Effects of desalination brine and seawater with the same elevated salinity on growth, physiology and seedling development of the seagrass Posidonia australis

The evolutive role of shoot apical meristems in the adaptation of angiosperms to life at sea and the jump to potential environmental biotechnology applications

Seagrasses have adapted to a submerged lifestyle in seawater through a complex set of evolutionary processes. However, they show sensitivity to increases in natural salinity levels such as those commonly found in discharges of desalination plants, which have exponentially grown due to water scarcity in highly populated temperate areas, such as the Mediterranean basin. This study assessed the effects of brine-derived hypersalinity on the Mediterranean seagrass Posidonia oceanica, focusing on the metabolic responses of shoot apical meristems (SAMs). Although most physiological and genetic studies have used leaves, SAMs are more directly correlated with plant survival and might be more responsive to salinity stress. The experiments were: a controlled mesocosm of more than six practical salinity units (psu) over natural levels using either artificial salts or desalination brine and field transplantation experiments comparing two sites following the dilution plume of the brine (+5 and + 2 psu) with control. Hydrogen peroxide (H2O2), thiobarbituric acid reactive substances (TBARS), and ascorbate were measured to determine oxidative stress and damage, as well as relative expression of genes related to osmotic regulation and oxidative responses. Overall, relative expression of genes related to osmotic regulation (SOS1, SOS3, AKT 2/3) and oxidative stress (STRK1, CAT, MnSOD, FeSOD, APX, GR) was higher in SAMs at higher brine exposures, indicating a more active metabolic response in this organ. Similarly, reactive oxygen species (ROS) production and lipid peroxidation were higher closer to brine discharge and total ascorbate lower, indicating a correlative response with stressor intensity. These findings confirm that SAMs play an essential role in P. oceanica hypersalinity responses and its adaptation to life in the marine environment. Finally, the use of P. oceanica SAMs in this study is highly recommended for an early detection of threats caused by desalination brines that may cause physiological damage and meadow regression.

Acidification alleviates the inhibition of hyposaline stress on physiological performance of tropical seagrass Thalassia hemprichii

Since the Industrial Revolution, increasing atmospheric CO2 concentrations have had a substantial negative impact influence on coastal ecosystems because of direct effects including ocean acidification and indirect effects such as extreme rainfall events. Using a two-factor crossover indoor simulation experiment, this study examined the combined effects of acidification and hyposaline stress on Thalassia hemprichii. Seawater acidification increased the photosynthetic pigment content of T. hemprichii leaves and promoted seagrass growth rate. Hyposaline stress slowed down seagrass growth and had an impact on the osmotic potential and osmoregulatory substance content of seagrass leaves. Acidification and salinity reduction had significant interaction effects on the photosynthesis rate, photosynthetic pigment content, chlorophyll fluorescence parameters, and osmotic potential of T. hemprichii, but not on the growth rate. Overall, these findings have shown that the hyposaline stress inhibitory effect on the T. hemprichii physiological performance and growth may be reduced by acidification.

Impacts of Desalination Brine Discharge on Benthic Ecosystems

Seawater reverse osmosis (SWRO) desalination facilities produce freshwater and, at the same time, discharge hypersaline brine that often includes various chemical additives such as antiscalants and coagulants. This dense brine can sink to the sea bottom and creep over the seabed, reaching up to 5 km from the discharge point. Previous reviews have discussed the effects of SWRO desalination brine on various marine ecosystems, yet little attention has been paid to the impacts on benthic habitats. This review comprehensibly discusses the effects of SWRO brine discharge on marine benthic fauna and flora. We review previous studies that indicated a suite of impacts by SWRO brine on benthic organisms, including bacteria, seagrasses, polychaetes, and corals. The effects within the discharge mixing zones range from impaired activities and morphological deformations to changes in the community composition. Recent modeling work demonstrated that brine could spread over the seabed, beyond the mixing zone, for up to several tens of kilometers and impair nutrient fluxes from the sediment to the water column. We also provide a possible perspective on brine's impact on the biogeochemical process within the mixing zone subsurface. Desalination brine can infiltrate into the sandy bottom around the discharge area due to gravity currents. Accumulation of brine and associated chemical additives, such as polyphosphonate-based antiscalants and ferric-based coagulants in the porewater, may change the redox zones and, hence, impact biogeochemical processes in sediments. With the demand for drinking water escalating worldwide, the volumes of brine discharge are predicted to triple during the current century. Future efforts should focus on the development and operation of viable technologies to minimize the volumes of brine discharged into marine environments, along with a change to environmentally friendly additives. However, the application of these technologies should be partly subsidized by governmental stakeholders to safeguard coastal ecosystems around desalination facilities.

