Desalination Plant Discharges Research Articles

Multi-stage humidification–dehumidification system integrated with a crystallizer for zero liquid discharge of desalination brine

Desalination plants discharge a massive volume of brine every day, which negatively affects the ecosystem, particularly the subsurface ecology and marine life. To mitigate the brines' detrimental effects on the environment and facilitate the recovery of salt crystals and freshwater, the Zero Liquid Discharge (ZLD) approach was proposed. This study proposes four different configurations of multistage humidification dehumidification systems integrated with a crystallizer, exploring their energy and economic implications. Key findings from the study include the higher Gained Output Ratio (GOR) in series configurations due to lower temperature differences, resulting in lower heater energy consumption. The crystallizer significantly enhances water productivity, but it is a major consumer of both electricity (85%) and thermal energy (50.45–57.7%) in the system. Increasing the heat source temperature reduces the Specific Electrical Energy Consumption (SEEC) and the specific area while slightly increasing the Specific Thermal Energy Consumption (STEC). Elevated cooling water temperature raises SEEC and specific area but has negligible effects on STEC. Higher feed water flow rates increase SEEC but lower both STEC and specific area. Feed salinity elevation decreases productivity, SEEC, STEC, and specific area. The crystallizer constitutes 15.43–26.44% of the total capital cost, with series configurations incurring higher costs. Unit freshwater production costs, considering salt selling, range from 1.733 to 4.821 $.m−3. In a waste heat scenario, parallel configurations become profitable, where freshwater can be distributed at zero cost, while the produced salt crystals can be sold at an even lower price of $58.09 per tonne and $57.04 per tonne, respectively.

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.

The impact assessment of desalination plant discharges on heavy metal pollution in the coastal sediments of the Persian Gulf

In recent decades the development of desalination plants (DPs) for desalination of seawater has increased dramatically, while little attention has been paid to the effects of this activity on the accumulation of heavy metals (HMs) in the sediments of affected ecosystems. The present study was implemented to evaluate (1) heavy metal accumulation in sediments impacted by DPs discharges, (2) spatial and temporal changes of HMs and the contamination degree by different types of pollution indexes (single and integrated indices), and (3) ecological risk assessment of cadmium (Cd), lead (Pb), zinc (Zn) and copper (Cu) in sediments affected by DPs discharges. A total of 288 sediment samples were collected seasonally at 24 stations from November 2019 to October 2020. Analysis of HMs concentrations in sediments near the desalination plant discharge provided evidence of local contamination. Maximum concentration of Cu and Pb elements were found in sediments near the desalination plant discharge point. Hierarchical cluster analysis revealed clear segregation of stations impacted by desalination plant discharges and away from discharges. The values of PLI index in sediments of all sampling stations were < 1, indicating that there was no metal pollution by this index. The potential ecological risk index (PERI) ranged from 5.33 ± 0.51 to 11.81 ± 4.98 in sampling sediments and were classified as “low potential ecological risk”. These results demonstrate that the DPs discharge increased HMs concentrations in the sediments in close proximity to outlets. The necessary and practical regulations and policies regarding the rejection of the DPs discharge and disposal of chemical compounds must be implemented and enforced.

Use of Alternative Water Resources in Copper Leaching Processes in Chilean Mining Industry—A Review

Due to the significant growth of the world population, the accelerated growth of economic industries in various countries, and improved living conditions, freshwater consumption has increased dramatically and is currently under critical pressure. Its good use and rationing are essential. Even though mining is an industry that consumes much less water than other industries, such as agriculture, surrounding communities are constantly questioned. This occurs mainly because mining deposits are generally found in arid areas where freshwater is scarce, forcing government authorities to regulate water use in mining processes more severely. Faced with this scenario, the mining industry has innovated the use of seawater and wastewater from processes for its production processes. In addition, various projects are under development to construct desalination plants and water impulsion systems of the sea; therefore, it is expected that seawater and/or wastewater in mining will continue to grow in the coming years. Among the main challenges faced in the use of these water resources in mining is: (i) the close relationship that exists between the use of seawater and energy consumption, transferring the problem of water scarcity to a problem of energy cost overruns; (ii) generation of greater integration between the use of water and sustainable energy; and (iii) brine management is economically expensive and technically challenging and, therefore, most desalination plants discharge untreated brine directly into the sea, causing an environmental impact. On the other hand, regarding the use of these water resources in leaching processes, there are very positive results for the dissolution of copper from sulfide minerals, where the wastewater from desalination plants presents better results than seawater due to its higher concentration of chloride ions, allowing it to work at higher redox potential values in order to increase copper dissolution. This manuscript is a bibliographic review in which finally, it is concluded that it is feasible to incorporate wastewater from water desalination plants in heap leaching processes for copper sulfide ores, as long as the cost of transfer from water desalination plants to mining sites can be supported.

