The effect of coagulants and antiscalants discharged with seawater desalination brines on coastal microbial communities: A laboratory and in situ study from the southeastern Mediterranean

Assessment of brine discharges dispersion for sustainable management of SWRO plants on the South American Pacific coast

Seawater desalination is one of the most feasible technologies for producing fresh water to address the water scarcity scenario worldwide. However, environmental concerns about the potential impact of brine discharge on marine ecosystems hinder or delay the development of desalination projects. In addition, scientific knowledge is lacking about the impact of brine discharges on the South America Pacific coast where desalination, is being developed. This paper presents the first monitoring results of brine discharge influence areas from seawater reverse osmosis desalination plants (SWRO) on the South America Pacific coast, using Chile as case study. Our results indicate that the combination of favorable oceanographic conditions and diffusers, results in the rapid dilution of brine discharge on coastal ecosystems; showing a faster dilution than other SWRO plants in other regions, such as Mediterranean or Arabian Gulf, with similar production characteristics. Also, the increase in salinity over the natural salinity in the brine-discharge-affected area was <5 % in a radius of <100 m from the discharge points. Further, according to the published literature and on our monitoring results, we propose a number of considerations (environmental regulation, best scientifically tested measures, environmental requirements) to achieve a long-term sustainable desalination operation.

Effects of coagulation pre-treatment on chemical and microbial properties of water-soil-plant systems of constructed wetlands

Chemical coagulation has gained recognition as an effective technique to enhance the removal efficiency of pollutants in wastewater prior to their entry into a constructed wetland (CW) system. However, its potential impact on the chemical and microbial properties of soil and plant systems within CWs requires further research. This study investigated the impact of using ferric chloride (FeCl3) as a pre-treatment stage for dairy wastewater (DWW) on the chemical and microbial properties of water-soil-plant systems of replicated pilot-scale CWs, comparing them to CWs treating untreated DWW. CWs treating amended DWW had better performance than CWs treating raw DWW for all water quality parameters (COD, TSS, TP, and TN), ensuring compliance with the EU wastewater discharge directives. Soil properties remained mostly unaffected except for pH, calcium and phosphorus (P), which were lower in CWs treating amended DWW. As a result of lower nitrogen (N) and P loads, the plants in CWs receiving FeCl3-amended DWW had lower N and P contents than the plants of raw DWW CWs. However, the lower loads of P into amended DWW CWs did not limit the growth of Phragmites australis, which were able to accumulate trace elements higher than CWs receiving raw DWW. Alpha and Beta-diversity analysis revealed minor differences in community richness and composition between both treatments, with only 3.7% (34 genera) showed significant disparities. Overall, the application of chemical coagulation produced superior effluent quality without affecting the properties of soil and plant of CWs or altering the functioning of the microbial community.

Non-target screening and prioritization of organic contaminants in seawater desalination and their ecological risk assessment

The impact of desalination brine on the marine environment is a global concern. Regarding this, salinity is generally accepted as the major environmental factor in desalination concentrate. However, recent studies have shown that the influence of organic contaminants in brine cannot be ignored. Therefore, a non-targeted screening method based on comprehensive two-dimensional gas chromatography-quadrupole mass spectrometry (GC × GC-qMS) was developed for identifying organic contaminants in the desalination brine. A total of 404 compounds were tentatively identified from four seawater desalination plants (three reverse osmosis plants and one multiple effect distillation plant) in China. The identified compounds were prioritized based on their persistence, bioaccumulation, ecotoxicity, usage, and detection frequency. Twenty-one (21) compounds (seven phthalates, ten pesticides, four trihalomethanes) were then selected for further quantitative analysis and ecological risk assessment, including compounds from the priority list along with substances from the same chemical classes. Ecologically risky substances in brine include diisobutylphthalate and bis(2-Ethylhexyl) phthalate, atrazine and acetochlor, and bromoform. Most of the contaminants come from raw seawater, and no high risk contaminants introduced by the desalination process have been found except for disinfection by-products. In brine discharge management, people believed that all pollution in raw seawater was concentrated by desalination process. This study shows that not all pollutants are concentrated during the desalination process. In this study, the total concentration of pesticide in the brine increased by 58.42%. The concentration of ∑PAEs decreased by 13.65% in reverse osmosis desalination plants and increased by 10.96% in the multi-effect distillation plant. The concentration of trihalomethane increased significantly in the desalination concentrate. The change in the concentration of pollutants in the desalination concentrate was related to the pretreatment method and the chemical characteristics of the contaminants. The method and results given in this study hinted a new idea to identify and control the environmental impact factors of brine.

