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When designing a reverse osmosis system using Hydranautics reverse osmosis membrane elements, the following general guidelines should generally be followed. For applications exceeding these guidelines, please consult with Hydranautics for specific advice.
Average water flux and allowable annual water flux degradation percentage
water source | SDI | Water flux - gfd | Water flux decline - percentage/year |
Surface water | 3~5 | 8~14 | 7.3~9.9 |
well water | <3 | 14~18 | 4.4~7.3 |
Reverse osmosis product water | <1 | 20~30 | 2.3~4.4 |
Allow for an annual increase in salt permeability percentage.
Membrane type | Membrane type abbreviation | Increased salt permeability – percentage/year |
Ultra-low pressure polyamide composite membrane | ESPA1, ESPA2, ESPA3, ESPA4 | 3~17 |
Low-pressure polyamide composite membrane | CPA2, CPA2-HR, CPA3, CPA4 | 3~17 |
Low-pollution polyamide composite membrane | LFC1-365, LFC1, LFC2, LFC3 | 3~17 |
Seawater desalination membrane | SWC1, SWC2, SWC3, SWC4 | 3~17 |
Energy-saving polyamide nanofiltration membrane | ESNA1, ESNA2, ESNA-LF | 3~17 |
Maximum feedwater flow rate and minimum concentrate flow rate in each pressure vessel.
Membrane diameter – inches | Maximum water flow rate – gallons per minute (tons per hour) | Minimum concentrate flow rate – gallons per minute (tons per hour) |
4 | 16 (3.6) | 3 (0.7) |
6 | 30 (8.8) | 7 (1.8) |
8 | 75 (17.0) | 12 (2.7) |
8.5 | 85 (19.3) | 14 (3.2) |
Saturation limit of sparingly soluble salts in concentrated water
Salt | Saturation value - % |
CaSO4 | 230 |
SrSO4 | 800 |
BaSO4 | 6000 |
SiO2 | 100 |
Saturation index limit
condition | LSI value |
LSI and SDSI without scale inhibitor | ≤ -0.2 |
LSI and SDSI when using sodium hexametaphosphate as a scale inhibitor | ≤ 0.5 |
LSI and SDSI when using organic scale inhibitors | ≤ 1.8 |
