Pretreatment ro membrane

  Permissible Feed Water Quality For Reverse Osmosis Systems   Number Item Allowed value Unit Remarks 1 Turbidity 1.0 NTU The maximum allowable turbidity is 1.0 NTU, with a target value of less than 0.2 NTU. 2 Silt Density Index (SDI15) 5.0 NA The maximum allowable SDI15 is 5.0, aiming for a value lower than 3.0. 3 pH 2~11 NA The permissible pH range for the influent varies depending on the membrane type. Additionally, the influent temperature may also affect the allowable pH value. 4 Temperature 1~45 ℃ 5 Free Chlorine 0.1 mg/L The influent should not contain oxidants such as chlorine, permanganate, or other strong oxidizing agents. 6 TOC(以C计) <5 mg/L The TOC level should be below 5 mg/L. It is important to note that TOC, Chemical Oxygen Demand (COD), and Biochemical Oxygen Demand (BOD₃) serve only as reference parameters due to the complexity of organic compounds. 7 COD(以O₂计) <15 mg/L 8 BOD₃ (以Oz计) <10 mg/L 9 oil 0 mg/L The presence of oil should not be detectable in the influent. 10 Ferrous Ion(Fe2+） <4 mg/L The allowable concentration of ferrous ions is below 4 mg/L. For water with dissolved oxygen below 0.5 mg/L and a pH below 6, this limit applies 11 Ferric Ion(Fe3+） <0.05 mg/L The allowable concentration of ferrous ions is below 4 mg/L. For water with dissolved oxygen below 0.5 mg/L and a pH below 6, this limit applies 12 Manganese Ion(Mn²*） <0.05 mg/L The allowable concentration of ferrous ions is below 4 mg/L. For water with dissolved oxygen below 0.5 mg/L and a pH below 6, this limit applies 13 Aluminum Ion(Al³+) <0.05 mg/L The allowable concentration of ferrous ions is below 4 mg/L. For water with dissolved oxygen below 0.5 mg/L and a pH below 6, this limit applies 14 Calcium Carbonate(CaCO₃) LSI<2.0 NA LSI < 2.0 NA With the addition of scale inhibitors, the highest allowable LSI value is 2.0. 15 Calcium Sulfate(CaSO₄） <400 % (1) Different concentrations, pH values, and temperatures have varying effects on the precipitation and deposition of different sparingly soluble salts in water. If the saturation level of a sparingly soluble salt exceeds 100%, it indicates scaling on the concentrate side.(2) The values on the left indicate the maximum allowable saturation level under measures such as adding scale inhibitors. 16 Barium Sulfate(BaSO₄) <10000 % 17 Strontium Sulfate(SrSO₄） <1200 % 18 Calcium Fluoride(CaFz) <5000 % 19 Surfactants Care should be taken when selecting cationic or amphoteric surfactants 20 Silica (SiO₂) Silica should not precipitate on the concentrate side Generally, the maximum allowable concentration is 100 mg/L in the absence of scale inhibitors.