Study On The Pretreatment Of Desalination By Reverse Osmosis With Coastal Waters Of Bohai Sea

Reverse osmosis (RO) is one of the main processes for the seawater desalination. Comparing with other desalination processes, RO has many distinct advantages in that the energy consume rate is low, for there is no energy-intensive phase change and high efficient energy recovery equipments are used in RO process. There will be some large-scale seawater desalination projects to be carried out along the coast of Bohai gulf, but the pretreatment technologies of seawater are the bottlenecks of the RO application. Accordingly, it is very important to carry out the studies on seawater pretreatment. Considering the seawater polluted seriously in Bohai sea, in order to make seawater up to the inlet grade of RO process, we perform the pre-oxidation and coagulation-flocculation jar test and study the process of coagulation-flocculation, filtration and ultrafiltration(UF).In the process of seawater pre-oxidation and coagulation-flocculation, we investigate the effects of the additive dosage on the flocculation with different kind of pre-oxidants and coagulants and process parameters on the flocculation. Results show that water temperature is an important factor in the process of coagulation-flocculation and potassium ferrate(VI) removes alga, COD and turbidity of seawater effectively. When potassium ferrate(VI) is used only, the alga removal rate is more than 70%,which is higher than the rate as ferric chloride is used only. While ferric chloride combined with potassium ferrate(VI), the alga removal rate can get more than 80%. At the sometime, we find that K₂FeO₄ remove the alga rapidly, five minutes later after K₂FeO₄ addition the alga removal rate can get up to 40-60%. K₂FeO₄ is a strong oxidant, it can raise the COD_Mn remove rate of seawater in the process of flocculation to a great extent. At the level of 5 mg/l K₂FeO₄, the COD_Mn removal rate can attain 40%.NaClO, KMnO₄ and K₂FeO₄ have obvious effects on oxidation and coagulation. At small quantity NaClO and K₂FeO₄ have the same effect on alga removal. When the...