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Desalting brines from Reverse Osmosis (RO) plants is one of the most promising applications of Membrane Distillation (MD) systems. The development of accurate models to predict MD system performances plays a significant role in the design of this kind of industrial applications. In this paper, a commercial-scale Permeate-Gap Membrane Distillation (PGMD) module was modelled by means of two different approaches: Response Surface Methodology (RSM) and Artificial Neural Networks (ANN). Condenser inlet temperature, evaporator inlet temperature, feed flow rate and feed water salt concentration were selected as inputs of the model, while permeate flux and Specific Thermal Energy Consumption (STEC) were chosen as responses. The prediction abilities of both RSM and ANN models were compared with further experimental data by using the Analysis of Variance (ANOVA) and the Root Mean Squared Error (RMSE). The results show that the ANN model is able to predict in a more precise way the behaviour of the module for the whole range of input variables. Thus, ANN model was used to find the optimal operating conditions, for the module operating at feed water salinity of 70 and 105 g/L, concentrations that can be reached when desalting RO brines.

This work presents the evaluation of an innovative system based on vacuum multi-effect membrane distillation modules (V-MEMD) for seawater desalination at pilot scale. This four-effect unit introduces a remarkable modification from previous V-MEMD systems, consisting of the use of the seawater feed flow as cooling in the condenser, rather than a separate circuit. Preheating the feed in the condenser improved heat efficiency (maximum gained output ratio obtained for seawater was 3.2). Maximum distillate fluxes reached 8.5 l h−1 m−2 for hot feed temperature 75 °C and feed flow rate 150 l h−1. Increasing both parameters to raise the productivity was hindered by the inability of the condenser to cope with all the steam generated in previous effects, resulting in overheating and overpressure. Furthermore, a loss of 40% of distillate production was measured due to the increase of seawater cooling temperature by 8 °C along the year. Finally, it was observed that scaling reduced distillate production up to 50%. Acid cleaning successfully removed scaling and restored the performance. Subsequently, the use of an antiscalant as a pre-treatment was sufficient to prevent it.

In this paper, a commercial spiral wound PGMD module was modeled and optimized for seawater desalination using Response Surface Methodology (RSM). Permeate flux (P flux ) and specific thermal energy consumption (STEC) were the main performance parameters to optimize, while evaporator inlet temperature (T evap ), condenser inlet temperature (T cond ) and feed flow rate (F) were the three operating parameters chosen. Analysis of variance (ANOVA) was used to evaluate statistically the response surface models. According to the study, T evap had the strongest effect on P flux and STEC, increasing the former and decreasing the latter, F increased both responses, and T cond had a weak effect on P flux and practically none on STEC. The models were validated with further experimental data and a good correlation between experimental and predicted values of the responses was obtained for P flux and STEC respectively. An optimization was performed to determine the operating conditions that produce a maximum value of P flux and a minimum value of STEC simultaneously. The result of the multiple responses optimization using desirability function was a maximum P flux of 2.66 l/h·m 2 and a minimum STEC of 255.8 kWh/m 3 .

This work presents the results of the techno-economic analysis of a proposed 100 m3 day− 1 desalination plant based on existing plate and frame MD technology coupled with a static solar collector field as main heat supply. The experimental results of one commercial and two pre-commercial MD modules characterized previously under real operational conditions were used. Three different cost-effective solar technologies (evacuated tube collectors (ETCs), flat plate collectors (FPCs) and compound parabolic collectors (CPCs)) were considered for the analysis and the results were compared to a fossil source. For the dimensioning of the solar field, meteorological data from Almeria (South-Spain) where the experimental campaign took place were selected. A thorough economical assessment was performed to calculate the cost of water (WPC) for the different considered scenarios. The best results obtained show a WPC in the range of 10–11.30 € m− 3 for the combination of the most efficient MD module and solar collector. The fossil-driven option showed a similar (i.e. 7.19 € m− 3) yet lower WPC. Although the MD technology here analyzed is in an early stage of development, the results obtained suggest solar MD can be already competitive with PV-RO and PV-ER according to reported data for similar capacities (~ 100 m3 day− 1).

