Sterile vent filtration in ozonated water tanks

Ozone used to sanitize pharmaceutical water systems can degrade conventional vent filters. Our field studies show that Emflon™ HTPFR filters maintain integrity and exhibited no material deterioration after prolonged exposure to ozonated water systems, demonstrating improved resistance to oxidative conditions and extended service life compared with standard polypropylene-based vent filters.

Introduction

Pharmaceutical water systems require protection from particulate and microbial contamination during storage and distribution. This is achieved through measures such as hot-water storage or ozone sanitization of purified water systems. Ozone is widely used as an antimicrobial agent in ambient-temperature water storage and distribution systems and may also be considered for some WFI applications.

Water tanks are typically fitted with sterilizing-grade vent filters to allow air exchange during filling and emptying while preventing microbial ingress. In ozonated systems, ozone can accumulate in the tank headspace and vent housing due to off-gassing from the water. Exposure to ozone and elevated temperatures can degrade polypropylene components commonly used in vent filters, leading to embrittlement and reduced service life.

We developed Emflon HTPFR filters to provide a longer vent filter service life in applications that involve a highly oxidative environment. Emflon HTPFR filters contain polytetrafluoroethylene membrane and have been developed with a special support and drainage material made from polyphenylene sulfide (PPS) which is more robust in oxidative environments. In addition, the polypropylene hardware used for Emflon HTPFR filters has been optimized to have greater resistance to oxidation.

To confirm the suitability, compatibility, and resistance of Emflon HTPFR filter cartridges on ozonated water tanks, two on-site investigations were conducted with Emflon HTPFR filters as the sterile vent filter on different pharmaceutical water system tanks, and with ozone for sanitization.

Study 1: Water tank with ambient temperature and 100 ppb ozone

In the first study, we used 10-inch Emflon HTPFR filters as sterile vent filters for pharmaceutical water tank systems with 100 ppb ozone as a disinfectant in the water. The maximum air flow rate for this application of venting WFI tanks at ambient temperature was calculated to 12 m³/h.

After 6 months (mo), the Emflon HTPFR filter passed the water intrusion integrity test (WIT), and showed no deterioration in the condition of the hardware, support, drainage or media layers following a detailed visual inspection (data not shown).

Study 2: Water tank with up to 40°C and 20 to 100 ppb ozone

In a second study, we used two Emflon HTPFR filters for sterile venting of a pharmaceutical water system with tank volumes of 800 and 8000 L. The estimated working volume in these applications was approximately 14 m³/d at atmospheric pressure.

We monitored the ozone concentration, which was between 20 and 100 ppb in the water during the usage time, with an adjustment of the ozone concentration overnight.

After 25 weeks (wk) of constant venting work in an ozonated environment, both Emflon HTPFR filters passed the water intrusion integrity tests and showed no deterioration in the condition of the hardware, support drainage, or media layers (Table 1).

Table 1. Investigation results, study 2*

* Project B-EU-CH-1341, Report no. B-EU-CH-1341-IT.

Summary and recommendations

The results demonstrate that Emflon HTPFR filters have a higher degree of resistance to oxidation than Emflon II and Emflon PFR filters in vent filter systems on ozonated water tanks. Emflon HTPFR filters can be considered optimal as sterilizing-vent filters in water systems operated with:

• 100 ppb ozone in water at ambient temperatures for a minimum of 6 mo of use.
• 20 to 100 ppb ozone in water at temperature of 20°C to 40 °C for a minimum of 25 wk of use.

For water charged with significantly higher ozone concentrations or hot water installations that use ozone in addition as disinfectant, the use of Emflon PFA filters (which provide full resistance to ozone) should be considered for use.

In addition to temperature and ozone concentration in the water, it is important to consider that specific installation and plant properties, as well as other operating parameters like filling and drainage rates, head volumes and steaming cycles in a water plant and tank, may have further influence on the service life of sterile vent filters. Furthermore, the water quality can influence the service life of the filters, as the half-life of ozone and therefore the concentration of this disinfectant is dependent on the water quality.

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