The forward osmosis desalination process usually includes osmotic dilution of draw solution and freshwater production from diluted draw solution. There are two types of forward osmosis desalination based on the different water production methods. One applies heat sinking draw solution that broke down into volatile gases , these gases could also be recycled during the thermal decomposition and generate high osmotic pressure. The other is used as filtration or dilution of water. For instance, the combination of reverse osmosis and forward osmosis could be used for drinking water treatment or brine removal, forward osmosis could also be a fully or partly replacement of ultrafiltration under certain circumstances. Recent studies in materials science also proved that forward osmosis could be used to control drug release in the human body, it could also control the food concertation in the production phase. Regarding the semi-permeable membrane used in Forward osmosis, the tubular membrane is more functional for many reasons. The tubular membrane is one of the membranes that allow solution flows bidirectionally of the membrane, it maintains high hydraulic pressure without deformation due to the self-supported feature, it is also easier to fabricate while retaining high flexibility and density. Although there is a substantial amount of energy required to treat seawater using Forward Osmosis technology, its potential has been demonstrated through bench-scale experiments,fodder system indicating further investigations are needed to evaluate its commercial application. Seawater desalination has provided freshwater for over 6% of the world’s population. One of the commonplace models of forward osmosis seawater treatment is using a hollow fiber membrane. The key parameter in the hollow fiber membrane model is the minimum draw solution flow rate.

When the flow rate increases, the energy requirement increases as well. In an ideal Forward Osmosis process, CDO and CFI should be equal. Figure 2-3 below shows the schematic diagram of the forward osmosis membrane module. To assess the energy consumption in the FO process, the solution concentrations and flow direction of the module should be determined first. The data supports that the energy required for pumping the draw solution is less than that for pumping feed solution. To determine the effects of the direction of hydraulic pressure in the module, different modules with various concentration solutions and flow rates are designed to compare the energy efficiency. In conclusion, the results demonstrate that to reduce the energy consumption of seawater desalination, the FO module need to optimize these diameters. Also, the flow rates and concentrations of draw and feed solutions play a major role in terms of energy efficiency. The module illustrates that when a high flow rate feed solution is on the shell side and a draw solution with a low flow rate is on the lumen side, the system consumes less energy consumption. Another vital implementation of Forward Osmosis is food concentration/enrichment. Multiple studies concluded that FO is efficient when it comes to dewatering for food production.  Compared to the traditional concentration method, such as pressure driven membrane, FO requires less energy and yields less nutrition loss. Nutrition loss refers to the reduction of monomers fructose here. A closed-loop feed solution and draw solution system are built as figure 2-4 below. Garcia-Castello tested two membranes in the system above. A flat sheet of cellulosic membrane and an AG reverse osmosis membrane. AG membrane refers to a certain designation of membrane manufactured by Sterlitech. The result shows that the AG membrane has a higher salt rejection rate. During the procedure, once the water flux reaches a constant value, a feed stock solution is added to the tank to reach the next feed solution concentration.

At the end of the experiment, the highest feed solution is 1.65M sucrose. By comparing performances of different membranes, the AG membranes yield better results when concentrating on sucrose solution due to its tucker support structure. The temperature also has a significant impact on water flux. Usually, higher temperature yields higher water fluxes. Compared to the concentration factor of RO, FO has a better concentration factor of 5 while it requires much less energy.Fertilizer drawn forward osmosis applies the forward osmotic dilution of the fertilizer draw solutions. This technology could be used for direct agricultural irrigation. Fortunately, most of the fertilizers could be used as a draw solution for FDFO. Fertilizer drawn forward osmosis shares the same principle with forward osmosis. Freshwater as feed solution flows through the semi-permeable membrane to the fertilizer draw solution under the natural osmotic pressure. Additional treatments might be required to reach the water quality for different purposes. Regarding the nitrogen removal purpose for this review, operating conditions such as feed solution concentration, feed solution water flow rate, and specific water flux can affect the effectiveness of nitrogen removal. Fertilizer-drawn forward osmosis has common applications in water recycling and fertigation applications. Nanofiltration is a viable solution for diluting the fertilizer draw solution for recycling purposes. Fertilizer-draw forward osmosis technology has used brackish water, brackish groundwater, treated coal mine water, and brine water as the feed solutions. In another word, water that has a relatively lower total dissolved solid could be feed solution for fertilizer drawn forward osmosis. Moreover, fertilizer drawn forward osmosis is also effective on biogas energy production when it is applied to an anaerobic membrane bioreactor as a hybrid process. In conclusion, fertilizer drawn forward osmosis is effective for sustainable agriculture and water reuse. Its considerable recovery rate could be used as the hydroponics part in an anaerobic membrane bioreactor . Due to the scarcity of fresh water in arid areas, hydroponics has been used for vegetable production. In the field of hydroponics, a subset of hydroculture, crops are cultivated in a soilless environment, their roots are exposed to mineral nutrient solutions or fertilizers. Without soil culture, this type of agricultural production precludes certain aspects that are associated with traditional crops production, including soil pollution, lower fertilizer utilization efficiency, or spread of pathogens. This technology also allows the production of crops in arid, infertile, or simply too populated areas. However, economic cost aside, this technique requires both a large amount of fresh water and fertilizers compared with soil-based crops production. This could easily cause detrimental effects to the environment such as water waste and contamination, excessive nitrogen, potassium, and phosphate resulting in eutrophication. To achieve the balance between cost, efficiency, and quality, reverse osmosis and ultrafiltration are more advanced and general approaches compared to biological seawater treatments. In terms of treating seawater, the hydroponic nutrient solutions demonstrate similar performance compared with other aqueous solutions of a lower molecular weight salt. By utilizing certain membrane technologies, treated effluent has reduced the presence of pathogens and remained the ability to be better integrated into the fertigation system for direct application. The potential of the fertilizer drawn forward osmosis process was investigated for brine removal treatment and water reuse through energy-free osmotic dilution of the fertilizer for hydroponics. Nanofiltration is a pressure-driven membrane process, it refers to a special membrane process that removes dissolved solutes. The membrane is with pores ranging from 1 to 10 nanometers, hence the name “nanofiltration”. Nanofiltration uses a similar principle as reverse osmosis, it is a water purification process that requires pressure,fodder system for sale and its membranes are permeable to ions. Nanofiltration is practical in removing organic substances from coagulated surface water, it is also economic and environmentally sustainable. In terms of size and mass of solvents removed by nanofiltration membranes, they usually operate in the range between reverse osmosis and ultrafiltration: removing organic molecules with molecular weights from 200 to 400. Nanofiltration membranes can also effectively remove other pollutants including endotoxin/pyrogen, pesticides, antibiotics, soluble salts, etc.

