Osmotic power is to produce electric power by using the chemical potential of two flows with the difference of salinity. Water permeates through a semipermeable membrane from a low concentration feed solution to a high concentration draw solution due to osmotic pressure. In a pressure retarded osmosis (PRO) process, river water and wastewater are commonly used as low salinity feed solution, whereas seawater and brine from the SWRO plant are employed as draw solution. During the PRO process using wastewater effluent as feed solution, PRO membrane fouling is usually caused by the convective or diffusive transport of PRO which is the most critical step of PRO membrane in order to prevent membrane fouling. The main objective of this study is to assess the PRO membrane fouling reduction by pretreatment to remove organic matter using coagulation-UF membrane process. The experimental results obtained from the pretreatment test showed that the optimum ferric chloride and PAC dosage for removal of organic matter applied for the coagulation and adsorption process was 50 mg/L as FeCl3 (optimum pH 5.5). Coagulation-UF pretreatment process was higher removal efficiency of organic matter, as also resulting in the substantial improvement of water flux of PRO membrane.

Pretreatment system of desalination process using seawater reverse osmosis(SWRO) membrane is the most critical step in order to prevent membrane fouling. One of the methods is coagulation-UF membrane process. Coagulation-UF membrane systems have been shown to be very efficient in removing turbidity and non-soluble and colloidal organics contained in the source water for SWRO pretreatment. Ferric salt coagulants are commonly applied in coagulation-UF process for pretreatment of SWRO process. But aluminum salts have not been applied in coagulation-UF pretreatment of SWRO process due to the SWRO membrane fouling by residual aluminum. This study was carried out to see the effect of residual matal salt on SWRO membrane followed by coagulation-UF pretreatment process. Experimental results showed that increased residual aluminum salts by coagulation-UF pretreatment process by using alum lead to the decreased SWRO membrane salt rejection and flux. As the salt rejection and flux of SWRO membrane decreased, the concentration of silica and residual aluminum decreased. However, when adjusting coagulation pH for coagulation-UF pretreatment process, the residual aluminum salt concentration was decreased and SWRO membrane flux was increased.

In this study, it is estimated that ceramic membrane process which can operate stably in harsh conditions replacing existing organic membrane connected with coagulation, sedimentation etc. . Jar-test was conducted by using artificial raw water containing kaolin and humic acid. It was observed that coagulant (A-PAC, 10.6%) 4mg/l is the optimal dose. As a results of evaluation of membrane single filtration process (A), coagulation-membrane filtration process (B) and coagulation-sedimentation-membrane filtration process (C), TMP variation is stable regardless of in Flux 2 m3/m2･day. But in Flux 5 m3/m2･day, it show change of 1-89.3 kpa by process. TMP of process (B) and (C) is increased 11.8, 0.6 kpa each. But, the (A) showed the greatest change of TMP. When evaluate (A) and (C) in Flux 10 m3/m2･day, TMP of (A) stopped operation being exceeded 120 kpa in 20 minutes. On the other hand, TMP of (C) is increased only 3 kpa in 120 minutes. Through this, membrane filtration process can be operated stably by using the linkage between the pretreatment process and the ceramic membrane filtration process. Turbidity of treated water remained under 0.1 NTU regardless of flux condition and DOC and UV254 showed a removal rate of 65-85%, 95% more each at process connected with pretreatment. Physical cleaning was carried out using water and air of 500kpa to show the recovery of pollutants formed on membrane surface by filtration. In (A) process, TMP has increased rapidly and decreased the recovery by physical cleaning as the flux rises. This means that contamination on membrane surface is irreversible fouling difficult to recover by using physical cleaning. Process (B) and (C) are observed high recovery rate of 60% more in high flux and especially recovery rate of process (B) is the highest at 95.8%. This can be judged that the coagulation flocs in the raw water formed cake layer with irreversible fouling and are favorable to physical cleaning. As a result of estimation, observe that ceramic membrane filtration connected with pretreatment improves efficiency of filtration and recovery rate of physical cleaning. And ceramic membrane which is possible to operate in the higher flux than organic membrane can be reduce the area of water purification facilities and secure a stable quantity of water by connecting the ceramic membrane with pretreatment process.