Transcriptomic profiles and diagnostic biomarkers in the Mediterranean seagrasses Posidonia oceanica and Cymodocea nodosa reveal mechanistic insights of adaptative strategies upon desalination brine stress

Seawater desalination by reverse osmosis is growing exponentially due to water scarcity. Byproducts of this process (e.g. brines), are generally discharged directly into the coastal ecosystem, causing detrimental effects, on benthic organisms. Understanding the cellular stress response of these organisms (biomarkers), could be crucial for establishing appropriate salinity thresholds for discharged brines. Early stress biomarkers can serve as valuable tools for monitoring the health status of brine-impacted organisms, enabling the prediction of long-term irreversible damage caused by the desalination industry. In this study, we conducted laboratory-controlled experiments to assess cellular and molecular biomarkers against brine exposure in two salinity-sensitive Mediterranean seagrasses: Posidonia oceanica and Cymodocea nodosa. Treatments involved exposure to 39, 41, and 43 psu, for 6 h and 7 days. Results indicated that photosynthetic performance remained unaffected across all treatments. However, under 43 psu, P. oceanica and C. nodosa exhibited lipid oxidative damage, which occurred earlier in P. oceanica. Additionally, P. oceanica displayed an antioxidant response at higher salinities by accumulating phenolic compounds within 6 h and ascorbate within 7 d; whereas for C. nodosa the predominant antioxidant mechanisms were phenolic compounds accumulation and total radical scavenging activity, which was evident after 7 d of brines exposure. Finally, transcriptomic analyses in P. oceanica exposed to 43 psu for 7 days revealed a poor up-regulation of genes associated with brassinosteroid response and abiotic stress response, while a high down-regulation of genes related to primary metabolism was detected. In C. nodosa, up-regulated genes were involved in DNA repair, cell cycle regulation, and reproduction, while down-regulated genes were mainly associated with photosynthesis and ribosome assembly. Overall, these findings suggest that 43 psu is a critical salinity-damage threshold for both seagrasses; and despite the moderate overexpression of several transcripts that could confer salt tolerance, genes involved in essential biological processes were severely downregulated.

Ecocriminological analysis of brine in aquatic ecosystems: impacts on Posidonia oceanica and the search for restorative justice solutions

The consumption of fresh water has generated additional problems in certain territories, along with the consequences of global warming. This has meant that in the most vulnerable areas, such as the Balearic archipelago in the Mediterranean, alternative water supply systems have been established: desalination plants. However, the ecological impact of these infrastructures is great, mainly affecting aquatic ecosystems. In light of the above, this paper addresses the ecological harm caused by desalination and brine discharges on a protected and priority species, P. Oceanica. Taking as ethico-legal foundation the theory of ecological justice, a multilevel analysis was carried out from an ecocriminology perspective on the impacts of this authorized practice on P. Oceanica and other species. Finally, a restorative justice view will allow us to understand and envision possible solutions to this ecological harm.

