Study On Coagulation-Air Floatation Process For Seawater Desalination Pretreatment

According to the characteristics of Bohai Sea's water quality, the experimental study of coagulation-air flotation for seawater desalination pretreatment was made and the optimal process parameters were summed up, using a 5.0 m /h pilot test platform. Furthermore, the strengthen removal organic matter also has been studied. The researches show the results as follows.(1) The optimal operating parameters of the FeCl₃ mixture coagulant are as follows: FeClmixture dosage 15²0 mg/L, chlorine water dosage 3.0 mg/L, recirculation ratio 15%. on these best conditions, the removal of turbidity is 90%, CODMn 16.4%, TOC 20.0%. The optimal operating parameters of the PACl coagulant are as follows: PACl mixture dosage 6¹0 mg/L, chlorine water dosage 3.0 mg/L, recirculation ratio 15%. on these best conditions, the removal of turbidity is 89.2%, CODMn 29.4%, TOC 25.1%.(2) Using chlorine water + FeCl₃ mixture, the removal rate of organic matter under the strengthening coagulation process increases 5%⁸% than under the conventional coagulation process. When using powdered activated carbon at the same time of using chlorine water + FeCl₃ under the strengthening coagulation, the removal rate increases 6%¹0%. Using chlorine water + PACl, the removal rate of organic matter under the strengthening coagulation process increases 5%¹2% than under the conventional coagulation process. When using powdered activated carbon at the same time of using chlorine water + PACl under the strengthening coagulation, the removal rate increases15%²2%.(3) The recommended pretreatment process for seawater desalination is presented: Raw seawater– pre-chlorination (2.5⁴.0mg/L)– PACl coagulation (6¹0mg/L) - floatation (recirculation ratio 15%) - UF. If organic pollution is serious and enhanced removal is necessary, the method of dosing powdered activated carbon to mixing-pool could be used. The per ton of water treatment estimate cost is 0.35 yuan/m3 .