For brackish water desalination, there is necessity to reduce the volume of saline waste water generated in existing processes due to scarcity of water and to cope up with increasing water demand. The electrodialysis process typically known for its higher water recovery rate with competitive energy consumption per unit volume of clean water produced. Theoretical and experimental investigation of electrodialysis in the feed water composition of Indian ground water would make this technology more adaptable at commercial level. With the capability of bipolar membrane to split water into hydroxide ions and protons, the electrodialysis with bipolar membrane process can produce acid and base solution from the corresponding salt solution. This onsite acid and base production capacity of electrodialysis with bipolar membrane process reduces the need of purchasing these chemicals and also reduces the saline wastewater generation in many industries including dairy industry. This research is aimed to study the electrodialysis system at pilot plant scale installation along with long term testing would make this technology one step ahead in desalination and wastewater treatment.

The design and operation of FO systems require accurate prediction of performance according to the operating parameters. Performance parameters such as water flux, reverse solute flux (RSF), specific reverse solute flux (SRSF), recovery and rejection are influenced by operating parameters including temperature, concentration difference (CD), and flow rates of feed solution (FS) and draw solution (DS). Whereas previous studies analysed the effect of only one or two operating parameters on one or two output parameters, this study provides a complete investigation into the effects of all operating parameters on all output parameters important for performance. A bench-scale FO setup using an advanced FO membrane and NaCl draw solution has been studied and compared to a predictive model, giving agreement within 10 %. Water flux and RSF increased with temperature, CD and flow rate. SRSF decreased with temperature, increased with CD, and increased as flow rates of FS and DS increased. Increasing temperature or CD increased the recovery; whereas increasing the flow rate of FS or DS reduced the recovery. Rejection dropped at higher CD and flow rates. Hence, it is recommended to operate at lower CD and flow rates to achieve higher recovery and rejection.

Concept of integrated brackish water batch reverse osmosis – forward osmosis (BRO – FO) is relatively new in the field of desalination. Recovery of the reverse osmosis (RO) system can be elevated using the free piston BRO concept, and the specific energy consumption (SEC) can be reduced. This study focuses on exergy, advanced exergy, and parametric analysis of the integrated BRO - FO system. The conventional exergy analysis suggests that the largest rate of exergy destruction is associated with the system's RO membrane module and pump, with values of 6.51 and 87.06 %, respectively. However, advanced exergy analysis shows that this rate can be reduced by 3.53 % and 62.89 %, respectively. Endogenous exergy destruction of pumps and membranes is higher compared to exogenous exergy destruction. These results are utilised to determine the system's optimal performance using parametric analysis. Sensitivity analysis was utilised to obtain an optimum recovery for system design, fresh water cost (FWC), and specific solution cost (SSC). The BRO can achieve >80 % recovery with 0.43 kWh/m3 SEC, and FO technology helps to attain minimal/zero waste discharge. Thus, a FWC of 0.50 $/m3 and a SWC of 0.44 $/m3 can be achieved.

Forward osmosis is a promising membrane-based desalination technique that uses less energy compared to other technologies. Hybridization of forward osmosis in the company of different technologies makes it an attractive technology. However, the availability of commercial membranes, the cost of the membrane, low water flux, low retention of impurities, and availability of the draw solution are the major obstacle to the commercialization of forward osmosis technology. Application and mass transfer are the major covered area of forward osmosis technology. In this study, mathematical modeling and simulation are carried out for the flat sheet membrane/Plate and frame membrane, which comprise mass balance, permeate flux, and effect of concentration polarization. Membrane orientation, draw and feed solution flow rate, the concentration of draw solution and feed solution, and the flow arrangement of the solutions are variable inputs to the mathematical modeling. The result shows that higher dilution of the draw solution can be achieved using a lower draw solution flow rate and a higher feed solution flow rate. Also, the parallel flow and counter flow arrangement in forward osmosis is slightly influence the variation in the concentration difference for both streams. Wisely choosed operating conditions using mathematical modeling give better membrane performance.

