A compact hybrid batch/semi-batch reverse osmosis (HBSRO) system for high-recovery, low-energy desalination

Novel Tri Hybrid Desalination Plants

This work focuses on Specific Energy Consumption (SEC) in batch and semi-batch reverse osmosis (RO) processes. It is proved from optimal control theory that the minimal SEC in semi-batch RO occurs at constant flux conditions, similar to conclusions in both batch RO and continuous, infinite-stage RO. While semi-batch RO is comparable to two- or three-stage RO at the thermodynamic limit (i.e. zero flux), its performance may be severely compromised by finite flux applied in desalination and efficacy of flushing before the next filtration step. Batch RO is even more susceptible to salt retained during flushing. On the basis of typical flux used in industrial desalination and a 95% flushing efficacy, semi-batch RO at the cyclic steady state is only similar to one-stage RO at low recoveries (e.g. 30 and 40%) and excels slightly at high recoveries (e.g. 50 and 60%). Batch RO may outperform one-stage RO but is still not as good as two-stage RO. Reducing salt retention and operating at a reduced flux are ways to make batch and semi-batch ROs energy advantageous over their continuous counterparts.

A new approach for freshwater production and energy recovery from an oil field

Desalination is a method for producing water for human consumption, irrigation or industrial utilisation. In this study, a reverse osmosis (RO) system for brackish water desalination was theoretically investigated to produce both potable drinking and agricultural water with a lower overall and specific energy consumption. As a case study, the Main Outfall Drain in Iraq is used as the brackish water source. A numerical model based on solution-diffusion theory was developed in Matlab Simulink and used to analyse the design and performance of an RO system. The effect of feed water temperature, pressure, salinity and recovery ratio on the efficiency of the whole RO system was investigated for a wide range of design considerations. The design of an RO system for this application was optimised and economic assessment carried out. Results show that with boosting recovery ratio from 30% to 60%, the specific energy of desalinated water production below 400ppm was reduced from 2.8kWh/m3 to a more economically favourable value of 0.8kWh/m3, when utilizing a pressure exchanger as a recovery device. Salt rejection was reduced from 97% to 88% to obtain large quantities of water for irrigation with an acceptable salinity (<1600ppm), for agricultural use. The reduction in salt rejection is influenced by the feed water temperature and pressure; also the average pore diameter of the RO membrane and in turn determines the reduction in system energy consumption. It was found that the total cost to produce 24,000m3/d of water from a feed salinity of 15,000ppm and a water quality of <400ppm would be 0.11£/m3 with a corresponding investment cost of £14.4million for the drinking water, and for irrigation) obtained product <1600ppm) are £0.9/m3 and £11.3million.

Batch reverse osmosis (BRO)-adsorption desalination (AD) hybrid system for multipurpose desalination and minimal liquid discharge

Batch RO is designed to achieve high energy efficiency and high recovery in desalination. However, so far relatively few experiments on batch RO have been reported. Here we present an extensive experimental study of a single-acting, free-piston batch RO system using an 8-inch spiral wound membrane. The system was tested in the laboratory with brackish feed water containing up to 5 g/L NaCl. The objective was to quantify system performance in terms of Specific Energy Consumption (SEC), recovery, rejection, and output. Sensitivity to permeate flux and recirculation flow rate was also investigated. Performance was compared against the predictions of a theoretical model that accounts for salt retention, concentration polarization, and longitudinal concentration gradient in the RO module. For the first time, osmotic backflow was measured and incorporated into the model. For feed concentrations ranging from 1 to 5 g/L and recovery of 0.8, hydraulic SEC was measured in the range 0.22–0.48 kWh/m3 and electrical SEC in the range 0.48–0.83 kWh/m3. With improvements to the membrane permeability from 4.4 to 8 LMH/bar, selection of more efficient pumps, and reduction of valve friction losses, the model predicts that hydraulic SEC will be lowered to 0.14–0.39 kWh/m3.

Design, modelling and optimisation of a batch reverse osmosis (RO) desalination system using a free piston for brackish water treatment

Membrane compaction in batch reverse osmosis operation and its impact on specific energy consumption

A systematic approach towards optimization of brackish groundwater treatment using nanofiltration (NF) and reverse osmosis (RO) hybrid membrane filtration system

Inorganic fouling mitigation by salinity cycling in batch reverse osmosis

Renewable energy powered membrane technology: Impact of solar irradiance fluctuations on performance of a brackish water reverse osmosis system

Energy efficiency of batch and semi-batch (CCRO) reverse osmosis desalination

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.

Multiple Reverse Osmosis sub-units supplied by unsteady power sources for seawater desalination

Experimental comparison of the performance of two reverse osmosis desalination units equipped with different energy recovery devices