Cumulative effects of large-scale desalination on the salinity of semi-enclosed seas

Global desalination capacity is set to increase substantially due to growing water demands globally. The impact of desalination plant discharges on local marine environments is a concern but can be partially mitigated by good plant design to rapidly dilute released brine. For some water bodies with restricted connections to the ocean further concerns have been raised as to whether large-scale desalination risks raising salinity levels of the water body as a whole. Here we assess whether the maximum likely desalination growth by 2050 around the Rea Sea and Gulf of Aqaba could raise salinity levels in these restricted water bodies. The cumulative effect of desalination on salinity levels in the Red Sea will be insignificant compared to natural evaporation. The cumulative effect of desalination on salinity levels in the Gulf of Aqaba may be detectable but within the bounds of natural variability. Careful design and management of the desalination plant outfalls will still be required if the ecological impacts of large-scale desalination are to be manageable.

First large-scale ecological impact study of desalination outfall reveals trade-offs in effects of hypersalinity and hydrodynamics

Desalination is an increasingly common method of meeting potable water demands, but the associated ecological risks are not well understood. Seawater desalination plants discharge large volumes of hypersaline brine directly into the ocean, raising concerns about potential impacts to marine life. In order to reduce impacts of brine, newer desalination outfalls are often fitted with high-pressure diffusers that discharge brine at high velocity into the water column, increasing the mixing and dilution of brine with ocean water. However, there are few published studies of marine impacts of desalination brine, and no well replicated before-after designs. Here we report a six-year study testing for impacts and subsequent recovery of sessile marine invertebrate recruitment near a desalination outfall with high-pressure diffusers. We used a Multiple Before-After-Control-Impact (MBACI) design to test for impacts and recovery at two distances (30 m and 100 m) from a 250 ML/day plant outfall, as well as a gradient design to test the strength of impacts relative to distance from the outfall. The diffusers achieved the target of less than 1 psμ salinity difference to surrounding ambient waters within 100 m of the discharge outfall, but sessile invertebrates were nonetheless impacted. Polychaetes, bryozoans and sponges reduced in cover as far as 100 m from the outfall, while barnacles showed the opposite pattern and were more abundant near the discharging outfall. Ecological impacts were disproportionate to the relatively minor change in salinity (∼1 psμ), suggesting a mechanism other than salinity. We propose that impacts were primarily driven by changes in hydrodynamics caused by the diffusers, such as higher near-bed flow away from the outfall. This is consistent with flow preferences of various taxonomic groups, which differ due to differences in settlement and feeding abilities. High-pressure diffusers designed to reduce impacts of hypersalinity may inadvertently cause impacts through hydrodynamics, leading to a trade-off in minimizing combined salinity and hydrodynamic stress. This study provides the first before-after test of ecological impacts of desalination brine on sessile marine communities, and rare insight into mechanisms behind impacts of a growing form of human disturbance.

Dynamics of lock-release crystalline gravity currents

Coastal and marine environments are impacted by inflows of varying types and chemical compositions. This novel study experimentally investigated the dynamics of a particular type of inflow—crystalline gravity currents (CGC) produced by the lock release of over-saturated brine solutions (i.e., they contain a proportion of suspended salt crystals) into a non-stratified ambient. Such flows may occur from desalination and chemical plant discharges. CGCs were found to show two distinguishing characteristics from normal under-saturated gravity currents (UGC). One was that CGCs have longer slumping distances than UGC while the other was that during the self-similar phase, CGCs have a decreasing trend in their velocities, and the current’s height is no longer constant. These differences result because the CGCs drop crystals onto the bed as they advance. Their flow behaviour was also found to be dependent on the flow head density or local density; whereas, UGC flow is a function of the initial fluid density. This unique study gives a significant insight into crystalline gravity currents showing how they can impact the coastal environments they are encountered in, e.g., the discharge vicinity of desalination and chemical plants.

