Study On The Pretreatment Process Of Tianjin Several Thousands Tons-Scale Seawater Desalination Project

Tianjin is a seashore city, which is the largest short of freshwater resource The design and proposed-built prqject-Tianjin TEDA Several Thousands Tons-Scale Seawater Desalination Project can effectively solve the problem of the future water demand for the Binhai New Area Compared with other seas, Bohai Sea quality is IV grade with the characteristic of low turbidity and temperature, higher organism, higher colloids, higher suspended solids and bacterial et al. This thesis will study the pretreatment technology and process for Bohai Sea in terms of its water quality. According to the seawater quality and the condition of Tianjin Binhai New Area, the study will concern on the unit process of enhanced coaguation, physical disinfection and membrane filtration. The removal effect of the turbidity, SS, COD_Mn and bacterial shall be studied for the purpose of confirming a best process scheme with flexible economy and stable operation for this project. Meanwhile, the study result will provide the design basis for this pretreatment project.Enhanced coagulation means together used the flocculants of FeCl₃, Poly-chloride (PAC) and Poly-acrylamide (FAM). The result of orthogonal shows that the best working condition is the dosage of FeCI₃, FAC and FAM are seperativdy 4 mg/L, 0.5mg/L and 0.3mg/L and the reaction temperature is 15°C. The main influent factors of them from the highest to the lowest are FeCl₃ dosage, FAM dosage, PAC dosage and temperature In this case, the removal of turbidity, COD_Mn and UV₂₅₄ are seperatively 96%, 40% and 19%.The results of UV, O₃, Pulse electrolysis and O₃-UV disinfection for the bacterial in the seawater shows that the reaction time is relatively long with single disinfection method. However, the result of bacterial removal with O₃-UV collaborative disinfection can up to 95.37% when the reaction time is 20min. And the result of orthogonal notes that the best operational condition is that the O₃ dosage is 2mg ? min/L, UV dosage is 12W/L, UV irradiation time is 10min, O₃ reaction time is 10min and the pH value is 8.83. The main influent factors of them from the highest to the lowest are O₃ flow, UV irradiation time, O₃ reaction time and the pH value.