Research On Forward Osmosis Desalination Efficiency And Effect Factors

Using membrane separation technology for desalination of sea water from seawater to freshwater resources is one important way. Traditional reverse osmosis membranes can effectively achieve the separation of the solute and solvent (water), but there is a high energy consumption and serious membrane fouling. Recently, the forward penetration (Forward Osmosis, FO) as a new type of membrane technology is causing widespread concern. FO to take advantage of the osmotic pressure of the solution itself (rather than the external pressure) drive the water molecules and the separation of the solute material, with low energy consumption, high efficiency, small membrane fouling advantage, it is possible to make desalination easier, economical and practical and therefore has potential applications in the desalination field. However, the forward penetration technology applied to desalination research is still at the exploratory stage, yet to see a related studies reported in the country. Especially FO membrane asymmetrical structure causes a serious concentration polarization and temperature polarization resulting from both sides of the solution at different temperatures, these factors largely restricted FO engineering applications.First, the paper examines that the FO in the field of water treatment may be of potential applications and feasibility. Results show that, FO has the higher the retention rate (99.8%above) for treating heavy metal ions(Zn2+, Cu2+, Cr3+, Ni2+Cd2+). And iron manganese water also have better treatment effect. In addition, using FO to treat sea water(Mg2+、Na+、K+、Ca2+、Cl-、SO42-) also get a higher retention effect (98.6%above). But after20min, water flux will has a large attenuation, since then the water flux stabilized. Therefore, in order to alleviate the concentration and the temperature difference between polarization caused due to the use of asymmetric membrane in the FO, FO over water flux, subject to the FO process principle and the asymmetric membrane structure caused by the polarization as a starting point to study the FO process, concentration polarization, the generation and variation of temperature difference between polarization, put forward an effective strategy to control concentration polarization, and the the FO heat flux in non-isothermal conditions and influencing factors, FO amplification test provide a basis for practical and engineering applications.The FO water flux in different membrane toward are different. The results show that the active layer (Active layer) toward the liquid (Feed solution, AL-FS) mode, the internal concentration polarization effect of water flux(Draw solution, AL-DS) mode, the support layer is very poor, so the water flux under the same experimental conditions (The concentrations of FS and DS, the flow rates), AL-DS mode greater than the water flux in the AL-FS mode. For internal concentration polarization control, the diffusion coefficient of water molecules in the support layer is a key factor to control the internal concentration polarization; external concentration polarization, increasing the cross-section flow able to compress the fluid boundary layer of the membrane surface, therefore can effectively reduce the impact of the external concentration polarization.Finally, the FO water flux under different temperature conditions were compared, the results show that the FS and DS both sides of the temperature difference exists, due to temperature changes caused by changes of viscosity and diffusion coefficient of water molecules of the FS side affect water through a key factor in the amount of, mainly because of the increase in temperature can reduce the viscosity of the water molecules within the diffusion layer (decreases39.32%), to improve its diffusion rate (increased by58.87%). In contrast, the DS side of the solution osmotic pressure due to temperature changes caused by changes in transmembrane water flux in FO is not significant (the osmotic pressure of the DS is only6.83%). The study also found that inevitably occur when the membrane on both sides of the temperature difference heat transfer, increasing the flow rate causes the membrane surface turbulence intensified, the temperature difference between the polarization boundary layer is compressed, so the boundary layer heat transfer coefficient hFS-BL, or hpS-BL value increases, the membrane on both sides to speed up heat transfer; the temperature of the membrane surface compared to the low flow rate, the closer the temperature of the bulk solution.