How to Select AS Acid-resistant and BS Alkali-resistant NF

The same cut-off does not mean the same operating window

AS and BS both list a reference cut-off of 200 Da, but their chemical and operating limits differ. AS targets acidic process streams; BS targets alkaline streams. Selection must consider acid or base identity, concentration, temperature, exposure time, oxidants, metals and the materials of the complete system.

Compare the published limits

AS lists maximum pressure of 55 bar, operating and cleaning temperature up to 40°C, operating pH 0–12 and cleaning pH 0–13. BS lists maximum pressure of 40 bar, temperature up to 50°C, operating pH 3–14 and cleaning pH 2–14. Both list a maximum pressure drop of 1 bar and pressure ramp below 0.7 bar/s.

Reference flux is 25 LMH for AS and 30 LMH for BS, with reference rejection of 96%. Test conditions are 2000 ppm MgSO4 or 5% glucose at 15.5 bar, 30°C and pH 7, with approximately ±20% flux variation. These neutral test values are not performance guarantees for concentrated acid or caustic feeds.

Test chemical compatibility and recovery

Sulfuric, hydrochloric, phosphoric and acetic acid streams are candidates for AS evaluation. The source discusses 20% NaOH and 10% KOH in relation to BS; these references do not establish suitability for every mixed process liquor. Confirm composition and exposure conditions with the supplier.

Address free chlorine and other incompatible oxidants before operation. Test realistic concentration cycles and cleaning, then assess retained product quality, recovered liquor quality and long-term membrane stability before engineering scale-up.