Desalination brine effects beyond excess salinity: Unravelling specific stress signaling and tolerance responses in the seagrass Posidonia oceanica

Desalination has been proposed as a global strategy for tackling freshwater shortage in the climate change era. However, there is a concern regarding the environmental effects of high salinity brines discharged from desalination plants on benthic communities. In this context, seagrasses such as the Mediterranean endemic and ecologically important Posidonia oceanica have shown high vulnerability to elevated salinities. Most ecotoxicological studies regarding desalination effects are based on salinity increments using artificial sea salts, although it has been postulated that certain additives within the industrial process of desalination may exacerbate a negative impact beyond just the increased salinities of the brine. To assess the potential effect of whole effluent brines on P. oceanica, mesocosm experiments were conducted within 10 days, simulating salinity increment with either artificial sea salts or brines from a desalination plant (at 43 psμ, 6 psμ over the natural 37 psμ). Morphometrical (growth and necrosis), photochemical (PSII chlorophyll a fluorometry), metabolic, such as hydrogen peroxide (H2O2), thiobarbituric reactive substances (TBARS) and ascorbate/dehydroascorbate (ASC/DHA), and molecular (expression of key tolerance genes) responses were analyzed in each different treatment. Although with a still positive leaf growth, associated parameters decreased similarly for both artificial sea salt and brine treatments. Photochemical parameters did not show general patterns, although only P. oceanica under brines demonstrated greater energy release through heat (NPQ). Lipid peroxidation and upregulation of genes related to oxidative stress (GR, MnSOD, and FeSOD) or ion exclusion (SOS3 and AKT2/3) were similarly incremented on both hypersalinity treatments. Conversely, the ASC/DHA ratio was significantly lower, and the expression of SOS1, CAT, and STRK1 was increased under brine influence. This study revealed that although metabolic and photochemical differences occurred under both hypersalinity treatments, growth (the last sign of physiological detriment) was similarly compromised, suggesting that the potential effects of desalination are mainly caused by brine-associated salinities and are not particularly related to other industrial additives.

Advances in understanding multilevel responses of seagrasses to hypersalinity

Human- and nature-induced hypersaline conditions in coastal systems can lead to profound alterations of the structure and vitality of seagrass meadows and their socio-ecological benefits. In the last two decades, recent research efforts (>50 publications) have contributed significantly to unravel the physiological basis underlying the seagrass-hypersalinity interactions, although most (∼70%) are limited to few species (e.g. Posidonia oceanica, Zostera marina, Thalassia testudinum, Cymodocea nodosa). Variables related to photosynthesis and carbon metabolism are among the most prevalent in the literature, although other key metabolic processes such as plant water relations and responses at molecular (i.e. gene expression) and ultrastructure level are attracting attention. This review emphasises all these latest insights, offering an integrative perspective on the interplay among biological responses across different functional levels (from molecular to clonal structure), and their interaction with biotic/abiotic factors including those related to climate change. Other issues such as the role of salinity in driving the evolutionary trajectory of seagrasses, their acclimation mechanisms to withstand salinity increases or even the adaptive properties of populations that have historically lived under hypersaline conditions are also included. The pivotal role of the costs and limits of phenotypic plasticity in the successful acclimation of marine plants to hypersalinity is also discussed. Finally, some lines of research are proposed to fill the remaining knowledge gaps.

The influence of decreased salinity levels on the survival, growth and physiology of eelgrass Zostera marina

Low salinity generally promotes the growth and propagation of temperate seagrasses, but the appropriate range is unclear. We subjected shoots of eelgrass Zostera marina to different salinity levels [10, 15, 20, 25, 30 PSU (control)] for 6 weeks under controlled laboratory conditions. We measured eelgrass responses in terms of survivorship, growth, productivity, leaf pigmentation and carbohydrate concentrations. Survival analysis combined with growth assessment suggested that the optimal salinity range for the propagation of Z. marina shoots was 18-21 PSU. Structural equation model (SEM) analysis indicated that the promotion effect of decreased salinity levels on the survival and growth of Z. marina shoots mainly depended on the increase in chlorophyll content and the accumulation and synthesis of nonstructural carbohydrates. The carotenoid content and soluble sugar content of the aboveground tissues of Z. marina shoots exposed to 20 PSU were 1.1 and 1.6 times higher than those of shoots under the control, respectively. The results will provide valuable data that could prove helpful in the development of efficient artificial propagation technology for Z. marina shoots.