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.

Impacts of desalination discharges on phytoplankton and zooplankton: Perspectives on current knowledge

Large-scale application of desalination technology can result in impacts to the marine biota, such as phytoplankton and zooplankton, basal components of marine trophic webs. In this context, our perspective aimed to summarize the impacts of effluent discharges from desalination plants on phytoplankton and zooplankton in order to identify the main gaps and challenges in this theme, propose solutions, and provide recommendations for future work. We identified two main approaches to assess the desalination impacts: laboratory experiments and field studies. Most of these studies were conducted in areas impacted by effluent discharges using the BACI (before, after, and control-impact) approach. They primarily aimed to set out the impacts of hypersaline brine on the surrounding environment and, to a lesser extent, the high-temperature effluents and contaminants from desalination plants. Moreover, phytoplankton was more sensitive to effluent discharges than zooplankton. The main changes observed were a decrease in primary productivity, a loss in diversity, and a change in the community structure of planktonic populations due to the dominance of saline-tolerant groups, which highlights the importance improving treatment or dilution of effluent discharges to minimize the impacts over whole neritic trophic webs, which depend on phytoplankton. From the impacts related to effluent discharges analyzed herein, RO technology was related to most cases of negative impact related to salinity modifications. However, coagulants were related to negative effects in all study cases. Future work should focus on escalate the impacts of such effluents on other trophic levels that could be directly or indirectly impacted as well as on how to improve the quality of effluent discharges. Also, we highlight the importance of further baseline and long-term monitoring studies to investigate desalination-induced changes and community resilience to these impacts, as well as studies to provide alternatives to the use of toxic chemicals in the pre-treatment phases.

Antiscalants used in the desalination industry impact the physiology of the coral Montipora capricornis

Many coral reefs are found in arid and semi-arid regions that often face severe water scarcity and depend on seawater desalination for freshwater supply. Alongside freshwater production, desalination plants discharge brine waste into the sea. Brine includes various chemicals (e.g., antiscalants) that may harm the coastal environment. Although widely used, little is known about the ecotoxicological effects of antiscalants (AS) on hard corals. This study compared the impacts of polyphosphonate-based and polymer-based ASs on the coral Montipora capricornis. After two weeks of exposure, we determined the effects of AS on coral physiology, symbiotic microalgae, and associated bacteria, using various analytical approaches such as optical coherence tomography, pulse amplitude modulated fluorometry, and oxidative stress biomarkers. Both ASs reduced polyp activity (∼25%) and caused tissue damage (30% and 41% for polymer and polyphosphonate based AS, respectively). In addition, exposure to polyphosphonate-based AS decreased the abundance of endosymbiotic algae (39%) and upregulated the antioxidant capacity of the animal host (45%). The microalgal symbionts were under oxidative stress, with increased levels of antioxidant capacity and oxidative damage (a 2-fold increase compared to the control). Interestingly, exposure to AS enhanced the numbers of associated bacteria (∼40% compared to the control seawater) regardless of the AS type. Our results introduce new insights into the effects of brine on the physiology of hard corals, highlighting that choosing AS type must be examined according to the receiving ecosystem.

Discharge of Polyphosphonate-Based Antiscalants via Desalination Brine: Impact on Seabed Nutrient Flux and Microbial Activity

Desalination brine is a hypersaline byproduct that contains various operational chemicals such as polyphosphonate-based antiscalants. Brine often sinks and flows over the seabed by density currents; therefore, it may affect sediment-water nutrient fluxes and thus microbial activity. We quantified these parameters in brine plumes around two large-scale desalination facilities located in the P-limited Southeastern Mediterranean Sea. The benthic nutrient fluxes and microbial activity were determined using ex-situ core benthocosms, to which we added brine from the dispersion area in excess salinities of ∼3% and 5% above natural levels. A higher influx of dissolved organic phosphorus (∼6-fold) and an efflux of dissolved organic carbon (∼1.7-fold) were measured in the brine-amended cores relative to the controls. This was accompanied by increased oxygen consumption (15%) and increased microbial activity (∼1.5-6.5-fold). Field observations support the results from experimental manipulations, yielding ∼4.5-fold higher microbial activity rates around the brine plume compared to uninfluenced locations. Our results imply that desalination brine can alter sedimentary processes affecting benthic nutrients inventories. Moreover, we show that brine acts as a vector of anthropogenic P, stimulating microbial activity in the sediment-water interface.

