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© 2018 Desalination Publications. All rights reserved. A dual stage PRO process has been proposed for power generation from a salinity gradient across a semi-permeable membrane. Both closed-loop and open-loop dual stage PRO system were evaluated using 2 M NaCl and Dead Sea as draw solutions, whereas the feed solution was either fresh water or seawater. The impact of feed salinity gradient resource and feed pressure on the net power generation and water flux were evaluated. The results showed that power density in stage one reached a maximum amount at ΔP = p/2, but the maximum net power generation occurred at ΔP = p/2. This result was mainly attributed to the variation of net driving pressure in stage one and two of the PRO process. The dual stage PRO process was found to perform better at high osmotic pressure gradient across the PRO membrane, for example when Dead Sea brine or highly concentrated NaCl was the draw solution. Total power generation in the dual stage PRO process was up to 40% higher than that in the conventional PRO process. This outcome was achieved through harvesting the rest of the energy remaining in the diluted draw solution. Therefore, a dual stage PRO process has the potential of maximizing power generation from a salinity gradient resource.

A 72 m3/d pilot low-temperature multi-effect distillation plant located at the Plataforma Solar de Almeria has been experimentally characterized at steady state to study the influence of the variation in certain parameters that control the process (the hot water inlet temperature as external thermal energy source and the last effect vapor temperature) on the distillate production, the thermal consumption, and the thermal energy efficiency of the plant. Results allowed characterizing the increase in the water production and the thermal consumption with the increase in the hot water inlet temperature and with the decrease in the last effect vapor temperature. The performance ratio reached its maximum when the last effect vapor temperature ranged from 25 to 35°C, since the temperature difference between effects was lower. The preliminary characterization of this plant provides useful experimental information for design criteria and for the analysis of control strategies of other large-scale MED plant...

© 2016 Balaban Desalination Publications. All rights reserved. Novel desalination approaches are required to provide both drinking and agricultural water as there is ever increasing stress upon precious freshwater resources. It was our hypothesis that a modified Forward Osmosis (FO) process had the potential for production of irrigation water comprising of appropriate concentrations of fertilizers from a seawater feed. Four agents, KNO3, Na2SO4, CaNO3, and MgCl2, plus 35 g/L seawater were used as the draw and feed solutions of the FO process. Net Driving Pressure in the FO process was manipulated either by increasing the concentration of draw solution (FO process) or by increasing feed pressure (Pressure Assisted FO (PAFO) process). A series of nanofiltration (NF) and reverse osmosis (RO) membranes were used for the regeneration of draw solution. The results suggested that a PAFO process was more energy efficient than simple FO, provided the energy relating to the brine flow from the NF/RO membrane for pressurizing the feed solution of PAFO process was used. Furthermore, this study suggested using a mixture of a primary draw solution, MgCl2, and a secondary draw solution, KNO3, for NO3 supply into the irrigation water was preferable. As such, MgCl2 provided the driving force for fresh water extraction while KNO3 was the source of fertilizer in the irrigation water. Results showed that water quality provided by application of a MgCl2 + KNO3 draw solution was better than that from KNO3 or Ca(NO3)2. The concentrations of NO3 and SO4 in irrigation water were within recommended levels when the diluted draw solution was regenerated by a dual stage low-pressure RO process.

Experiments were conducted with a commercial membrane distillation module, which has an air-gap membrane distillation (AGMD) and spiral-wound configuration. Tests were performed simulating the salinity and temperature of the water using as a case study the Albian aquifer in Algeria. Solar thermal energy from a field of stationary flat-plate solar collectors was supplied to the module. The total productivity of the AGMD system was analyzed for different operational conditions and compared with that from the RO system. The effect of brackish water temperature on the energy consumption was scrutinized, and the energy requirements assessed toward the design of a pilot unit for decentralized autonomous solar desalination. Results showed that for producing a higher volume of distillate, module with less surface area is better. Also, it was found that recovery ratio increases linearly with the temperature difference in both modules. The maximum value was 6% for the highest feed flow rate operated in modu...

