Study On Pretreatment Of Bohai Seawater Reverse Osmosis(SWRO)

Reverse osmosis(RO) has been widely used over the last 30years for desalination of brackish water and seawater due to the improvements of membrane technology. Controlling membrane fouling has always been a major problem in the process. But the conventional pretreatment, which is space consuming and costly can't ensure the quality of effluent fed to the RO membranes. Long-term operating experience at home and abroad proves microfiltraion a viable pretreatment for RO systems. Coagulation- microfiltraion process, a combination of coagulation and microfiltration (MF), is widely used in water purification because of the steady filtrate quality, easy automation and low operating pressure . In this study, PFS and PAC were used as the coagulant.The main purpose of this study is to investigate the feasibility of the process for coagulation-microfiltration to provide eligible influent to RO systems with suitable MF membrane by adjusting the operational parameters and the dosage of chemicals injected.In the first part of the experiment , a MF module with size of 0.1 μm made by MOTIMO was used. According to the experimental findings the quality of the filtrate produced by coagulation-microfiltration process is consistent and the 0.1 μm MF membrane can provide effluent with low SDI figure constantly below 2.5, the low turbidity below 0.1 NTU, and the Fe is be basically removed completely. The coagulation-microfiltration process with 0.1μm MF membrane is capable of treating seawater and producing suitable effluent to feed RO system without any further treatments. Meanwhile, the membrane fouling was also studied. A cleaning method with chemical cleaning and physical cleaning in special order was demonstrated useful.In the second part of the experiment, two kinds of flocculant (PFS and PAC) were researched for pretreatment of seawater. Because of the different characters of each flocculant, the effects are also different. From the general angle, the PAC is better than the PFS for the reasons that the removed efficiency of turbidity is above 95.9%, and the removed efficiency of SS is above 80.8%.