Antiscalants Used in Seawater Desalination: Biodegradability and Effects on Microbial Diversity

Antiscalants are organic polymers widely used for scale inhibition in seawater desalination. While they are susceptible to biodegradation, they provide nutrients for bacterial cell growth and energy for the microbes that assimilate and degrade them. This paper shows the biodegradability of three commercial antiscalants (polyacrylate—CA, polyphosphonate—PP, and carboxylated dendrimers—DN) applied in seawater reverse osmosis desalination (SWRO) as well as analyzing the antiscalant’s effects on microbial diversity using microbial cultures grown in seawater, under semi-continuous batch conditions. Nutritional uptake and contribution of the antiscalants to microbial growth were investigated by measuring DOC, TDN, NO₃⁻, NO₂⁻, PO₄⁻, NH₄⁺, and TP of the filtered samples of the incubated batch, twice a month, for twelve months. The microbial community was estimated by 16S rRNA sequencing. The main changes in the microbial communities were determined by the incubation period. However, bacterial orders of the antiscalant treatments differed significantly from the control treatment, namely Planctomycetales, Clostridiales, Sphingobacteriales, Rhodobacterales, and Flavobacteriales, and other unclassified bacterial orders, which were found in various relative abundances dependent on incubation times. The results showed the PP antiscalant to be the least biodegradable and to have the least effect on the bacterial community composition compared to the control. This result emphasizes the need to reassess the suitability criteria of antiscalants, and to further monitor their long-term environmental effects.

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.

Reverse Osmosis Concentrate: Physicochemical Characteristics, Environmental Impact, and Technologies

This study's aim is to generate a complete profile of reverse osmosis concentrate (ROC), including physicochemical characteristics, environmental impact, and technologies for ROC treatment, alongside element recovery with potential valorization. A systematic literature review was used to compile and analyze scientific information about ROC, and systematic identification and evaluation of the data/evidence in the articles were conducted using the methodological principles of grounded data theory. The literature analysis revealed that two actions are imperative: (1) countries should impose strict regulations to avoid the contamination of receiving water bodies and (2) desalination plants should apply circular economies. Currently, synergizing conventional and emerging technologies is the most efficient method to mitigate the environmental impact of desalination processes. However, constructed wetlands are an emerging technology that promise to be a viable multi-benefit solution, as they can provide simultaneous treatment of nutrients, metals, and trace organic contaminants at a relatively low cost, and are socially accepted; therefore, they are a sustainable solution.

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.

Salinity reduction of brackish water using a chemical photosynthesis desalination cell

In this study, a chemical photosynthesis desalination cell (CPDC) was investigated for saltwater desalination. The cell consisted of three main parts: (1) an anodic compartment where the oxidation reaction occurs, releasing electrons, (2) a cathode compartment where the required soluble oxygen is provided by microalgae photosynthesis, and (3) an electrodialysis desalination cell installed between the cathode and anode. In the anode, a novel idea was adopted to shorten the desalination duration and increase the salinity rate using a chemical oxidation reaction in combination with the biocathode. The CPDC contributed to the carbon dioxide biological sequestration (reducing air pollution), produced microalgae biomass as a source of renewable energy and generated electricity. In the investigated CPDC, microalgae were used to supply the required oxygen solution as an electron acceptor. The metal anode-microalgae biocathode battery could provide the required energy for electrodialysis. In addition, some extra electricity was generated with a maximum excess power density of 32.4 W/m³ per volume of the net anodic compartment, 16.2 W/m³ per volume of the net cathodic compartment, and 3.07 W/m² of membrane surface area. This study confirms the benefits of microalgae as a sustainable biocathode in microbial desalination cells (MDCs) to supply electron acceptors in an environmental-friendly manner. Compared to photosynthetic microbial desalination cells (PMDCs), the CPDC decreased the desalination time by a factor of about 4. Besides, the NaCl removal was about 69% for 12 g/L NaCl concentration in the CPDC, higher than other MDCs. In addition, as a new operational factor, the internal resistance variations were determined by electrochemical impedance spectroscopy in different case studies. The results demonstrated for the first time the possibility of applying a new desalination cell (i.e. CPDC) for water desalination and power generation which only uses a source of chemical reaction and microalgae photosynthesis without the need for an external power source.