Ecotoxicological impact assessment of the brine discharges from a desalination plant in the marine waters of the Algerian west coast, using a multibiomarker approach in a limpet, Patella rustica.

The aim of our study is to evaluate the impact of Bousfer desalination plant brine discharges on the Algerian west coast, on a natural population of the marine gastropod mollusc Patella rustica. The effects of a chronic exposure to such discharges are complex to understand due to the combined effects of environmental physico-chemical parameters (e.g., high salinity) and different pollutants that can modulate the physiological responses of this species to stress. In this context, we assessed the biological effects in a marine species P. rustica, by a multibiomarker approach that provided information on the health status of organisms in response to such an environmental stress. We measured biomarkers in the whole soft tissues of limpets as indicators of neurotoxicity (AChE activity), oxidative stress (CAT, SOD, GR, and GPx activities), biotransformation (GST), oxidative damage (LPO through TBARS levels), and genotoxicity (CSP 3-like activity). In parallel, hydrological parameters were measured in the Bay of Oran, at four selected sites: site H considered as a "hotspot," located at Bousfer desalination plant; two other sites E and W, at the east and the west of H respectively; finally, site R "reference" located in Madragh, which is considered as a remote clean site. Our analyses revealed that the activities of antioxidant defense enzymes reached the highest levels in P. rustica collected from site H. The activation of antioxidant defense system in these organisms translated the alteration of their status health, reflecting a level of environmental disruption generated by the desalination plant brine discharges and the high salinity in this area. We also observed that the tissues of limpets collected from site H as well as the two other sites, E and W, had undergone molecular damage, confirmed by the high levels of CSP 3-like activity. This damage resulted from chronic exposure to environmental conditions, potentially genotoxic, due to the desalination plant discharges. The present results indicate the adverse impact of brine effluents from desalination plants on marine fauna and suggest the need for a more consistent approach to environmental management of brine discharges.

Geoenvironmental Impact of Effluents Generated from Al Subiya Power Plant on the Northern Kuwait Bay, State of Kuwait

The present study proposed to assess the geo-environmental impacts of Al Subiya desalination plant discharges in the Arabian Gulf, Kuwait. Most of the power and freshwater needs in the Middle East are met by the desalination of seawater. With approximately 11 million m³ of freshwater being produced each day, the salinity of the seawater along the Gulf coast is increasing. Due to brine discharge into outlet, salinity combined with higher sea surface temperatures was increased is a big environmental challenge. Therefore, in the current study the evaluation of Salinity and conductivity was higher in outlet samples than the inlet. Understanding chemical quality of sediment is important since many pollutants bind strongly to sediment particles and are persistent in the aquatic environment. The chemical and physical make-up of sediment is largely a reflection of upstream and local geology, land use, surface run off and many other complex phenomena. Many persistent compounds have high molecular weight and therefore settle out quickly and are incorporated with other settled organic materials. Since the sediment-water layer is the most reactive layer of the sea bed, changes in the sediment distribution and its physio-chemical characteristics will certainly occur in relation to time and space. In view of this, a distribution map of the sediment is important to understand the changes in composition and nature of contamination in the aquatic environment. This study set out to survey Al Subiya desalination plant inlet and outlet of marine area in Kuwait's Arabian Gulf water and to generate an updated map of the sediments of Kuwait's marine environment, in terms of pollutant factors and the corresponding map of water quality parameters during the survey of one year. The specific objectives were: 1) total organic carbon (TOC), and total petroleum hydrocarbons(TPH) in the sediment collected from selected station, 2) analyze the water quality parameters (pH, Dissolved Oxygen, temperature, salinity, turbidity, conductivity potential) in Al Subiya desalination plant inlet and outlet region, and 3) examine the level of contamination in sediments in terms of size, composition and concentration of different metals and correlate this data with the available physical water quality parameters.