Burt J. Long-term, basin-scale salinity impacts from desalination in the Arabian/Persian Gulf

The nations on the shoreline of the Arabian/Persian Gulf are the world's largest users of desalination technologies, which are essential to meet their freshwater needs. Desalinated freshwater production is projected to rapidly increase in future decades. Thus, concerns have been raised that desalination activities may result in non-negligible long-term, basin-wide increases of salinity, which would have widespread detrimental effects on the Gulf marine ecosystems, with ripple effects on fisheries, as well as impacting the desalination activities themselves. We find that current yearly desalinated freshwater production amounts to about 2% of the net yearly evaporation from the Gulf. Projections to 2050 bring this value to 8%, leading to the possibility that, later in the second half of the century, desalinated freshwater production may exceed 10% of net evaporation, an amount which is comparable to interannual fluctuations in net evaporation. With the help of a model we examine several climatological scenarios, and we find that, under IPCC's SSP5-8.5 worst-case scenarios, end-of-century increases in air temperature may result in salinity increases comparable or larger to those produced by desalination activities. The same scenario suggests a reduced evaporation and an increased precipitation, which would have a mitigating effect. Finally we find that, owing to a strong overturning circulation, high-salinity waters are quickly flushed through the Strait of Hormuz. Thus, even in the worst-case scenarios, basin-scale salinity increases are unlikely to exceed 1 psu, and, under less extreme hypothesis, will likely remain well below 0.5 psu, levels that have negligible environmental implications at the basin-wide scale.

Market Opportunities of Water Treatments Powered by Solar Micro Gas Turbines: Chile and Ecuador Case Studies

Throughout the last decades the developments on desalination field have been focused on energy consumption and costs reduction. However, water recovery and brine disposal are becoming a matter of concern to desalination industry. In this work, a Zero Liquid Discharge (ZLD) unit coupled with a Solar Micro Gas Turbine (SMGT) system is presented to address, among others, the challenges of mining industry in remote areas, in particular, fossil fuel dependence, water availability and pollution derived from effluents disposal. As a way to assess the feasibility of the proposal, a techno-economic analysis of the application in two Southern American regions (Chile and Ecuador) of photovoltaic modules, wind turbines and Solar Micro Gas Turbines is performed. Afterwards, the main novel feature of the new system—i.e., the ZLD unit—is described and a sensitivity analysis on its functioning whilst coupled with the SMGT is carried out. The aim is to propose a preliminary design of the ZLD process. The selection of the optimal ratio between exhaust gases and brine mass flow rates is analyzed, as well as variation in inlet salinity and temperatures. Furthermore, the water which could be recovered from effluents, at the same time that the heat of exhaust gases from SMGT is harvested, is quantified. Lastly, according to the results obtained, a preliminary design of a 10 kWe rated power SMGT system, coupled to Reverse Osmosis (RO) and ZLD units, is proposed.

Spatial extent of desalination discharge impacts to habitat-forming species on temperate reefs

Outlet infrastructure and hypersaline discharge from large-scale desalination operations have the potential to impact marine environments. Here, we present the results of a six-year M-BACI assessment of the impacts of desalination discharge outlet construction and hypersaline effluent on the cover of habitat-forming species on temperate reefs. The construction of the desalination outlet caused a decrease in the cover of Ecklonia radiata (kelp) and an increase in the cover of algal turfs up to 55 m from the outlet. Following the commencement of discharging of hypersaline brine, the impact to E. radiata and algal turfs persisted, but decreased in spatial extent to be less than 25 m from the outlet. Hypersaline discharge was also associated with a significant decline in the cover of sponges in outlet compared to reference sites. Overall, our results demonstrate that the water security benefits from large-scale desalination may sometimes be appropriately balanced against the associated ecological consequences.

Is the development of desalination compatible with sustainable development of the Arabian Gulf?

