water Article The Cost of Brine Dilution in the Desalination Plants of Alicante Rubén Navarro 1 , Adoración Carratalá 2 and José Luis Sánchez Lizaso 3, *   Citation: Navarro, R.; Carratalá, A.; Sánchez Lizaso, J.L. The Cost of Brine Dilution in the Desalination Plants of Alicante. Water 2021, 13, 2386. https://doi.org/10.3390/w13172386 Academic Editor: Maurizio Barbieri Received: 12 July 2021 Accepted: 29 August 2021 Published: 30 August 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Mancomunidad de los Canales del Taibilla, Cartagena 30201, Colombia; ruben.navarro@mct.es 2 Departamento de Ingeniería Química, Universidad de Alicante, P.O. Box 99, 03080 Alicante, Spain; A.Carratala@ua.es 3 Departamento de Ciencias del Mar y Biología Aplicada, Universidad de Alicante, P.O. Box 99, 03080 Alicante, Spain * Correspondence: jl.sanchez@ua.es; Tel.: +34-590-3534 Abstract: To reduce the environmental impact of desalination plants, a good dilution of the brine is needed. Brine dilution may be carried out using diffusers, by mixing the concentrate with other effluents, or with seawater bypassing. Seawater bypassing increases the energy consumption of the plant but, thus far, this energy consumption has not been estimated. The environmental impact statement (EIS) of desalination plants in Alicante establishes a system of seawater bypassing for diluting brine and protecting the Posidonia oceanica seagrass meadows. The aim of this paper is to quantify the energy consumption of brine dilution, which was necessary for meeting the environmental requirements from 2012 to 2018. During the research period, the plants’ operation was variable, as it depended on the supply needs. The results indicate that the energy consumption of the dilution systems fluctuated between 2,135,315 kWh in 2012 and 685,988 kWh in 2013, with an average consumption of 1,205,952 kWh for the selected period. The energy cost in 2012 was EUR 179,556, while that for 2013 was EUR 60,787, with an average annual cost of EUR 91,690. This interannual variability is due to the difference in the production values of the plants and in the dilution ratio, which oscillated between 2.5 and 7.5 seawater:brine. In addition, the dilution showed an additional cost of the energy consumed by the desalination plants of around 1.7% on average. However, it also allowed the fulfillment of the established requirements in the EIS and the protection of the Posidonia oceanica seagrass from the discharge of the desalination plants. Keywords: brine dilution; energy cost; environmental protection; desalination discharges 1. Introduction One major concern regarding the development of seawater desalination is the im- pact of brine on the marine environment [1]. Concentrate discharge may affect sensitive species [2–5], thus reducing the biodiversity in marine environments [6–9]. It has been demonstrated that, in order to reduce or minimize these impacts, it is necessary to maxi- mize the mixing of brine with seawater [10,11]. The natural dispersion of effluent mainly depends on site-specific conditions—such as bathymetry (slope of the seafloor and water depth), geomorphology (bottom relief and roughness or rugosity), and hydrodynamics (waves, currents, and tides) [12,13])—but it also depends on the disposal methods, which may include the use of single or multiport diffusers [13,14]. In some cases, the salinity of the discharge may be reduced by mixing the brine with cooling water from a co-located power plant, or with treated wastewater effluent [15,16]. When these possibilities are not available, the mixing behavior can also be improved by bypassing seawater and mixing it with brine to reduce its salinity before its discharge to the marine environment [17]. In the Javea desalination plant (Alicante, Spain), a constant seawater-to-brine ratio of 4:1 is used to reduce the discharge salinity to below 44 psu, and a similar strategy is used for the Alcudia plant (Balearic Islands, Spain) [18–20]. Seawater bypassing increases the energy consumption of desalination plants; however, to this day, its energy consumption has not been quantified in detail. Only in the desalination plant of Javea, Sola et al. [20] indicate that the dilution system represents less than 3% of the cost of the plant’s energy consumption. Water 2021, 13, 2386. https://doi.org/10.3390/w13172386 https://www.mdpi.com/journal/water