Environmental impact of desalination technologies: A review

Due to the limited availability of freshwater supplies, desalination has become an increasingly reliable process for water supply worldwide, with proved technical and economic feasibility and advantages. Recently, desalination capacity significantly increased from approximately 35 million m³ daily (MCM/day) in 2005 to about 95 MCM/day in 2018. Seawater desalination accounts for about 61% of global desalination capacity, while brackish water desalination accounts for 30%. Membrane desalination, mainly using reverse osmosis (RO), accounts for ¾ of global desalination capacity, with the rest mostly used for thermal desalination using multi-stage flash distillation (MSF), and multi-effect distillation (MED). Despite the undeniable role of desalination for securing water supply in areas where natural freshwater supplies are scarce, desalination impacts the natural environment at different aspects. Environmental impacts (EIs) of the desalination process are different and vary significantly according to the nature of the utilized feedwater, the desalination technology in use, and the management of waste brine generated. In this work, the EIs of each desalination technology were thoroughly investigated, with careful consideration given to different feedwater qualities, and various brine management techniques. Although the different aspects of desalination EIs have been extensively studied in the literature, the literature lacks comprehensive reviews and summaries of all the associated EIs. This article compiles the different EIs associated with the whole desalination process in one-hub, applying an intake-to-outfall approach. The leading desalination technologies of RO, MSF, and MED were analyzed, along with different feedwaters. This article provides a mapping of the different technologies involving feedwater and brine management techniques and a detailed description of their impact on the environment. Finally, recommendations and conclusions were given to minimize the negative impacts of desalination on both the local and global environments.

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.

Environmental impact of desalination processes: Mitigation and control strategies

Freshwater supplies are in shortage relative to the high demand for different human activities, making desalination of saline water a must. Desalination to extract water from saline water has been well established as a reliable non-conventional water supply. However, desalination as any human-based process has resulted in many impacts on the environment. Brine loaded with chemicals being discharged back to the environment, along with greenhouse gases (GHGs) emissions being released to the atmosphere, are the most significant impacts, which has been extensively studied, with some efforts given to its mitigation and control. The current work discusses the mitigation and control strategies (M&CS) to the different environmental impacts (EIs) of desalination processes. The article compiles the M&CS in one work, instead of the distributed and separate treatment of the EIs of each desalination step and its respective M&CS as currently present in literature. The article tracks the water flow in an intake-to-outfall approach exploring how to minimize the impacts at each step and as a whole process. This starts from intake, pretreatment processes, desalination technology, and finally, brine discharge. The EIs associated with each desalination process element is thoroughly discussed with proposed M&CS. The work shows clearly that many EIs can be eliminated or minimized by incorporating specific design criteria and process improvements. The feedwater source has shown to have a great effect on EIs. Similarly, desalination technology has shown a considerable effect on the EIs related to brine characteristics and energy consumption. Hybrid and emerging desalination systems have shown reduced EIs relative to conventional thermal and membrane desalination technologies, while the utilization of renewable and waste energy sources has shown a significant reduction in EIs related to energy consumption.