Depending on the type of salt, it has various removal rates. For salts containing divalent anions, such as magnesium sulfate, the removal rate is around 90% to 98%. However, regarding salts containing monovalent anions, such as sodium chloride or calcium chloride, the removal rate is lower, which is between 20% to 80%. The osmotic pressure across the membrane is typically 50-225 psi. One of the advantages of Nanofiltration is that it uses lower pressure and sustains higher water flux. Plus, it has highly selective rejection properties. Typical applications for nanofiltration membrane systems include the removal of color , total organic carbon from surface water, reduction of total dissolved solids , and the removal of hardness or radium for well water. In 1952, Congress passed the Saline Water Conversion Act, which is aimed at resolving the shortage of freshwater and excessive use of underground water. Two years after the act, the first desalination plant in the United States was built in 1954 at Freeport, Texas. The planet is still operative to date and is undergoing improvement. U.S. Department of Agriculture predicts to supply 10 million gallons of fresh water per day in 2040. The Claude “Bud” Lewis Carlsbad Desalination is the largest desalination plant in the U.S. The plant delivers almost 50 million gallons of fresh water to San Diego County daily. Due to objective conditions, desalination has prevailing existence in regions such as the Middle East, where the largest desalination plant worldwide stands in terms of freshwater production. With 17 reverse osmosis units and 8 multi-stage flashing units, the plant can produce more than 1,400,000 cubic meters of fresh water per day. In 1960, there were only 5 desalination plants in the world. By the mid-1970s, as the conditions of many rivers deteriorated, around 70% of the world’s population could not be guaranteed sanitary and safe freshwater. As a result, water desalination has become a strategic choice commonly adopted by many countries in the world to resolve the shortage of fresh water, its effectiveness and reliability have been widely recognized. The limitation and uneven distribution of freshwater resources have been one of the most prevailing and serious problems faced by people living in arid areas. To reduce its severity, saline water or wastewater desalination has always been a constantly researched and applied solution. In many arid regions, the desalination of seawater is evaluated as a promising solution. Despite that seawater holds around 96.5% of global water resources , the global-scale application of seawater desalination is hindered by the cost, both financially and energy-wise. With the development of energy-saving technologies for seawater desalination, it is viable to use saline, such as seawater and brackish water to produce freshwater for industries and communities. Commonly used methods require water pumping and a considerable amount of energy. As a result, forward osmosis is receiving increasing interest in this field since the FO process requires much less energy. One of the research teams at Monash University in Australia has demonstrated a solar-assisted FO system for saline water desalination using a novel draw agent. The research team led by Huanting Wang and George P. Simon has investigated the potential of a thermoresponsive bilayer hydrogel-driven FO process utilizing solar energy to produce fresh water by treating saline water. This Forward osmosis process is equipped with a new draw agent: a thermo responsive hydrogels bilayer. Compared to one of the most used draw agents , this duallayered hydrogel is made of sodium acrylate and N-isopropyl acrylamide , which induces osmotic pressure differences without the need for regeneration. The thermo responsive hydrogels layers generate high swelling pressure when absorbing water from high-concentrated saline. During testing, researchers used a solution of 2,000 ppm of sodium chloride, which is the standard NaCl concentration for brackish water. Water passes through the semipermeable membrane and is drawn from saline solution to the absorptive layer . The hydrogel can absorb water up to 20 times larger than its regular volume. Next, the thermo responsive hydrogel composed only of NIPAM then absorbs water from the first layer. When the dewater layer is heated to 32 °C, which is the lower critical solution temperature , the gel collapses and squeezed out the absorbed fresh water. Draw agents like ammonium bicarbonate are required to be heated up to 60 °C, then distilled at a lower temperature for regeneration. By focusing the sunlight with a Fresnel lens, the concentrated solar energy can help dewatering flux reach 25 LMH after 10 minutes, which is similar to the water flux of ammonium bicarbonate.