Bioindicators as metrics for environmental monitoring of desalination plant discharges

Development of desalination projects requires simple methodologies and tools for cost-effective and environmentally-sensitive management. Sentinel taxa and biotic indices are easily interpreted in the perspective of environment management. Echinoderms are potential sentinel taxon to gauge the impact produced by brine discharge and the BOPA index is considered an effective tool for monitoring different types of impact. Salinity increase due to desalination brine discharge was evaluated in terms of these two indicators. They reflected the environmental impact and recovery after implementation of a mitigation measure. Echinoderms disappeared at the station closest to the discharge during the years with highest salinity and then recovered their abundance after installation of a diffuser reduced the salinity increase. In the same period, BOPA responded due to the decrease in sensitive amphipods and the increase in tolerant polychaete families when salinities rose. Although salinity changes explained most of the observed variability in both indicators, other abiotic parameters were also significant in explaining this variability.

High salinity tolerance of the Red Sea coral Fungia granulosa under desalination concentrate discharge conditions: an in situ photophysiology experiment

Seawater reverse osmosis desalination concentrate may have chronic/acute impacts on the marine ecosystems in the near-field area of the discharge. Environmental impact of the desalination plant discharge is supposedly site- and volumetric specific, and also depends on the salinity tolerance of the organisms inhabiting the water column in and around a discharge environment. Scientific studies that aim to understand possible impacts of elevated salinity levels are important to assess detrimental effects to organisms, especially for species with no mechanism of osmoregulation, e.g. presumably corals. Previous studies on corals indicate sensitivity towards hypo- and hyper-saline environments with small changes in salinity already affecting coral physiology. In order to evaluate sensitivity of Red Sea corals to increase salinity levels, we conducted a long-term (29 days) in situ salinity tolerance transect study at an offshore seawater reverse osmosis discharge on the coral Fungia granulosa. While we measured a pronounced increase in salinity and temperature at the direct outlet of the discharge structure, effects were indistinguishable from the surrounding environment at a distance of 5 m. Interestingly, corals were not affected by varying salinity levels as indicated by measurement of the photosynthetic efficiency. Similarly, cultured coral symbionts of the genus Symbiodinium displayed remarkable tolerance levels in regard to hypo- and hypersaline treatments. Our data suggest that increased salinity and temperature levels from discharge outlets wear off quickly in the surrounding environment. Furthermore, Fungia granulosa seem to tolerate levels of salinity that are distinctively higher than reported for other corals previously. It remains to be determined whether Red Sea corals in general display increased salinity tolerance, and whether this is related to prevailing levels of high(er) salinity in the Red Sea in comparison to other oceans.

Marine monitoring surveys for desalination plants—a critical review

Environmental impact assessment (EIA) studies are standard practice and a regulatory requirement for most new desalination projects today. However, most of the EIA studies are limited to predictive information; that is, they gather information on the project and the project’s environment before project implementation to make predictions about likely impacts. The EIAs may involve comprehensive studies, such as field monitoring, laboratory toxicity testing, and modeling studies. Consequently, the “surprising paucity of useful experimental data, either from laboratory tests or from field monitoring studies”, which was observed by the US National Research Council in 2008, has been gradually decreasing. However, there is still a long-term research need on the site-specific effects of desalination plants after project commissioning has taken place. A main challenge of field research is the adequate design of the monitoring studies, which have to adequately distinguish the effects of the desalination project from natural processes over long periods of time. The existing monitoring studies have so far used a wide range of approaches and methods to investigate the environmental impacts of desalination plant discharges. Shortfalls are often that they are limited in scope, short-term, or localized. In essence, many studies fall short of recognizing the potentially synergetic effects of the single waste components of the discharges on marine organisms and the complexity of the potential responses by the ecosystem. While the possible risk of damage arising from the concentrate discharge to the marine environment in close proximity to the outfall is at hand, no conclusive evidence can yet be provided concerning the long-term impacts of desalination plant discharges, let alone the cumulative impacts on certain sea areas. This paper conducts a critical review of existing monitoring programs for desalination plants. Shortcomings of current practices are identified and relevant aspects to the design of marine monitoring programs outlined, including the scope of the studies as well as their scientific requirements.