The combination of desalination with concentrated solar power (CSP) plants (CSP + D) is considered as the most realistic opportunity for the development of large-scale desalination with solar energy. The availability of solar power and waste heat in CSP plants offers possibilities for both reverse osmosis (RO) and thermal desalination systems. In the case of RO the combination can be done directly by transporting the electricity. In the case of thermal desalination technologies there are different alternatives for coupling with CSP plants which can offer advantages with respect to the CSP + RO combination such as the reduction of the cooling needs of the power cycle. A techno-economic analysis of different schemes of multi-effect distillation (MED) systems coupled with CSP plants is presented here and compared to the CSP + RO option. The study is done using validated models of MED plants and considering the three conventional cooling methods available in CSP plants: dry cooling, once-through and wet cooling. The analysis is performed using operating conditions of real plants. The comparisons are done for the two main regions where the cogeneration of electricity and fresh water using CSP + D is proposed: the Mediterranean basin and the Arabian Gulf.

© 2014 . A dual stage PRO process is proposed here for power generation using osmotic energy. The process is able to handle a wide range of feed water salinities with different pretreatment requirements in order to reduce the membrane fouling problems. In the current study, the salinity gradient resource consisted of seawater at standard TDS, 35. g/L, while the first stage feed water was brackish water or fresh water and the second stage feed water was wastewater effluent. The diluted seawater from the first stage of PRO process was the draw solution in the second stage of PRO process. The performance of dual stage PRO process was evaluated for a number of brackish water salinities ranged from 1. g/L to 5. g/L. The TDS of wastewater and freshwater was assumed 0.2. g/L. The results showed that a better PRO performance was achieved when the brackish water and the wastewater were introduced in the first stage and the second stage respectively. In case when wastewater and brackish water were introduced in the first and second stage respectively there was about 28% decrease in the second stage permeate flow. The results also showed a decrease in the first stage permeate flow with increasing the feed salinity but the second stage permeate flow increased with increasing the feed salinity. Furthermore the results showed that the first stage maximum power density was achieved at δP=. δπ/2 while the second stage maximum power density was achieved at δP=. δπ/1.5. Unlike the conventional PRO process, it has been found that the impact of feed salinity increase on the performance of dual stage PRO process was insignificant. Finally, the power generation in the dual stage PRO process was higher than that in the conventional PRO process. The difference was equal to the entire amount of power generated in the second stage of PRO process.

Forward Osmosis (FO) has many applications in water and wastewater treatment and seawater desalination. In this paper, the FO was suggested for seawater pretreatment to the thermal desalination processes such as Multi Stage Flashing (MSF). The integrated FO–MSF hybrid system was designed to reduce the cost of desalination in which the brine reject from MSF was recycled and reused as a draw solution in the FO process. A simple model was suggested here to estimate water flux and power consumption in the FO process and compared with Nanofiltration (NF) process which was previously used in seawater softening. The simulation results showed that for feed salinities between 32,000 mg/L and 50,000 mg/L the recovery rate in the NF was higher than that in the FO. It is also found that the water permeability and specific power consumption was higher in the NF than that in the FO. However, power consumption in the FO wasn't affected by the feed salinity while it increased with feed salinity in NF. Therefore, the FO process has the potential to replace the NF seawater pretreatment for thermal desalination.

A steady-state mathematical model of a vertically stacked forward feed multi-effect distillation (MED) plant has been carried out using a number of simplifying assumptions. The model has been developed taking into consideration the same design and operational characteristics as the pilot MED plant at Plataforma Solar de Almeria (PSA), in the southeast of Spain. It is a forward feed MED plant with preheaters, which uses low steam temperature coming from a parabolic-trough solar collector field as the thermal energy source. The pilot plant has a special distillate distribution for increased energy recovery which has also been taken into account in the model. This model is simple to implement and suitable for its use in optimization of water production in power and water cogeneration systems. The results of the model have been compared with the experimental data of the pilot plant showing a maximum prediction error of 9%.