Modelling the distributions of desalination brines from multiple sources along the Mediterranean coast of Israel

We use numerical simulations to study the possible spatiotemporal effects of brine release from five desalination plants, located along the Israeli Mediterranean coastline. It is commonly believed that salinity anomalies, associated with brine discharge from desalination plants, causes effects which are confined to an area of several hundreds of meters from the discharge outfall. We show that discharging brine using diffusers produces small but robust salinity anomalies that propagate tens of kilometers as density currents (DCs). In contrast, premixing the brine with power plant cooling water compensates the negative buoyancy and prevents their generation. The propagating DCs can impact coastal water dynamics by increasing the velocities and transports in alongshore and downslope directions. The spreading and trajectories of the DCs was strongly influenced by seasonal stratification. In winter, due to a mixed water column, the DCs were relatively focused and propagate downslope. While in the summer they are confined to a narrow band along the coastline. Our model results highlight the possibility that brine discharge might have a large scale, non-negligible effect on shelf circulation than previously considered. Further studies are needed to assess the environmental, dynamical and ecological effects of desalination brine propagation, especially in the far field.

Seawater quality at the brine discharge site from two mega size seawater reverse osmosis desalination plants in Israel (Eastern Mediterranean)

Two mega-size seawater desalination plants, producing 240 Mm³/y freshwater, discharge brine into the Mediterranean coast of Israel through two marine outfalls, located 0.8 km apart. Six years monitoring brine discharge have shown almost no impact on seawater quality. The brine dispersed near the bottom following its initial mixing, and was not detected near the surface. Maximal excess salinity at the salty layer ranged from 4.3 to 9.1% over the reference and the affected area was highly variable (2 km² - >13 km²), with maximal plume size from 1.75 to more than 4.4 km. Brine increased seawater temperature by up to 0.7 °C near the outfalls. It had no impact on oxygen saturation, turbidity, pH, nutrients (except for total organic phosphorus (TOP)), chlorophyll-a and metal concentrations. TOP, from the polyphosphonate-based antiscalant discharged with the brine, was correlated with excess salinity. It is unknown if the results of this short term study represent a steady state, with temporal variability, or the beginning of a slow incremental impact. Israel is planning to more than double desalination along its 190 km Mediterranean coast by 2050. A long term, adaptable, program, in conjunction with specific research and modeling, should be able to assess and predict the impact of large scale brine discharge on the marine environment.

Environmental sustainability assessment of seawater reverse osmosis brine valorization by means of electrodialysis with bipolar membranes

The integration of electrodialysis with bipolar membranes (EDBM) with seawater reverse osmosis (SWRO) process influences the two main environmental burdens of SWRO desalination process: climate change, accounted here as carbon footprint (CF) and associated to the high-energy consumption, and the environmental alteration of the vicinities of the facility, due to brine disposal. EDBM powered by photovoltaic (PV) solar energy is able to meet the above-mentioned challenges that arise in SWRO desalination. In addition, HCl and NaOH, both employed in the desalination industry, can be produced from the brines. Hence, environmental benefits regarding the potential self-supply can be achieved. The environmental sustainability assessment by means of life cycle assessment (LCA) of a SWRO and EDBM has been carried out considering four different scenarios. The percentage of treated brines and the influence of the grid mix used for electric power supply has been taken into account. The three different electric power supplies were 100.0% renewable energy (PV solar energy), 36.0% renewable energy (average Spanish grid mix), and 1.9% (average Israeli grid mix). The results showed that the CF per unit of volume produced freshwater for SWRO and the self-supply reagent production scenario for the three Spanish grid mix, the Israeli grid mix, and the PV solar energy were 6.96 kg CO₂-eq·m^-3, 12.57 kg CO₂-eq·m^-3, and 2.17 kg CO₂-eq·m^-3, respectively.

Desalination brine disposal methods and treatment technologies - A review

Brine, also known as concentrate, is the by-product of the desalination process that has an adverse impact on the environment due to its high salinity. Hence, viable and cost-effective brine management systems are needed to reduce environmental pollution. Currently, various disposal methods have been practiced, including surface water discharge, sewer discharge, deep-well injection, evaporation ponds and land application. However, these brine disposal methods are unsustainable and restricted by high capital costs and non-universal application. Nowadays, brine treatment is considered one of the most promising alternatives to brine disposal, since treatment results in the reduction of environmental pollution, minimization of waste volume and production of freshwater with high recovery. This review article evaluates current practices in brine management, including disposal methods and treatment technologies. Based upon the side-by-side comparison of technologies, a brine treatment technology framework is introduced to outline the Zero Liquid Discharge (ZLD) approach through high freshwater recovery and wastewater volume minimization. Furthermore, an overview of brine characteristics and its sources, as well as its negative impact on the environment is discussed. Finally, the paper highlights future research areas for brine treatment technologies aiming to enhance the effectiveness and viability of desalination.

