (EIA) studies to determine the best location for the discharge to minimize any significant impact on the receiving environment. Currently, there are no worldwide standards that specifically apply to seawater-generated brines, and sometimes the Tenders set the discharge thresholds, for each specific project, regarding parameters like salinity, turbidity, temperature, and some dissolved chemicals.

So far, the most common practice for brine disposal consists in assuring a good dispersion of the residual brines using several diffusers in the outfall. Nevertheless, taking into account the substantial number of desalination plants installed worldwide and their increased capacity, experts, researchers, technological platforms, and companies with a large track record in the field of desalination are looking for viable alternatives to make desalination more sustainable, while taking advantage of the economic potential of the generates brines/ valuable products contained in this brine effluent. In this sense, the IDA, SWCC and DTRI are making notable efforts to explore desalination brine mining opportunities.

The common concepts considered for brine management cases are focussed on 1) limiting or avoiding brine discharge by introducing substantial changes in the process with the aim to reach zero liquid discharge (ZLD) or near ZLD and on 2) brine mining or brine valorisation.

The first approach, usually based on thermal processes to reach ZLD, generally requires high investment. This way would make sense for effluents from brackish water desalination plants but could not be applied, especially in the near future for seawater desalination, mainly because of the techno-economical barrier.

Nevertheless, the most promising alternative is brine mining, which consists in internal valorisation (brine reuse in the desalination plant), and/or external valorisation (brine conditioning for other industries).

Considering the physicochemical properties of the generated brines, this concentrate can be used for direct or indirect recovery of valuable byproducts. Various types of salts and especially magnesium and bromine could be recovered in a selective way. Many approaches are aligned with this route by trying to reduce the volume of the Reverse Osmosis (RO) concentrate by implementing hybrid membrane configurations and/or high recovery RO and to improve the quality of the water produced using minerals from the generated brine.

Recent strategic lines for brine management are focused on brine conditioning for other industries and especially for the chloralkali industry. In terms of energy, producing the brine for the chloralkali industry, starting from a RO concentrate, requires less energy to concentrate NaCl than starting from seawater. However, the presence of high content of divalent ions in the RO brine requests investment in capex and opex, which are not economically attractive, considering the low price of the sodium chloride.

When it comes to brines from inland desalination plants, the salinity is a serious and significant environmental problem and the legislation is more stringent with these saline effluents. Disposal costs for inland desalination plants are even higher than those for plants discharging brine into the sea. Some of the options for brine disposal from inland desalination plants are deep well injection, evaporation ponds, discharge into surface water bodies, disposal to municipal sewers, concentration into solid salts and irrigation of plants tolerant to high salinity.

Recent strategic business lines for brine management focus on the accomplishment of the ZLD concept and the recovery of valuable byproducts through the combination of different technologies (i.e. hybrid systems), while trying to make the desalination process environmentally more sustainable. One of the biggest challenges is to develop innovative brine management alternatives combining low energy consumption and competitive extraction of minerals from high saline effluents.

About the Author

Pedro Almagro has over 20 years’ experience in the water business and nowadays is General Manager in Lantania Desalination.

Pedro has been Abengoa Agua’s CEO over the past 5 years. In this period, he leaded the award and execution of some of the world's largest desalination plants, doubling the desalination contracted capacity of the company.

Industrial Technical Engineer by profession, he started in the water sector in 1998 as a proposal engineer developing his career lately in different positions as International Proposal Department Manager, China′s Country Manager and USA General Director.?