The development of desalination has been essential to the rapid economic development of the countries bordering the Arabian Gulf. The current production capacity of sea water desalination plants drawing water from Gulf is over 20 million m³ day^-1, which may rise to 80 million m³ day^-1 by 2050. Whilst supporting aspects of sustainable development related to water and sanitation, desalination impacts the marine environment through impingement and entrainment of organisms in intakes, and through thermal, brine and chemical discharges. This may compromise other objectives for sustainable development related to sustainable use of the oceans. Under business as usual scenarios, by 2050, the impact of individual desalination plants will combine causing a regional scale impact. Without mitigating actions to avoid the business as usual scenario, by 2050, desalination in combination with climate change, will elevate coastal water temperatures across more than 50% of the Gulf by at least 3 °C, and a volume of water equivalent to more than a third of the total volume of water between 0 and 10 m deep will pass through desalination plants each year. This will adversely impact the coastal ecosystem of the Gulf, with impacts on biodiversity, fisheries and coastal communities and may cause potential loss of species and habitats from the Gulf. Given the significant implications of these preliminary findings, and in light of the precautionary approach to management, it is recommended that mitigating options addressing behavioural, regulatory and technological change are rapidly evaluated and implemented to avoid the development of desalination in the region along a business as usual pathway, and multidisciplinary research studies should be conducted to reduce uncertainty in predictions of future impacts.

Desalination and environment: A critical analysis of impacts, mitigation strategies, and greener desalination technologies

The desalination of seawater is perceived as one of the most viable processes to fulfill the mounting demand for freshwater. Despite enormous economic, social, and health benefits offered by desalination, there are several concerns regarding its prospective environmental impacts (EIs). The objective of this work is to critically evaluate the potential EIs of seawater desalination, and assess the prospects of greener desalination. The EIs of desalination on marine environment, land, groundwater, and air quality was systematically reviewed. An attempt has been made to analyze the actuality of these so-called impacts with reference to evidence from real desalination plants. The mitigative measures to counterbalance these unfavorable impacts are critically appraised. Furthermore, the brine management technologies for the disposal of reject stream, the recovery of precious materials and water, and the production of useful chemicals are also reviewed. Current challenges to minimize the adverse impacts of desalination and prospects of sustainable greener desalination to overwhelm global water scarcities are also discussed. The current desalination approaches have moderate and minor negative EIs. However, with proper mitigation and utilization of modern technologies, these impacts can be lessened. Furthermore, by employing various modern techniques, reject brine can be utilized for several useful applications while reducing its adverse impacts simultaneously. Recent advancements in desalination technologies have also offered many alternative approaches that provide a roadmap towards greener desalination. This review article will be beneficial for all the stakeholders in the desalination industry.

Environmental Remediation of Desalination Plant Outfall Brine Discharge from Heavy Metals and Salinity Using Halloysite Nanoclay

Halloysite (HS) nanoclay was used for the environmental treatment of desalination brine water discharge via the adsorptive removal of selected heavy metals ions; zinc, iron, nickel, and copper, as well as salinity. Different techniques were used for the characterization of the HS nanoclay and it was found that HS nanoclay exists as transparent hollow nanotubes with high surface area. The study showed that most of the heavy metal ions could be removed successfully using the HS nanoclay in a few minutes, at normal conditions. The adsorptive removal of zinc, iron, nickel, and copper, as well as salinity on HS nanoclay was explored kinetically. It was concluded that the pseudo-second-order kinetic model was able to describe the remediation process. In addition, it was found that most of the heavy metals and salinity were removed from the desalination plant outfall brine discharge and the final concentrations were lower than those in the control and standard samples.

Environmental impacts of desalination and brine treatment - Challenges and mitigation measures

Desalination is perceived as an effective and reliable process for obtaining freshwater from aqueous saline solutions such as brackish water, seawater and brine. This can be clarified by the fact that >300 million people worldwide rely on desalinated water for their daily needs. Although the desalination process offers many advantages, there are rising concerns about possible adverse environmental impacts. Generally, environmental impacts can be generated both in the construction and operation of desalination plants. A major issue of desalination is the co-produced waste called 'brine' or 'reject' which has a high salinity along with chemical residuals and is discharged into the marine environment. In addition to brine, other main issues are the high energy consumption of the desalination and brine treatment technologies as well as the air pollution due to emissions of greenhouse gasses (GHGs) and air pollutants. Other issues include entrainment and entrapment of marine species, and heavy use of chemicals. The purpose of this review is to analyze the potential impacts of desalination and brine treatment on the environment and suggest mitigation measures.