Comparing four mixing zone models with brine discharge measurements from a reverse osmosis desalination plant in Spain

Nuevo Canal de Cartagena (Spain) desalination plants discharge hypersaline effluent through a submarine outfall pipeline, creating a negatively buoyant brine jet. Many near-field mixing models are used in the prediction and management of brine discharges, but they have rarely been compared with field salinity measurements obtained directly inside the brine jet. Two divers obtained these field measurements and compared them with CORMIX1, CORJET, MEDVSA and UM3 mixing zone model predictions. In general, each model was quite conservative in its results, except UM3, whose prediction presented the best approximation to measured data. It is concluded that direct field measurements should be essential when testing the accuracy of current models or developing new near-field mixing models.

Metal Concentrations in Organs of the Clam Amiantis umbonella and Their Use in Monitoring Metal Contamination of Coastal Sediments

The aim of this study was to evaluate the use of metal concentrations in clam organs to monitor metal contamination in coastal sediments. The concentrations of Cd, Cr, Cu, Hg, Ni, Pb, V, and Zn were measured in the kidneys, gonads, mantles, gills, digestive gland, and hearts of the infaunal clam Amiantis umbonella collected from a contaminated site near desalination and power plant discharges, and a reference site in Kuwait Bay. Metal concentrations in sediment and sediment pore water were also measured at the collection sites of individual clams at the contaminated site. The concentrations of all metals in all organs (except Zn in the digestive gland) were significantly higher in clams from the contaminated site than from the reference site. Metal concentrations in several organs in A. umbonella from the contaminated site were correlated with those in the sediments and pore waters to which they were exposed. However, fresh weights of gonads, gills, and mantles were significantly lower in clams from the contaminated site compared to the reference site, indicating that the observed elevated concentrations of metals in the organs of clams from the contaminated site largely reflect lower organ weights, rather than higher metal loads, and that these organs in A. umbonella and perhaps other clams are not appropriate for use as biomonitors of metal contamination. Metal concentrations in clam kidneys showed a wide dynamic range with respect to environmental contamination and kidney weight was not variable. Therefore, metal concentrations in clam kidneys provide a reliable biomonitor of contaminant metals in coastal marine sediments.

Mixing zone regulation for effluent discharges into EU waters

Environmental standards and their implementation in different countries are reviewed for point source discharges into surface waters. The paper focuses on the analysis of existing mixing zone regulations and recommends procedures to develop and manage mixing zone definitions as required by recent amendments of the ‘combined approach' of the European Community water framework directive. The review shows that only a few mixing zone regulations exist in the European Union member countries, and that some effluent types, such as desalination brine discharges, and some discharge technologies, such as river diffusers, are not yet considered. The paper discusses those two issues in detail. First, by analysing desalination plant discharge characteristics and recommending mixing zone regulations for such multi-component and multi-process discharges. Second, by presenting river diffuser discharge technologies and procedures for demonstrating compliance of discharges that employ these technologies.

Desalination plant discharge calculator

The impacts of a desalination plant discharge on the marine environment depend on the physical and chemical properties of the desalination plant reject streams, and the susceptibility of coastal ecosystems to these discharges depending on their hydrographical and biological features. Therefore, a good knowledge of both the effluent properties and the receiving environments is required in order to evaluate the potential impacts of desalination plants on the marine environment. The brine flows are considerably large, generally up to 40% (for membrane based technologies, like reverse osmosis, RO) and up to 90% (for thermal technologies, like multi-stage-flash, MSF, including cooling water) of the intake flowrate. Thus either almost as large or even considerably larger flows than the required freshwater water flow. Salinity and temperature directly influence the density of the effluent. The various density differences between the brine and the receiving water represented by the buoyancy flux causes different flow characteristics of the discharge. The dense RO effluent flow has the tendency to fall as negatively buoyant plume and spread as a density current on the sea-floor. The effluent from thermal desalination plants is distinguished by a neutral to positive buoyant flux causing the plume to rise and to spread on the sea-surface. This article describes a discharge calculator to compute the effluent properties (i.e. density, flow, temperature, salinity, etc.) and substance concentrations at the discharge point. It allows the input of up to three different effluent types with different individual flows, properties and constituents, which are then merged at the discharge point. This allows the consideration of desalination effluents be blended with other effluents like treated wastewater or cooling waters from the process itself or a cogenerating power plant. Furthermore, the calculator characterizes the effluent properties and computes basic discharge characteristics by comparing the effluent properties with ambient characteristics. In addition, the calculater includes simple approaches to compute estimates regarding the initial mixing. Results of computations for different case-studies demonstrate the potential of the calculator to estimate the order of magnitude of expected temperature, salinity or substance concentration at the discharge point and its surroundings. It allows furthermore to analyze the need for advanced discharge technologies which aim for enhanced effluent dispersion in the receiving environment and adequate discharge siting to avoid pollutant accumulation and to protect sensitive regions. It also allows to interpret the probability of interaction with the intake.

