1. Introduction
The continuous increase in global freshwater demand highlights the important role played by desalination to address water scarcity [
1]. In Latin America, climate change poses critical challenges, among which water scarcity is one of the most important [
2]. In Chile, which is highly affected by climate change [
3,
4], desalination of seawater using reverse osmosis has been proven to improve the social and economic sustainability of the country, because it can provide water for both human consumption and industrial activities. The industries in Chile, especially the copper and lithium mining industries, require very large quantities of water. In addition, Chile faces a critical challenge in providing water for the cities near to the Atacama Desert, which is considered the driest desert in the world. Owing to the geographic characteristics of Chile, with 6400 km of coastline and an average width of 180 km, seawater desalination is considered the best alternative to solve current and future challenges regarding water scarcity in the country [
5,
6].
The salinity of brine discharges from reverse osmosis plants is up to double that of seawater. In addition, they often contain chemicals used in the pretreatment and membrane cleaning processes. Some of these chemicals may be toxic to marine organisms [
7]. Brine tends to accumulate on the benthic area near the outfall, due to its high density with respect to seawater, and it then moves toward deeper waters following the bottom bathymetry [
8]. Therefore, it can induce stress responses in marine organisms, mainly benthic communities near the brine discharge [
7,
9,
10,
11,
12,
13]. Thus, these uncertainties regarding the environmental impacts of desalination on coastal systems represent a barrier to Chile’s water sustainability and socioeconomic development.
In Chile, the environmental impact assessment process is perceived as an important legal instrument to pursue environmental protection, sustainable development, and marine conservation [
14]. It is considered the most powerful management tool controlling environmental impacts from seawater reverse osmosis (SWRO) plants. However, normative and protocols related to SWRO plants are still under consideration. The environmental assessment process for the development of desalination plants in Chile began in 1997 through the Environmental Impact Evaluation System (
Servicio de Evaluación de Impacto Ambiental, SEIA). Desalination projects submitted to SEIA could be assessed in two types of environmental assessment regarding the characteristics of these projects, as their specific effects or circumstances. Thus, projects with less involvement are being assessed through the Environmental Impact Assessment (
Declaración de Impacto Ambiental, DIA), and projects with more involvement are being assessed through the Environmental Impact Study (
Estudio de Impacto Ambiental, EIA) [
14,
15]. In [
15], there are additional details about the environmental assessment process in Chile. Environmental monitoring plans (EMPs) ensure the effectiveness of the preventive and corrective measures established in DIAs or EIAs to protect marine environments [
16]. EMPs can identify potential negative environmental impacts of desalination discharges and mitigate them by adopting adequate measures [
11].
However, the weaknesses and gaps within the DIA or EIA frameworks must be fully understood and addressed. This study aims to assess the quality of EMPs and identify the process aspects that need improvement to achieve sustainable operation of desalination plants in Chile. This information can be used to conduct critical analyses to achieve the followings: (a) propose key environmental parameters that should be measured to identify the impacts of brine discharges, and (b) recognize the strengths and weaknesses within the current DIAs and EIAs frameworks in order to protect marine ecosystems from potential detrimental effects of the desalination industry.
2. Materials and Methods
A review of the DIAs and EIAs related to the construction and expansion of desalination projects in Chile was carried out based on the data compiled in the SEIA between 1997 and 2018 (
http://seia.sea.gob.cl). A total of 24 desalination projects were identified, with three SWRO plants (IDs: 1, 7, and 15 in
Table 1) that did not present EMPs for evaluation.
Figure 1 shows the location of the desalination projects identified. Therefore, 21 EMPs for discharging brine effluents from SWRO plants were evaluated.
The possible environmental impacts of each case were analyzed in order to perform adequate management of the brine discharges based on scientific criteria and achieve sufficient environmental protection. Thus, EMP requirements were specified according to the characteristics of the SWRO desalination plants and the marine ecosystem at the location of the brine effluent discharge.
