Studies On Seawater Desalination By Outside-in Ultrafiltration Membranes

The membrane processing technology has been widely applied in water treatment profession. As the seawater pretreatment prior to reverse osmosis membranes, ultrafiltration is simple, safe and stable, compared to conventional processing technology. Now ultrafiltration has been applied in Europe, American and Gulf region, but it is still the start stage in our country. When ultrafiltration is used in actual project, we must carry on the pilot study, aiming at different water quality, to guarantee the feed water condition and stability of reverse osmosis membranes.This pilot study selected three kinds of outside-in ultrafiltration to experiment on the southeast high turbidity seawater in our country. Through three stages experiments of stable running, parameter optimization and strengthened destructiveness, We analyze the following several aspects: the condition of high turbidity seawater quality; the permeate quality of ultrafiltration and removing rate of pollution matter; the attenuation condition of entire and cyclical stage and recovery after backwash; the comparison of three ultrafiltration material and running craft; the influence factors of permeate SDI.The pilot study indicates: the temperature and pH of ultrafiltration permeate don't change more compared to feed water. Ultrafiltration has 100% removing on turbidity and bacteria, and 30%- 90%, 80%- 95%, 0%- 80% removing on silicon, iron and COD. In membrane pollution process, A prevents the gelatin coming into being better by frequent small dosage NaCIO backwash; The B double cortex structure has caused the TMP large and intensified the membrane hole block; The C immersion type membrane has controlled the gelatin difficultly and the membrane pollution is serious. When A directly processes seawater, the principle of ultrafiltration causes the same effect of pollution matter removing with B and C. The double cortex membrane and the immersion type craft are all not suit the pretreatment of high turbidity sea water.This article also studies and analyzes the influence factors of permeate SDI: the SDI of permeate are all below 3; the way of cross flow and the low flux parameter can alleviate the pollution matter of permeate, and reduces its SDI value; SDI has better value when pH is between 6-8 and temperature is lower than 30℃; the pollution of membrane caused by organic matter can results SDI high; when the concentration ofpolymerization iron sulfate is bigger than 21mg/L or the concentration of NaClO are bigger than 6mg/L, it will cause SDI increase rapidly.