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Performance indicators and ranking methods are effective tools for assessing the environmental impact of emerging technologies and comparing the operational efficiencies of different processes. Desalination of seawater, which is vital for solving the water shortage in the Arabian Gulf region, should be assessed due to its adverse environmental impacts on the shallow and closed Gulf basin. The main objective of the current work is to develop and implement an environmental assessment methodology capable of ranking alternative desalination processes and technologies based on their environmental performance. The proposed methodology starts with identification of relevant indicators and uses the relative ranking of desalination plants together with an aggregated environmental index. The assessment approach was tested on selected desalination plants in the Arabian Gulf region. The results showed that the ranking methods are effective in aggregating the influence of individual indicators to produce a numerical value that indicates the rank of studied desalination plants with respect to their environmental impact. [ABSTRACT FROM PUBLISHER]

Discharge from the desalination plants of Kuwait returns brines of high salinity to the Gulf that contain other contaminants, such as chlorine or chromium, impacting the environment of the coastal region. Conversely, wastewater discharges to the Gulf have low salinity but may drive eutrophication of coastal waters. Pressure retarded osmosis (PRO) is a promising source of renewable energy and an emerging membrane-based technology for recovering energy from concentration differences between water streams. The proposed work examines the feasibility of using PRO to generate energy from wastewater and desalination plants in Kuwait by calculating the power density using a PRO zero-dimensional model. The model accounts for concentration polarization (CP) and salt leakage (B ′ ) effects to produce realistic results. The effects of CP and (B ′ )on the power density at varying applied pressures and varying concentration differences between the feed and draw solutions are studied. Case studies on the potential re-use of treated wastewater effluent (TWE) and brine reject streams from three wastewater treatment plants (WWTPs) in Kuwait are discussed and compared to determine the maximum power generated from each of the WWTPs. The power densities generated from wastewater treatment (WWT) plants in Al-Jahra city, Um Al-Haiman city and Al-Riqqa were studied. The power density from Al-Haiman WWTP (18.73 W/m 2 ) is the highest compared to those of the other two WWTPs. The limits of the zero-dimensional model are also presented in this study. The PRO power density (W) was studied as a function of hydraulic pressure (ΔP) at different feed and draw solution concentrations. At higher draw solution concentrations (85 g/L NaCl), the power densities were higher. This increase in power density values was attributed to the higher driving forces acting in the system. Concentration polarization (CP) and salt leakage (B ′ ) reduce the driving forces across the membrane. The power density values (W) were smallest in the presence of both CP and(B ′ ). The effects of CP and (B ′ ) vary depending on the concentrations of the draw and feed solutions. [ABSTRACT FROM AUTHOR]

Confined plunging jets are investigated as potential outfalls for the discharge of desalination brine. Compared to offshore submerged outfalls that rely on momentum to induce mixing, plunging jets released above the water surface utilize both momentum and negative buoyancy. Plunging jets also introduce air into the water column, which can reduce the possibility of hypoxic zones. In contrast to unconfined plunging jets, confined plunging jets include a confining tube, or downcomer, around the jet, which increases the penetration depth of the bubbles and can provide better aeration. However, the presence of this downcomer can hinder mixing with surrounding water. Therefore, laboratory measurements of dilution are reported here and compared to the dilution of unconfined plunging jets. In addition, qualitative observations of bubble penetration depth are also used to discuss aeration potential. For designs that increase the bubble penetration depth as compared to unconfined plunging jets, results show that dilution decreases as the depth of the downcomer is increased. However, it is shown that confined plunging jets can be designed with a short downcomer to provide higher dilution than unconfined jets. The effect of the diameter of downcomer on dilution is also investigated and a non-monotonic effect is observed. [ABSTRACT FROM AUTHOR]

The potential of producing salt and low salinity water by treating synthetic brine was investigated in a pilot-scale electrodialysis-evaporator hybrid system as part of brine management. An electrodialyzer with 25 cell pairs of monovalent selective anion exchange membranes (AEMs) and monovalent selective cation exchange membranes (CEMs) were used. Effect of three different current densities (300 to 500 A/m2) and two different flowrates (400 L/h and 450 L/h) on brine treatment were evaluated in the current study. The results indicated that the aforementioned membranes were efficient in separating monovalent ions over divalent ions. Moreover, higher current density operation was favoured during the electrodialysis (ED) operation as the operation time for producing salt was shorter. Flowrate is a crucial parameter for the operation of the ED system, where higher flowrate (by 12.5%) reduced the operation time (by 30 min), reduced energy consumption (by 32%) and reduced system resistance (by 32.42%) leading to an increase in current efficiency (by 31.4%). The concentrated brine effluent from ED was fed to an evaporator to produce coarse salt with 84.75% salt recovery and low salinity water of 1526 ppm. Thus, ED-evaporator hybrid system was found to be a good option to treat reject brine from desalination plants. • An electrodialysis-evaporator hybrid system was employed for brine management. • A multi-stage batch series method was carried out using monovalent membranes. • High current densities of 300–500 A/m2 and two flowrates were used in this study. • Coarse salt with 84.75% recovery was produced after the evaporation process. • Advanced SEM-EDX analysis was used to detect the fouling in the end CEM. [ABSTRACT FROM AUTHOR]

Laboratory experiments were conducted to measure entrained air bubble penetration depth and dilution of a dense vertical unconfined plunging jet to evaluate its performance as an outfall to dilute brine from desalination plants as well as a means to aerate water column. Experiments involved neutrally buoyant or dense plunging jets discharging in quiescent receiving water. The density difference between effluent and receiving water, the plunging jet length (height above water surface), and the receiving water salinity were varied in the experiments. Observed penetration depth for neutrally buoyant jets was somewhat greater than previously reported, and increased modestly with jet density. Increasing density also resulted in an increasing number of fine bubbles descending together with the dense plume. These observations can help guide the design of plunging jets to mitigate anoxic conditions in the water column when brine is introduced to a receiving water body, as with seawater desalination. [ABSTRACT FROM AUTHOR]

Brine discharges from desalination plants into low-flushing water bodies are challenging from the point of view of dilution, because of the possibility of background buildup effects that decrease the overall achievable dilution. To illustrate the background buildup effect, this paper uses the Arabian (Persian) Gulf, a shallow, reverse tidal estuary with only one outlet available for exchange flow. While desalination does not significantly affect the long-term average Gulf-wide salinity, due to the mitigating effect of the Indian Ocean Surface Water inflow, its resulting elevated salinities, as well as elevated concentrations of possible contaminants (such as heavy metals and organophosphates), can affect marine environments on a local and regional scale. To analyze the potential effect of background salinity buildup on dilutions achievable from discharge locations in the northern Gulf, a 3-dimensional hydrodynamic model (Delft3D) was used to simulate brine discharges from a single hypothetical source location along the Kuwaiti shoreline, about 900 km from the Strait of Hormuz. Using nested grids with a horizontal resolution, comparable to a local tidal excursion (250 m), far field dilutions of about 28 were computed for this discharge location. With this far field dilution, to achieve a total dilution of 20, the near field dilution (achievable using a submerged diffuser) would need to be increased to approximately 70. Conversely, the background build-up means that a near field dilution of 20 yields a total dilution of only about 12. [ABSTRACT FROM AUTHOR]