Effect of the membrane exclusion mechanism on phosphate scaling during synthetic effluent desalination

Calcium phosphate scaling is one of the main limitations in effluent desalination using membranes. This may be overcome by tailoring membranes with lower rejection of the scalant ions. In this study, we systematically examined the use of negatively and positively charged membranes, rejecting ions mainly based on Donnan exclusion, as a low-scaling alternative to dielectric-exclusion-dominated polyamide NF membranes for effluent desalination. The two charged membranes exhibited a lower calcium and especially phosphate rejection than the polyamide membrane. Consequently, the calcium phosphate supersaturation and then the propensity to scaling of the charged membranes were much lower than the polyamide membrane. This also allowed filtering at a much higher recovery ratio with the charged membranes. It was also found that, despite the fact that the charged membranes had an opposite fixed charge, their scaling behavior was similar. Apparently, although these membranes showed opposite selectivity towards scalant ions (phosphate and calcium) in single salt solutions, the rejection pattern in mixed salt solutions resulted in similar saturation indices, much lower than for polyamide membrane. The scale formed on all three membranes was identified as amorphous calcium phosphate (ACP), although its saturation index was lower than its solubility factor. This was explained by concentration polarization which increases the saturation index in the solution adjacent to the membrane surface. Tests in absence of permeate flux showed a much slower precipitation that took a few days compared with filtration conditions (few hours). In addition, under these conditions, the effect of the scaling on the membrane permeability was generally reduced and the scale contained crystalline calcium phosphate products, different from ACP. The results indicate that the ion rejection and resulting polarization next to the membrane surface plays a crucial role in scaling. Thus, tuning ion selectivity of NF membranes towards scalant ions presents a promising alternative for scaling mitigation during effluent desalination.

DOP Stimulates Heterotrophic Bacterial Production in the Oligotrophic Southeastern Mediterranean Coastal Waters

Phytoplankton and heterotrophic bacteria rely on a suite of inorganic and organic macronutrients to satisfy their cellular needs. Here, we explored the effect of dissolved inorganic phosphate (PO₄) and several dissolved organic molecules containing phosphorus [ATP, glucose-6-phosphate, 2-aminoethylphosphonic acid, collectively referred to as dissolved organic phosphorus (DOP)], on the activity and biomass of autotrophic and heterotrophic microbial populations in the coastal water of the southeastern Mediterranean Sea (SEMS) during summertime. To this end, surface waters were supplemented with PO₄, one of the different organic molecules, or PO₄ + ATP, and measured the PO₄ turnover time (Tt), alkaline phosphatase activity (APA), heterotrophic bacterial production (BP), primary production (PP), and the abundance of the different microbial components. Our results show that PO₄ alone does not stimulate any significant change in most of the autotrophic or heterotrophic bacterial variables tested. ATP addition (alone or with PO₄) triggers the strongest increase in primary and bacterial productivity or biomass. Heterotrophic bacterial abundance and BP respond faster than phytoplankton (24 h post addition) to the various additions of DOP or PO₄ + ATP, followed by a recovery of primary productivity (48 h post addition). These observations suggest that both autotrophic and heterotrophic microbial communities compete for labile organic molecules containing P, such as ATP, to satisfy their cellular needs. It also suggests that SEMS coastal water heterotrophic bacteria are likely C and P co-limited.

Phytoplankton response to N-rich well amelioration brines: A mesocosm study from the southeastern Mediterranean Sea

Human-induced eutrophication of coastal water may be a major threat to aquatic life. Here, we investigated the effects of N-rich well amelioration brines (WAB) on coastal phytoplankton population's habitat in the surface oligotrophic waters of the southeastern Mediterranean Sea (SEM). To this end, we added WAB (2 concentrations) to mesocosms (1-m³ bags) to surface SEM water during summer and winter, where changes in phytoplankton biomass, activity and diversity was monitored daily for 8 days. Our results demonstrate that WAB addition triggered a phytoplankton bloom, resulting in elevated algal biomass (maximal +780%), increased primary production rates (maximal +675%) and a decrease in eukaryotic algal α-diversity (ca. -20%). Among the species that bloomed following WAB amendments, we found the potentially toxic dinoflagellate Karlodinium venificum. This study adds valuable perspective to the effect of nutrients discharged into nutrient limited SEM coastal waters, and in particular of N-derived WAB.

