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.