The EMP requirements for monitoring the effects on marine ecosystems during the operation phase were identified. This approach also identifies the requirements for correct management of brine discharges [
17] and some considerations related to the characteristics related the Chilean environment for sustainable management of SWRO desalinations plants during the operation phase. The important requirements highlighted by this approach include: (i,ii) analysis of the composition of the effluent water and seawater is advisable to control the substances present in the effluents—in particular, those caused by the pretreatment or cleaning of membranes, such as coagulants, antifouling compounds, and nutrients; (iii) determination of the saline plume extension, because it can help in specifying the area potentially affected by the discharge; (iv) using salinity-sensitive species as bio-indicators, which was proven to be useful, because they can provide information on possible impacts on benthic habitats and allow a discrimination between the effects of desalination and other impacts that may coincide in space, such as the effects of sewage discharges; (v) analysis of the ecological and chemical qualities of the sediments in order to quantify the impact on the benthic in the discharge area; (vi) conducting a structural monitoring of the submerged outfall for the early detection of possible fractures and leaks; and (vii) implementing a contingency plan that includes mitigation measures to control and correct the identified detrimental effects in cases when negative effects on benthic communities, such as infauna or sensitive species, are evidenced [
8,
10,
11,
12,
16,
18].
Additional considerations were included in this approach to adopt it within the Chilean environmental legislation according to the specific characteristics of the Chilean environment and marine communities. Firstly, (viii) the potential effects of seawater intake on plankton communities were incorporated. The effects of the brine effluent on plankton communities is unknown; nevertheless, plankton cannot survive during the seawater intake [
12]. (ix) Moreover, toxicity testing is included in order to evaluate the effects of chemicals used in the pretreatment or membrane cleaning on the endemic species around the outfall area [
19]. Finally, no protected species, such as
P. oceanica in Spain or
P. australis in Australia, were identified in the outfall area; hence, the evaluation of how the effluents affect them was not considered a requirement in the EMPs [
13,
20].
The requirements extracted of each EMP were assessed using a semiquantitative scale (
Table 2) following the method proposed by [
17].
Finally, the quality of each EMP was estimated using Equation (1) as follows:
where
is the evaluation of requirements considered for managing desalination plants during the operation phase of each EMP
, and
is the necessary or unnecessary control parameters determined according to the characteristics of each desalination plant and the environment at the brine discharge location. The following parameters were considered according to these characteristics: the analysis of effluents and seawater quality (
), saline plume (
), analysis of sediment (
), use of bio-indicators
), structural monitoring of the submerged outfall
), existence of contingency plan (
), analysis of plankton communities in the seawater intake area
, and use of toxicological studies (
).
Furthermore, sampling designs of each EMP were evaluated. Sampling process design is defined according to the spatial and temporal variability to avoid pseudo-replication and allow the detection of significant differences among samples [
21,
22]. Therefore, the following requirements were considered important for an adequate sampling design: (i) the spatial–temporal characteristics of the sampling design; (ii) the correct description of the procedure to carry out the analysis of requirements; (iii) and the inclusion of before-after-control-impact (BACI) to understand the environmental impacts of SWRO desalination plants on marine ecosystems [
13].
In addition, irrelevant requirements were also evaluated. They are defined as those requirements that do not result in better control of the desalination plants during the operation phase and/or those with insignificant effects on the environment. These requirements are typically not based on scientific criteria and are not useful for managing SWRO plants during the operation phase [
17]. Finally, linear regressions were performed to assess the incorporation of EMP requirements, irrelevant parameters and sampling design requirements over time, and relationships between EMP requirements and the production capacity of SWRO plants. Significant levels were set at p < 0.05. R software was used to conduct statistical analyses and prepare graphs [
23].
4. Discussion
The analysis of projects submitted to SEIA provided a perspective of the brine production expected from the operative and projected SWRO plants in Chile. In the last decade, the production capacity of desalinated water in the country has notably increased, representing 77% of the total production of freshwater, and used for different applications [
25]. However, this significant development results in huge brine effluents delivered to the marine environment. Desalination is considered an important solution to solve the problem of water scarcity in Chile, especially for semiarid and arid areas (Central and Northern Chile). Moreover, 68% of the total production capacity evaluated is aimed at the industrial sector. However, there has been a marked increase in the production of desalinated water for the public sector since 2012. Water supplies in the semiarid and arid zones are intensified by the huge freshwater demand for industrial applications, especially in the mining industry [
25]. Moreover, the number of desalination projects is expected to increase toward the south as a result of the accompanied climate change-driven displacement of the Atacama Desert [
2]. The investigations conducted in this study demonstrate that about 88% of the projects in the Antofagasta and Atacama Regions have been submitted to SEIA, which include those approved or currently subjected to evaluation.
