L’ESPERTO RISPONDE – ACQUA

ACQUA

 

Domanda:

Quali sono le differenze tra Reverse Osmosis (RO), Ultrafiltration (UF), Nanofiltration (NF), and Microfiltration (MF)?

 

Risposta:

Reverse osmosis (RO), ultrafiltration (UF), nanofiltration (NF), and microfiltration (MF) membranes are used routinely to eliminate pathogens. MF membranes with nominal pore size equal to 0.2 µm effectively remove bacteria that are bigger in size than 0.2 µm, but generally, removal of viruses and endotoxins is poor (they are smaller than 0.2 µm), because the removal mechanism is sieving by physical exclusion. UF, NF and RO effectively remove viruses and endotoxins. However, the operating pressure of UF (2–8 bar), NF (7–15 bar) and RO (10–80 bar) is much higher than the operating pressure of MF affinity membranes (0.05–0.5 bar); this involves the use of pumps to obtain the same flow rate of affinity membranes. Moreover, because of occasional membrane defects, the viral removal efficiency is not always guaranteed.

Chromatography is generally limited by low capacity and long purification times because of the slow diffusion of the liquid when it enters and exits from the pores of the resin. Usually, this method is not as efficient because resins in the chromatographic columns become packed as a result of channelling and by-pass phenomena, which leads to different absorption and desorption rates, high cost and higher pressure drop in the packed beds (the liquid to be purified encounters higher resistance to access the active sites of the resins and the purification process is requires a long time to purify the liquid).

In contrast, affinity membrane filters are capable of capturing viruses and endotoxins at extremely higher flow rates with the efficiency typical of chromatography resins. They eliminate slow diffusion times typical of chromatography speeding up the purification processes and they operate at pressure lower (less than 0.1 bar) than the pressure required by UF, NF and RO processes. They seem to offer significant advantages in cost and time reduction over traditional pathogen treatment methods.

Up to now they are used to treat injectable liquids and their use in pharmaceutical and biotechnology downstream applications has been limited. However, they promise important future applications for the sterilisation of challenging liquids by combining the best characteristics of chromatography and traditional membrane filtration.