Hypersaline water from desalinization plants causes oxidative damage in Posidonia oceanica meadows

Posidonia oceanica is an endemic marine phanerogam of the Mediterranean Sea for that is very sensitive to the environmental changes, especially those related to human activities. The aim of this study was to evaluate the oxidative stress status of P. oceanica meadows exposed to spillage of hypersaline water from a desalination station by using biomarkers. Leaf samples of P. oceanica were obtained from 4 different points exposed to different levels of salinity water. Samples from the area with the highest salinity conditions were 75% shorter than the samples from the control area. Exposure to high salinity induced an increase in the levels of oxidative stress markers (malondialdehyde (MDA) and protein carbonyls). Interestingly, in the area with the highest salinity the activities of glutathione peroxidase, glutathione reductase and glutathione-s-transferase were significantly induced respect to the other studies areas, while catalase (CAT) and superoxide dismutase (SOD) activities were lower. In addition, salinity induced a progressive increase in non-enzymatic antioxidants (polyphenols and glutathione) and in total antioxidant capacity reaching the highest concentrations in samples directly affected by the saline discharge. In conclusion chronic exposure to high salinity induced an increase in total antioxidant capacity in P. oceanica. However, this increase was not enough to protect the plant against oxidative stress as it is evidenced by the raise in oxidative stress markers. The obtained data suggest that high salinity conditions deactivated CAT and SOD antioxidant enzymes and caused an increase in non-enzymatic antioxidants (polyphenols and glutathione) and in glutathione-related enzymes.

Revisiting Mean Flow and Mixing Properties of Negatively Round Buoyant Jets Using the Escaping Mass Approach (EMA)

The flow formed by the discharge of inclined turbulent negatively round buoyant jets is common in environmental flow phenomena, especially in the case of brine disposal. The prediction of the mean flow and mixing properties of such flows is based on integral models, experimental results and, recently, on numerical modeling. This paper presents the results of mean flow and mixing characteristics using the escaping mass approach (EMA), a Gaussian model that simulates the escaping masses from the main buoyant jet flow. The EMA model was applied for dense discharge at a quiescent ambient of uniform density for initial discharge inclinations from 15° to 75°, with respect to the horizontal plane. The variations of the dimensionless terminal centerline and the external edge’s height, the horizontal location of the centerline terminal height, the horizontal location of centerline and the external edge’s return point as a function of initial inclination angle are estimated via the EMA model, and compared to available experimental data and other integral or numerical models. Additionally, the same procedure was followed for axial dilutions at the centerline terminal height and return point. The performance of EMA is acceptable for research purposes, and the simplicity and speed of calculations makes it competitive for design and environmental assessment studies.

Copper Tailing Flocculation in Seawater: Relating the Yield Stress with Fractal Aggregates at Varied Mixing Conditions

The implications of physical conditions of the feedwell on the rheological properties of synthetic copper tailings, flocculated in seawater, were analysed. The mixing intensity of flocculation was related to the structural characteristics of the aggregates, and the outcomes were linked to the yield stress of the pulp sediments. Tailings settling assays were conducted by using a 30 mm turbine type stirrer with an in-situ aggregate size characterisation. The structural characteristics of the aggregates were determined by using the focused beam reflectance measurement (FBRM). After a mixing time between the pulp and the flocculant, the sample was allowed to settle for 2.5 h, where the variation of the sediment height was minimal. The sediment was gently removed and subjected to rheological characterisation. The yield stress was measured on an Anton Paar MCR 102 rheometer (ANAMIN Group, Santiago, Chile), with a vane-in-cup configuration. The mixing intensity was related to the characteristics of the aggregates, and the outcomes were linked to the yield stress of the flocculated pulp sediments. More aggressive hydrodynamics deteriorated the structure of the aggregates, promoting the reduction of both its size and the fractal dimension. This brought direct consequences on the rheological properties of the sediments: at higher mixing level, the yield stress was lower. The explanation lies in the structural changes of the aggregates, where at a fixed mixing rate, the yield stress presented a seemingly exponential increase over the fractal dimension. Additionally, correlations were found between the rheological properties with settling rate and aggregate size.