The combination of Forward Osmosis (FO) and Reverse Osmosis (RO) was evaluated for seawater desalination. RO process was suggested for the draw solution regeneration because of its high efficiency and applicability for a wide range of ionic solution treatments. Two different salts, NaCl and MgCl2, were used as a draw solution. The performance of FO and RO regeneration processes was simulated using pre-developed software. A comparison between the RO and FO-RO processes was carried out. The simulation results showed that the total power consumption in the RO was lower than that in the FO-RO process. But, the difference in total power consumption between the RO and 0.65mol MgCl2 FO-RO processes was insignificant. The results also showed that the power consumption in the FO process was only 2%-4% of the total power consumption in the FO-RO process. However, the difference in total power consumption between the RO process and the FO-RO process decreased with a higher seawater salinity. In the FO-RO process, the results showed that the permeate TDS was increased with increasing the concentration of draw solution. The lowest permeate TDS was achieved in the 0.65mol MgCl2 FO-RO process and it was attributed to the high rejection rate of MgCl2 by the RO regeneration unit. © 2014 Elsevier B.V.

Integrated power and desalination plants (IPDP) may provide a key solution for the pressing freshwater deficit and energy problems in many regions of the world. The current study investigates the potential of low-temperature multi-effect distillation (LT-MED) and thermal vapor compression multi-effect distillation (TVC-MED) coupled with a concentrating solar power (CSP) plant, taking also into account a reverse osmosis (RO) unit connected to the same power plant. The thermodynamic performance of the proposed schemes of IPDP has been evaluated by the assessment of the net output thermal capacity and the net power cycle efficiency of the different configurations, together with the estimation of the size of the solar field required to provide the corresponding thermal capacity. The results show that the combination with LT-MED is more efficient thermodynamically than with TVC-MED. Also, the CSP plant coupled with TVC-MED is more cost-effective than the independent processes because it requires a smaller solar field. The integration of a MED plant reduces the cooling requirements of a CSP power plant but the CSP + RO combination has a better thermodynamic efficiency. However, the difference with respect to CSP + LT-MED is small, so the latter can be more convenient in some cases.

Watergy project is funded by the European Community’s Vth Framework in its Energy, Environment and Sustainable Development programme. It consists of the development of a humid air solar collector system that follows the principle of a closed two phase thermosyphon. A combination of evaporation and condensation allows to use solar thermal energy in a much more efficient way. The main advantage is not only the reduction of costs in space cooling and heating, but the possibility of water purification, as the system can be fed with low quality water to obtain distilled water. The decentralization of heat and water supply opens the possibility of residential areas where greenhouses fed with low quality water (grey water and brackish water) could be used to produce distilled water as well as heat and fruits. The project contemplates the development of two prototypes: one application for arid climates in Southern Europe with an emphasis on water production in the context of greenhouse horticulture, and another for temperate Central European climate focused on heat and water production for sustainable architecture.

In desalination, similarly with other industries, the cost of the final product is one of the most important criteria that define the commercial success of a specific technology. Therefore, when new projects are planned or new technologies are proposed, the analysis of the expected costs attracts a lot of attention and is compared to (perceived) costs of state-of-the-art desalination or costs of alternative fresh water supply options. This comparison only makes sense if the cost assessment methodologies are based on the same principles and use common assumptions. This paper assesses: (i) the methodologies used to calculate the water cost; (ii) the boundary conditions and (iii) the input data and assumptions. It has been found that most papers in the literature use suitable equations and boundary conditions. Also certain elements like land costs are ignored, but in most cases this is duly acknowledged and justified. However, the quality of the input data for the hardware costs, the operating costs, and the financial parameters are not always appropriate. Guidance for the methodology, data and assumptions that should be used is provided depending on the purpose for which the cost of the desalinated water is calculated.