Hybridization of electrodialysis (ED) and batch reverse osmosis (BRO) process is used to reduce the brine volume and water production cost. The ED process has the benefit of high water volume recovery in brackish water desalination, while reverse osmosis can produce pure water at a low production cost. Here, a simple hybrid process layout is preferred in which the ED process is kept in the reject stream of the BRO process and permeate from both ED and BRO is mixed. Recovery of the ED process is kept at 70% which can decide the blending ratio of ED and BRO permeates. The capital cost and operating cost of ED and BRO processes are used to calculate water production cost. The water production cost from the hybrid ED–BRO process is found to be 0.22 $ m−3 of freshwater when the feed concentration is 1,100 ppm. The cost increases from 0.20 to 0.34 $ m−3 with feed concentration from 1,000 to 2,000 ppm. In the cost, a major portion comes from the capital equipment in which the highest contributor is the membrane for both ED and BRO processes.. 

Forward osmosis technology is a highly potential and energy-efficient technology to treat different types of wastewater, but commercialization of this technology seems far ahead. Economic evaluation and technological alignment are crucial assessments for commercializing these technologies. Domestic wastewater is used as a feed solution, while reverse osmosis reject/brine is used as a draw solution in the forward osmosis system. Capital expenditure and operating expenditure were used to calculate specific solution costs. Assuming membrane costs 30 $/m2, specific solution cost is obtained 0.37 $/m3. The current study examines the effect of water flux, feed solution flow rate, and draw solution on specific solution cost. Analysis suggests that the high membrane flux of forward osmosis system is the reason for lower specific solution cost. Despite good innovation potential, FO needs to overcome technical issues like less water flux, availability of the draw solution, poor retention of the impurities, advances in membrane rejections, fouling potentials, and membrane cleaning processes. The techno-economic assessment suggests a technological aspect that needs to improve to commercialize the technology.

Recently, forward osmosis (FO) has attracted attention in many potential applications including food processing, fertilizers and manufacturing industries. This study investigates the effects of feed solution (FS) and draw solution (DS) temperature on the water flux, reverse salt flux, and specific reverse salt flux. The temperature of both the DS and FS were varied at the same time. Four typical temperatures such as 20 °C, 25 °C, 30 °C and 35 °C were selected to maintain at FS and DS sides, respectively, for each iteration. Except for the temperature, the other operating conditions like concentration, flow rates, and the type of membrane used were not varied in this experiment. The experiments were performed with tap water as FS and 1.5 M of NaCl as DS. The flow rates of the DS and FS were maintained at 15 L min−1 and 25 L min−1, respectively. The membrane used was the hollow fiber forward osmosis (HFFO.6) membrane procured from Aquaporin A/S, Denmark. The results showed that as temperature increased from 20 °C to 35 °C, the water flux, reserve salt flux (RSF), and specific reverse salt flux were enhanced. This was due to the enhanced diffusion coefficient of both DS and FS on increasing the temperature. This further reduces the concentration polarization and in turn augments the water flux. However, consequently, reverse and specific reverse solute flux also increased on temperature, which is not desirable for an efficient FO system. Hence, it is recommended to operate the FO at a minimum required temperature considering the other influencing other operational parameters such as specific reverse solute flux, recovery and rejection percentage.

Efforts to improve the performance of RO desalination include new membranes and new system configurations. Batch RO is an innovative configuration which helps to minimize Specific Energy Consumption (SEC) at high recovery. However, there is a lack of experimental studies regarding the performance of different membranes in batch RO. In this study, we tested four 8-in. RO membranes of different permeabilities in a free-piston batch RO system to assess how membrane properties affect performance. Tests were conducted with brackish feed water containing 1000–5000 mg/L of NaCl, at recovery of 0.8. Performance in terms of SEC, permeate quality and salt rejection was quantified. SEC and salt rejection varied considerably from low-permeability to high-permeability membranes. For the lowest permeability membrane rejection was >95 %, whereas for the higher permeability membranes it was only 82–96 %. SEC with high-permeability membranes was approximately 25–29 % lower than with the lowest permeability membrane. Using a verified model, we predict that on increasing the permeability from 5 to 20 L/m2/h/bar, hydraulic SEC would go down further by 17–28 % using ultra high-permeability membranes. Though this study shows the potential for SEC reduction, it also underlines the limitations of current commercial membranes and therefore the need for membranes with even higher permeability.