Degradation of nitrilotris-methylenephosphonic acid (NTMP) antiscalant via persulfate photolysis: Implications on desalination concentrate treatment

Nitrilotris-methylenephosphonic acid (NTMP) has been widely used as an antiscalant in reverse osmosis (RO) desalination and other industrial processes to inhibit scaling from calcium and other hardness ions. Removal of NTMP from RO concentrate can induce the precipitation of oversaturated scale-forming substances, enable additional water recovery from RO concentrate, and reduce the risk of eutrophication after brine disposal. This study investigated the kinetics and mechanisms of oxidative degradation of NTMP by UV photolysis of persulfate at 254 nm. Results showed that NTMP was effectively degraded by persulfate photolysis and the reaction followed pseudo first-order kinetics. The degradation of NTMP was favorable at circumneutral pHs but significantly inhibited in highly alkaline conditions (e.g., pH of 11.5), mainly due to the reduced concentration of SO₄^•-. Using a competition reaction kinetics approach, the second-order rate constants of NTMP with SO₄^•- and HO^• were determined to be (2.9 ± 0.6) × 10⁷ M^-1s^-1 and (1.1 ± 0.1) × 10⁸ M^-1s^-1, respectively. SO₄^•- had a predominant contribution to NTMP degradation (62%-95%), because the steady-state concentration of SO₄^•- was 11-54 times higher than that of HO^• at pHs between 4 and 11.5. NTMP degradation rate increased with an increase in persulfate dosage and a decrease in NTMP concentration. In the real RO concentrate, NTMP degradation rate was impacted by the presence of chloride and bicarbonate. The degradation of NTMP started with the cleavage of C-N bonds, and then generated intermediates including iminodi(methylene)phosphonate, hydroxymethylphosphonic acid and aminotris(methylenephosphonic acid), which were eventually mineralized into ammonia, phosphate and carbon dioxide. This study demonstrated that UV/persulfate is a promising technology to remove phosphonate antiscalants from RO concentrate.

Chronic effects of brine discharge form large-scale seawater reverse osmosis desalination facilities on benthic bacteria

Seawater desalination facilities continuously discharge hyper-saline brine into the coastal environment which often flows as a concentrated plume over the seafloor, hence possibly impacting benthic microorganisms. Yet, the effects of brine discharge from desalination plants on benthic bacteria, key players in biodegradation of organic material and nutrient recycling is unknown. In this study, we tested the chronic (years) effects of brine discharge from three large-scale desalination facilities on the abundance, metabolic activity and community composition of benthic bacteria. To this end, four sampling campaigns were carried at the outfall areas of the Ashkelon, Sorek and Hadera desalination facilities. The effects of the brine were compared to corresponding reference stations which were not influenced by the brine (i.e., water temperature and salinity). Our sampling data indicate that bacterial abundance and activity that includes bacterial growth efficiency were 1.3-2.6-fold higher at the outfall area than the reference station. Concomitant analysis pointed out that the bacterial community structure at the brine discharge area was also different than the reference station, yet varied between each desalination facility. Our results demonstrate that the impact of brine effluent from desalination facilities on benthic bacteria are site-specific and localized (<1.4 Km²) around the discharge point. Namely, that the effects on benthic bacteria are prominent at the brine mixing zone and change according to the discharge method used to disperse the brine as well as local stressors (e.g., eutrophication and elevated water temperature). Our results contribute new insights on the effects of desalination-brine to benthic microbes, while providing scientifically-based aspects on the ecological impacts of brine dispersion for decision makers.