A dual stage pressure retarded osmosis (PRO) process was investigated for power generation using different types of membranes. Polyamide (PA) and cellulose triacetate (CTA) membranes were used in the first and second stage of the PRO process to improve the process performance due to the high water permeability of PA membranes. A comparison between dual stage PA–CTA and CTA–CTA membrane systems were carried out using seawater as a draw solution, while fresh water and wastewater effluent were the feed solution in the first and second stage of the process. The impact of draw solution flow rate on the process performance was evaluated. The performance of first and second stage of the PRO process increased by 11.5 and 28.6%, respectively, when the draw solution flow rate increased by a factor of 2.5. In return, there was a negligible increase in the total specific power consumption of the PRO process. In general, power consumption of the dual stage PRO process was as low as 0.3 kWh/m3. Furthermore, the...

Two-stage forward osmosis (FO)–reverse osmosis (RO)/BWRO and conventional RO/BWRO processes were evaluated for saline water treatment. Three different salts, NaCl, MgCl2 and MgSO4, were used as a draw solution. The performance of FO, RO and BWRO regeneration processes was simulated using predeveloped software. The simulation results showed that the water and solute flux across the FO membrane decreased with increasing the FO recovery rate. The highest water flux was in case of 1.2 mol NaCl draw solution for seawater desalination. The total power consumption for seawater desalination was lower in the RO process than in the FO–RO process. However, as the RO recovery rate increased, the difference in total power consumption between the conventional RO process and 0.65 mol MgCl2 FO–RO processes was insignificant. In case of brackish water desalination, the lowest specific power consumption and permeate TDS were in case of the conventional BWRO process and then followed by 0.32 mol MgSO4, 0.22 mol MgCl...

Together with desalination, reuse of wastewater is considered as a solution to mitigate the water deficit in many areas. Membrane distillation (MD) is a technology increasingly proposed for desalination and water treatment. The process is supposed to produce pure distillate, and this is what this paper evaluates. Biologically contaminated water was used in a commercial prototype of spiral-wound liquid-gap MD coupled with solar thermal energy to assess the suitability of the process for removing pathogens. Tests were done during several hours for different operating conditions. The produced distillate, the rejected concentrated solution and the feed water were monitored through time and samples were taken for microbiological analysis. Results proved the efficiency of solar MD to produce a contaminant-free distillate when Escherichia coli, Fusarium solani and Clostridium sp spores were present in the feed water. Furthermore, in the first two cases the population of biological contaminants in the con...

The use of solar energy to feed the MD desalination process is being evaluated at Plataforma Solar de Almeria, the largest European facility for solar energy research, located in SE Spain. A test bed for the evaluation of membrane distillation modules is under operation coupled to a field of static solar collectors. Different commercial modules and real-scale prototypes are tested in continuous operation and coupled with a solar thermal source, in order to obtain data in conditions closer to real applications than the tests performed at laboratory scale. This particular study shows an evaluation of two different modules using spiral-wound membranes, one with a liquid-gap configuration (built by Solar Spring) and the other with an air-gap configuration (built by Aquastill). An assessment of the influence of the operational parameters in the performance was done within the allowed ranges of operation of each prototype, with special attention to the temperatures and the feed flow rate. Also, the infl...

The development of society is strongly dependent on water and electricity. There is an increasing water and energy demand driven by population growth and rising industrial and agricultural production. The combination of concentrated solar power (CSP) and desalination processes has a huge potential for producing both energy and water in arid regions suffering from fresh water scarcity and facing the current energy challenge. One of the regions is Middle East and North Africa (MENA), where plans are currently under discussion to make possible large CSP plants developments. The integration of desalination (CSP+D) into solar power plants could make CSP technology even more attractive in such regions. The focus of this study is thermodynamic characterization and an economic evaluation of different configurations for coupling parabolic trough solar power plants and desalination facilities at a MENA location in Egypt chosen as reference for its Southern coast (Port Safaga). The desalination technologies...

In this work a steady-state model is developed of an MED plant. Its development and validation have been carried out by experimental data obtained from an MED pilot plant located at the Plataforma Solar de Almeria (PSA), in the southeast of Spain. It is a vertical arrangement forward-feed MED plant with preheaters, which uses hot water as the thermal energy source. In order to run the model, a series of parametric equations have been determined for the following variables: the overall heat transfer coefficient for the first effect (U h), the overall heat transfer coefficient for the preheaters (U p(i)), the vapor temperature inside the first effect (Tv (1)), and the cooling seawater outlet temperature (T cwout). They have been obtained from a three-level factorial experimental design (3k), performing a total of 81 experiments (34). The results obtained showed a good fit to the estimated models for the response variables.