Energy, exergy, economic and environmental analysis is applied to a novel FO system. The system is designed to achieve minimal/zero liquid discharge with low specific energy consumption. Up to 43 % recovery is obtained with desired output in terms of salinity of diluted draw solution and concentrated feed solution. The specific energy required to produce diluted draw and concentrated feed solutions for the proposed application is as low as 0.0285 kWh/m3. In this study, DS-Lumen/AL-DS mode shows specific energy savings of 49.5 % in performed cases compared to FS-Lumen/AL-FS mode using a less flow rate of draw solution. The process design is done to reach the appropriate salinity level at the system outlet. The feed solution connection is in the series between membranes, which helps to dilute the draw solution, while the draw solution connection is in parallel between membranes to achieve desired salinity level at the outlet. The influence of the feed and draw solution temperature and flow rate on the membrane performance is observed. Capital and operating costs of the membrane and other costs, such as tank and chemical solution costs, are significant contributors to the total cost. The specific solution (total output of FO system) cost is estimated at 0.23 $/m3. Environmental analysis suggests that the deployment of solar energy as an energy source of the system reduces 93.06 % of CO2 emissions compared to fossil fuel (coal).

Groundwater salinization is a problem affecting access to water in many world regions. Though desalination by conventional reverse osmosis (RO) can upgrade groundwater quality for drinking, its disadvantages include unmanaged brine discharge and accelerated groundwater depletion. Here, we propose a new approach combining RO, forward osmosis (FO), and halophyte cultivation, in which FO optimally adjusts the concentration of the RO reject brine for irrigation of Salicornia or Sarcocornia. The FO also re-uses wastewater, thus, reducing groundwater extraction and the wastewater effluent volume. To suit different groundwater salinities in the range 1–8 g/L, three practical designs are proposed and analyzed. Results include specific groundwater consumption (SGC), specific energy consumption (SEC), wastewater volume reduction, peak RO pressure, permeate water quality, efficiency of water resource utilization, and halophyte yield. Compared to conventional brackish water RO, the results show superior performance in almost all aspects. For example, SGC is reduced from 1.25 to 0.9 m3 per m3 of drinking water output and SEC is reduced from 0.79 to 0.70 kW h/m3 by a FO–RO–FO system treating groundwater of salinity 8 g/L. This system can produce 1.1 m3 of high-quality drinking water and up to 4.9 kg of edible halophyte per m3 of groundwater withdrawn. 

Bipolar membrane electrodialysis (BMED) for acid and base recovery and batch reverse osmosis (BRO) for water recovery are analyzed technically and economically as a dairy wastewater treatment solution. The proposed process layouts also aimed to utilize recovered water and chemical within same industrial plant. The hybridization of BMED with BRO process is used to reduce capital and operating cost of BMED unit and compared with the standalone BMED process. The analysis reveals that the hybridization of BRO-BMED system achieve 25.8% less unit cost and three times higher concentration of acid and base chemicals compare to standalone system. The comparison of system is done at optimum current density of BMED process and permeate flux of BRO process. Sensitivity analysis of permeate flux, current density and feed salinity is carried out. The higher feed concentration is desirable and reduces the cost in BMED process and same with current density but up to 409 and 255 A/m2 in hybrid and standalone system respectively. In hybrid system, the multi-response surface analysis observes that higher permeate flux in BRO reduces the BMED cost but increases the BRO cost and the minimum cost of 14 USD/kmol is achieved at 26 LMH permeate flux.

Hybrid semi-batch/batch reverse osmosis (HSBRO) is a new method of high-recovery desalination that provides low Specific Energy Consumption (SEC) in a compact design. In this first experimental study on HSBRO, we report SEC over a range of operating parameters using brackish feed water. For example, at 500–1500 mg/L feed concentration, and recovery of 0.94, we measured hydraulic and electrical SEC of 0.20–0.31 kWh/m3 and 0.42–0.54 kWh/m3 respectively, using a flux of 18.9 L/m2/h and obtaining an output of 17.5 m3/day. Second law efficiency was 7.8–17.8 % thus improving on available multistage and semi-batch RO systems. A model of the system, that includes the effect of finite salt rejection, predicts SEC with accuracy of 1–3 %. With improvements in membrane permeability, valves, and pump efficiency, we predict electrical SEC lowered to 0.14–0.28 kWh/m3 and second law efficiency elevated to 22.8–34.5 %. Though simple batch RO can achieve comparable SEC to HSBRO, for recovery as high as 0.94 it would require an impractically large work exchanger. The model shows that feed of salinity up to 6000 mg/L may be treated with recovery of 0.95 and peak system pressure < 120 bar, indicating great potential in ZLD and MLD applications.