This increase in desalinated water production may cause negative impacts on the marine ecosystems with incorrect environmental management of the SWRO plants operation as a result of the brine discharges [
12,
13]. The results show that the brine discharge production in Chile was about 1.6 Mm
3/day from all desalination projects currently operating or under the SEIA consideration. Thus, there is an urgent need for correct implementation of EMPs for desalination projects in order to ensure the environmental protection of the locations, where the currently operating plants discharge their effluents, facilitate the installation of new SWRO projects, and increase their economic viability through only focusing on the parameters that are environmentally relevant.
The significant increasing trend in the control requirements within EMPs over time in all 21 EMPs evaluated reflects an awareness of the local authorities (led by the Ministry of the Environment of Chile) to solve the water scarcity crises through environmentally sustainable practices. However, environmentally relevant parameters in current EMPs reached only 48.6% of the total requirements. Thus, improvements, especially related to monitoring the seawater and brine qualities by including biological tools for environmental diagnosis, are necessary (e.g., assessment of bio-indicators, biomarkers, and/or stress responses) using local species; contingency plans to apply mitigation measures when environmental impacts are identified; and frequent outfall inspection for the early detection of possible leaks or fractures. These are highlighted as the main considerations for future EMPs, because they are only considered in 50% of the current EMPs.
Similar results were obtained in the study conducted by [
17], which showed a significant trend in improving the environmental requirements and sampling designs in Spain’s EMPs; however, the majority of EMPs in Spain displayed less appropriate sampling designs compared to the Chilean EMPs. A good sampling design allows better detection of potential negative effects on the marine environment, so that they can be mitigated and controlled [
11]. To address the latter, it is essential to increase spatial/temporal variabilities in the environmental requirements of the assessment conducted in the affected area of the brine discharge and in control locations [
13].
Although DIA is a relative brief procedure compared with EIA [
14], no significant differences were found between them in the period of evaluation or in requirements included in EMPs for desalination projects analyzed.
A number of disadvantages have been identified in the assessment of EMPs in Chile. For instance, no relation was found between the environmental requirements and the increase in the brine discharge from SWRO plants. However, an increase in the brine production may lead to creation of saline plumes and an increase in the affected area [
8]. Similarly, an increase in the freshwater production is related to an increase in the seawater intake capacity, which could affect the surrounding plankton communities [
12]. On the other hand, the irrelevant parameters (77.4% of the total) are better suited to other types of effluents, such as sewage and wastewaters from agriculture [
26], but not from the SWRO plant operation.
In terms of biomonitoring, it is important to adopt requirements that focus on species with high probability of occurrence in the affected area. SWRO plants evaluated in this study use submerged outfalls as discharge method; thus, monitoring the intertidal and littoral communities, which are unlikely to be affected, has little value to the environmental diagnosis [
8,
27]. Including these irrelevant parameters in the assessment increases the cost of EMPs and does not offer valuable information.
There are a lot of relevant studies in the literature documenting impacts from desalination discharges. However, the available published information is of little use in the evaluation of impacts on Chilean coastal systems. Model species, for which impacts are examined in these studies, have a completely different ecological structure and potential tolerance thresholds compared to the marine communities of the Humboldt system dominant in the Chilean coastline. Therefore, it is difficult to envision recommendations for sustainable and biologically nonthreatening operation to be incorporated in the EMPs, due to the absence of toxicological assessments on local species and communities. Considering that only 28.5% of the EMPs assessed implement these analyses, further investigations are required to generate basic information on biological effects of brines on Chilean coastal communities, which are valuable information for the development of up-to-date biomonitoring protocols to achieve accurate and reliable environmental diagnosis. These actions are essential to keep up with the fast growth of the SWRO industry in Chile that is expected to further increase due to climate change. However, according to the international experience in Spain and Australia, negative impacts of SWRO discharges on the marine environment caused by the development in desalination sector can be efficiently mitigated [
9,
11,
12,
28,
29].
Research has proven that marine macrophytes are a suitable species for biomonitoring that can reflect the impacts of the desalination industry—for example, marine angiosperms including
Posidonia oceanica found in the Mediterranean Sea [
20,
30,
31] or
Posidonia australis found in Australia [
32]. In addition, the authors of [
17] showed that areas with protected species, such as
P. oceanica, indicated greater environmental requirements in their EMPs for monitoring the effect of brine effluents on marine ecosystems. This, added to their ecological relevance as a base of trophic networks, suggests that macroalgae and kelp forests, since they are dominant in Chilean coastal ecosystems, would make good candidates for future eco-toxicological assessments regarding brine discharge impacts in Chile [
33].