Salt production from brine of desalination plant discharge

Desalination in the Gulf Cooperation Council (GCC) countries is a growing industry to match the requirement of population growth and the high water demand. This activity however, may generate an environmental impact due to discharge of the brine into the sea and to the chemical utilized during the process operation. The brine can potentially affect marine life and ecology in the proximity of the plant discharge. The seawater salinity is increasing due to the high evaporation rate and to the number of desalination plants growth in the region. One possibility is to reuse brine from desalination plants in a salt plant to produce sodium chloride required for exploration as well as in oil refining process; this should be done in order to protect the environment and to produce a commercial and utilizable salt with a competitive price. The paper presents a technical and economic study to reuse the brine to try to reduce the negative impact of the brine discharge.

Salinity tolerance evaluation methodology for desalination plant discharge

Seawater desalination plants generate concentrate (brine) which typically has 1.5 to 2 times higher total dissolved solids concentration (salinity) than that of the ambient seawater. When returned to the ocean without dilution, this concentrate may have a negative impact on the aquatic environment in the area of the discharge. The environmental impact of the desalination plant discharge is very site-specific and depends to a great extent on the salinity tolerance of the specific marine organisms inhabiting the water column and benthic environment influenced by the discharge. This work presents methodology that allows establishing the site-specific maximum level of salinity concentration (salinity tolerance threshold) at which marine organisms not only survive, but can also grow and reproduce normally. The described method was used successfully for the permitting of the concentrate ocean discharge of two large seawater desalination projects in California — the 189,000 m3/d (50 MGD) Carlsbad and Huntington Beach desalination plants.

Modelling and environmentally sound management of brine discharges from desalination plants

Sea water desalination plants discharge a concentrated brine effluent into coastal waters. Modern, large capacity plants require submerged discharges, in form of a negatively buoyant jet, that ensure a high dilution in order to minimize harmful impacts on the marine environment. Existing design practice favors a steep discharge angle of 60° above horizontal that is based on very limited laboratory data on dilutions at the level of maximum rise. However, examination of more recent laboratory data and the parametric application of CorJet, a jet integral model within the CORMIX expert system suggest that flatter discharge angles of about 30° to 45° above horizontal may have considerable design advantages. These relate to better dilution levels at the impingement location, especially if bottom slope on port height are taken into account, better offshore transport of the mixed effluent during weak ambient current conditions, and the ability to locate in more shallow water near-shore.

Improved Discharge Configurations for Brine Effluents from Desalination Plants

Sea water desalination plants discharge a concentrated brine effluent into coastal waters. Modern, large capacity plants require submerged discharges, in the form of a negatively buoyant jet, that ensure a high dilution in order to minimize harmful impacts on the marine environment. Existing design practice favors a steep discharge angle of 60° above horizontal, a practice based on limited and outdated laboratory data for dilutions at the level of maximum rise. Examination of more recent laboratory data and the parametric application of a jet integral model suggest that flatter discharge angles of about 30-45° above horizontal may have considerable design advantages. These relate to better dilution levels at the impingement location, especially if bottom slope and port height are taken into account, there is better offshore transport of the mixed effluent during weak ambient current conditions, and there is the ability to locate in more shallow water near shore.