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

Desalination has the potential to provide an important source of potable water to growing coastal populations but it also produces highly saline brines with chemical additives, posing a possible threat to benthic marine communities. The effects of brine (0%, 50%, 100%) were compared to seawater treatments with the same salinity (37, 46, 54 psu) for seagrass (Posidonia australis) in mesocosms over 2 weeks. There were significant differences between brine and salinity treatments for photosynthesis, water relations and growth. Germinating seedlings of P. australis were also tested in brine treatments (0%, 25%, 50%, 100%) over 7 weeks followed by 2.5 weeks recovery in seawater. Growth was severely inhibited only in 100% brine. These experiments demonstrated that brine increased the speed and symptoms of stress in adult plants compared to treatments with the same salinity, whereas seedlings tolerated far longer brine exposure, and so could potentially contribute to seagrass recovery through recruitment.

Biological and Physical Effects of Brine Discharge from the Carlsbad Desalination Plant and Implications for Future Desalination Plant Constructions

Seawater reverse osmosis (SWRO) desalination is increasingly used as a technology for addressing shortages of freshwater supply and desalination plants are in operation or being planned world-wide and specifically in California, USA. However, the effects of continuous discharge of high-salinity brine into coastal environments are ill-constrained and in California are an issue of public debate. We collected in situ measurements of water chemistry and biological indicators in coastal waters (up to ~2 km from shore) before and after the newly constructed Carlsbad Desalination Plant (Carlsbad, CA, USA) began operations. A bottom water salinity anomaly indicates that the spatial footprint of the brine discharge plume extended about 600 m offshore with salinity up to 2.7 units above ambient (33.2). This exceeds the maximum salinity permitted for this location based on the California Ocean Plan (2015 Amendment to Water Quality Control Plan). However, no significant changes in the assessed biological indicators (benthic macrofauna, BOPA-index, brittle-star survival and growth) were observed at the discharge site. A model of mean ocean wave potential was used as an indicator of coastal mixing at Carlsbad Beach and at other locations in southern and central CA where desalination facilities are proposed. Our results indicated that to minimize environmental impacts discharge should target waters where a long history of anthropogenic activity has already compromised the natural setting. To ensure adequate mixing of the discharge brine desalination plants should be constructed at high-energy sites with sandy substrates, and discharge through diffusor systems.

Impact of brine and antiscalants on reef-building corals in the Gulf of Aqaba - Potential effects from desalination plants

Seawater reverse osmosis (SWRO) is becoming an increasingly important source of potable water in arid and semi-arid regions worldwide. Discharge of brine-effluent from desalination facilities has been shown to significantly impact coastal marine ecosystems ranging from seagrass meadows to microbial communities. In this study, we examined the impacts of increased salinity (10% above ambient) and presence of antiscalants (0.2 mg L^-1, polyphosphonate-based) on three reef-building coral species; Stylophora pistillata, Acropora tenuis and Pocillopora verrucosa, from the Gulf of Aqaba (northern Red-Sea). Our results indicate that the corals, as well as associated bacteria and algae, were significantly impaired by the elevated salinity and antiscalants, leading to partial bleaching. Specifically, the abundance of bacteria and symbiotic algae as well as calcification rates were typically lower (20-85%, 50-90% and 40-50%, respectively) following incubations with both amendments. However, the impact of desalination brine was often species-specific. Thus, we propose that the ecotoxicological criteria used for hard corals should be determined based on the sensitivity of key species in the community dominating the area affected by desalination discharge.

Impact of nutrient enrichment on productivity of coastal water along the SE Mediterranean shore of Israel - A bioassay approach

The coastal waters of the southeastern Mediterranean-Sea (SEMS) are routinely enriched with naturally-occurring and anthropogenic land-based nutrient loads. These external inputs may affect autotrophic and heterotrophic microbial biomass and activity. Here, we conducted 13 microcosm bioassays with different additions of inorganic NO₃-(N), PO₄-(P) and Si(OH)₄-(Si) in different seasons along the Mediterranean coast of Israel. Our results indicate that cyanobacteria are mainly N-limited, whereas N or Si (or both) limit pico-eukaryotes. Furthermore, the degree to which N affects phytoplankton depends on the ambient seawater's inorganic N and N:P characteristics. Heterotrophic bacteria displayed no response in all treatments, except when all nutrients were added simultaneously, suggesting a possible co-limitation by nutrients. These results contrast the N+P co-limitation of phytoplankton and the P-limitation of bacteria in the open waters of the SEMS. These observations enable the application for a better science-based environmental monitoring and policy implementation along the SEMS coast of Israel.