Salinity negatively influences crop growth, but several salt-tolerant plant species (halophytes) are viable crops. Sarcocornia fruticosa (ecotypes EL and VM) is currently cultivated, but there is demand for new crop candidates and higher biomass production. Salicornia brachiata Roxb. and Arthrocneum macrostachyum L. are considered novel crops, and to realize their potential, their response to salinity and nitrogen nutrition was compared to S. fruticosa ecotypes. Experiments revealed that higher N supplemented with lower NaCl significantly increased fresh and dry shoot biomass. Lower biomass was obtained at lower nitrogen supplemented with elevated NaCl, whereas total soluble solids content positively correlated with NaCl fertigation in both Sarcocornia ecotypes. Protein content increased with a lower nitrogen supply. Anthocyanins and oxygen radical absorbance capacity were highest in S. fruticosa EL and A. macrostachyum at higher NaCl supply. The results show that halophytes have a variety of strategies to cope with high NaCl, even between ecotypes of the same species. Notably, repetitive harvesting of S. brachiata delayed flowering enabling year-round biomass production. Additionally, S. brachiata accumulated higher biomass than Sarcocornia VM when grown in a greenhouse at higher radiation than in a growth room and strongly supports its inclusion as a cash-crop halophyte.

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

Batch reverse osmosis (RO) is  a  promising approach to  high-recovery desalination. It  has  low  energy consumption, but system size increases sharply with recovery because of the need for a large work exchange vessel. In this study, we propose a compact hybrid batch/semi-batch reverse osmosis (HBSRO) system incorporating aspects of each approach. HBSRO works in three phases, i.e. semi-batch pressurisation phase, batch pressurisation phase, and finally purge-and-refill phase. We analyse ideal and practical cases of HBSRO to gain understanding about the specific energy consumption (SEC) and size of the system. In the ideal analysis, HBSRO can halve the size of work exchange vessel while incurring just a 5% energy penalty compared to batch RO at all recoveries. In the practical case, accounting for nonidealities, HBSRO has lower SEC than batch RO at recovery over 0.9, because a smaller volume of work exchange vessel minimises the energy penalty of the purge-and-refill phase in HBSRO. The reduced volume not only makes HBSRO more practical, but also improves energy-efficiency through reduced losses. Thus, our  study highlights that  HBSRO is  highly flexible, achieving high recovery, compact size, and low SEC – advantages that are  especially important in  minimal or  zero liquid discharge applications. 

Batch RO is a concept for achieving the minimum possible energy consumption in desalination, even at high recoveries. We present a batch RO design that operates cyclically in two alternating phases. The system uses a free piston, housed in a pressure vessel, to transfer pressure from the feed fluid to the recirculating fluid. No complete design procedure for this configuration currently exists. To fill this gap, we present a systematic model based on justified assumptions. The specific energy consumption (SEC) is broken down into contributions from the feed pump, recirculating pump, and auxiliary loads. The calculation of feed pump SEC includes three non-ideal correction factors: concentration polarisation, longitudinal concentration gradient, and salt retention. The model requires only the solution of explicit algebraic equations, without need of specialised numerical techniques, and is implemented in a simple 3-step procedure. The model is applied to an example involving desalination of brackish water using an 8-inch spiral-wound RO module. The design parameters are explored and optimised in a sensitivity analysis. The results show that the optimised batch RO at 80% recovery can produce fresh water with low-energy consumption, achieving 2nd law efficiency of 33.2% compared to 10–15% for conventional brackish water RO.

Effect of flow velocity and cell-pair thickness in electrodialysis (ED) is studied. The production cost includes pump energy, while the size of the system is considered as an output variable. The performance of ED system depends on three categories of process parameters namely water quality data, stack configuration and flow characteristic inside the stack. The design of ED system is complex due to interrelation among the system variables so the design calculation chronology steps are developed with flow-chart for the fix feed salinity of groundwater and salt removal rate. The effect of recovery ratio on capital and energy cost is studied and found unidirectional. Sparingly soluble salt present in feed decides the upper limit and obtained 70–75% recovery rate based on the feedwater quality. The optimum value of the linear flow velocity and cell-pair thickness can be obtained by the trade-off among capital cost, stack energy cost and pumping energy cost. Simultaneous effect of both the variable on minimizing the total cost gives the narrow working range of flow velocity 15–17 cm/s and 0.4–0.8 mm thickness. The minimum production cost of 0.08 USD/m3 is obtained at 16 cm/s velocity and 0.5 mm thickness.