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ab s t r ac tThe specific energy consumption (SEC) of pressure-driven liquid-phase membrane processes, in particular the reverse osmosis (RO) process, has usually been estimated using a phenomenological approach, which does not explicitly consider the membrane properties and operating parameters. This paper presents a new analytical approach that has been derived, from a well-established theory, to estimate the SEC and to quantify the effect of membrane properties; namely, membrane permeability and surface area as well as the effect of process parameters such as feed pressure, recovery rate, membrane element permeate rate, and feed osmotic pressure. The SEC is also presented in terms of a dimensionless parameter, namely, the specific energy indicator (SEI), which can be used as a membrane property to indicate the SEC of the membrane element for a given process recovery rate and feed osmotic pressure. The SEC calculations are presented for desalting a NaCl solution with a salinity of 35,000 mg/L over a wide range of recovery rates and membrane element permeate flow rates. The calculations showed that for a membrane element with a permeate flow rate of 2 m 3 /h operating at 50% system recovery rate, the SEC of the RO process can be reduced by more than 35% if the membrane element flow rate factor is doubled, for example, from a value of 20 to 40 L/h.bar.

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A two-step forward osmosis (FO) desalination process combining both FO and reverse osmosis (RO) systems has been developed by the Centre for Osmosis Research and Applications at the University of Surrey and commercialised by Modern Water plc. In the FO + RO process seawater was used as feed water (FW) and a concentrated aqueous solution was used as a draw solution (DS). By taking advantage of natural osmosis, pure water is transferred from the FW to the DS and then recovered from the DS by the RO process utilising low resistance membranes, and hence lower specific energy consumption (SEC). This paper presents results of FO experiments conducted on flat sheet membrane using a bench-scale rig. The osmotic agent investigated in this study was magnesium sulphate, which is non-toxic, and highly soluble in water. Furthermore experiments were carried out on the RO pilot in order to regenerate the DS for reuse in the FO process and produce clean water. This paper also presents some pilot plant results and data from commercial plants in Oman and Gibraltar. The data demonstrates the efficiency of the FO + RO compared with the conventional RO process in terms of SEC and membrane fouling performance.

© 2015 Balaban Desalination Publications. All rights reserved. This work investigates the effectiveness of sodium chloride and sucrose binary draw solutions in a forward osmosis pilot plant unit with either deionised or salt water feeds. Specifically, the effects of draw solution concentration on water flux through the membrane, the overall water recovery and the specific energy consumption of the unit are considered. For both feed types, sodium chloride draw solution exhibited a relatively high effectiveness in terms of all the measured performance indicators. Further, improvements in flux and recovery were also achievable with an increase in the sodium chloride (draw solution) concentration. In contrast, a sucrose-based draw solution led to a severe deterioration of the membrane performance that could not be effectively overcome by an increase in the draw solution concentration. This observation was attributed to the relatively large increase in the viscosity of the draw solution with increase in sucrose concentration. Interestingly, in the case of a salt water feed, an increase in the sucrose draw solution concentration led to a relatively small increase in flux and recovery, suggesting some complex but favourable interaction between the salt and sucrose due to the reverse diffusion of the salt into the draw solution

This paper presents a study on the potential of osmotic energy for power production. The study includes both pilot plant testing and theoretical modelling including cost estimation. A projected cost of 30 $/MWh of clean electricity could be achieved by using a Hydro-Osmotic Power (HOP) plant if a suitable membrane is used and the osmotic potential difference between the two solutions is greater than 25 bar; a condition that can be achieved in a number of ways. Results have shown that the membrane system account for 50%-80% of the HOP plant cost depending on the osmotic pressure difference level. Thus, further development in membrane technology and identifying suitable membranes would have significant impact on the feasibility of the process and the route to market. The results have shown the strong dependency of the produeced power cost on the membrane permeability. The results have also shown that a substantial reduction in the membrane area requirment for a given power output can be acheived as the osmotic pressure differnece between the two solutions increases beyoned 50 bar.

The present work includes studying the kinetics of the adsorption of two sugars (maltose and glucose) on activated carbon (GAC) and comparison between them. These sugars are used as draw solution in the forward osmosis process in MOD-SET system (manipulated osmosis desalination system, MOD combined with solute exchange technique, SET). In this work, batch experiment in a stirred tank was carried out to study kinetics adsorption. The experiment was carried out using HPLC to determine the concentrations of sucrose and maltose before and after adsorption. The kinetic models used are pseudo-first order, pseudo-second order, intraparticle diffusion and mass transfer model. The findings indicates that sucrose and maltose sorption onto GAC are both well represented by the pseudo second order model.