Study On Process Optimization And Technolgy Design For Ultrafiltration Seawater Desalination Pretreatment

Reverse osmosis?RO?desalination has become an important strategy measure for coping with the stress of global water crisis.Since ultrafiltration?UF?showed high removal efficiency for SS and turbidity and provided consistent good quality water to RO,it has replaced conventional pretreatment method such as sand filtration and been widely accepted as the preferred pretreatment technology for seawater desalination.However,problems like membrane fouling still seriously influenced the application effect of UF pretreatment technology.Thus,carrying out the research of UF process and hybrid technology system for seawater desalination pretreatment is conductive to optimize the operating parameters and increase the performance during the operation,which will produce far-reaching significant for the stability of RO desalination plant.UF pretreatment technology for seawater was studied in this research.The influence of seawater on membrane flux was investigated.The recovery effect of transmembrane pressure using different physical cleaning technology was analyzed.The membrane resistance and fouling rate under different operation conditions was studied in this test.Results showed that seawater quality and temperature can bring significant effect on UF flux.Air washing and air water backwashing has been proved as the most preferred physical cleaning technology as air water backwashing can achieve the 100%recovery effect of TMP.Compared with dead-end filtration,the membrane resistance of cross-flow filtration only decreased 2%-3%.UF showed a better performance under low flux operation condition,results showed that when the flux was 40L/?m²·h?,long-term operation stability can be reached at 20?with the specific flux?SF?stabilized at 14.07 L/?m²?h?m H₂O?and membrane fouling rate?K?at0.76 m^-1.The treatment efficiency and stability of short process UF pretreatment technology was studied in this test.Results showed that at the flux of 70 and 80L/?m²·h?,UF provided water with consistently low turbidity?<0.2NTU?and stable silt density index(SDI₁₅<2.5)in the pilot test and the TMP and SF of membrane remains stable.Better filtration performance and stability can be achieved with high quality seawater with the TMP ranged from 27.5-51.4kPa and the SF ranged from14.33 to 18.67 L/?m²?h?mH₂O?.Hybrid pretreatment systems comprised coagulation/sand filtration and UF were studied in this pilot-scale experiment.The operation conditions of UF was optimized and the performance of different hybrid systems was estimated in the test.Results of the research showed that hybrid pretreatment can effectively reduce the TMP and increase the SF of UF.By comparing different pretreatment systems,it can be found that the best treatment effect appear in coagulation/sand filtration/UF system,and the coagulation/UF showed better performance than the sand filtration/UF system.The increase of SF in these hybrid systems is 43.1%?24.6%and 11.3%while the decrease of membrane fouling rate is 50.6%?36.5%and 21.4% respectively.