Flow measurement for WFI loops: Preventing biofilm development

WITHIN WATER for Injection (WFI) loops, the potential for biofilm development - formed by the accumulation of trace bacteria - is a critical threat that is primarily caused by laminar flow and the presence of dead zones in the pipework. 

Undetectable, trace amounts of bacteria can enter a WFI loop through microscopic leaks or cracks in the system, or contamination from maintenance. Given the conditions necessary for their growth, including microscopic traces of nutrients, temperature fluctuations, or insufficient cleaning practices, this is how trace bacteria can develop into a biofilm.

Therefore flow metering and control are crucial to prevent biofilm accumulation.

The challenge for Coriolis meters

Traditionally, Coriolis sensor technology has been used within WFI loops to measure flow. A Coriolis meter typically integrates a bent tube because a curve enhances the twisting effect, which increases the precision of mass flow measurement.

The problem is that the curves within a typical Coriolis meter can cause dead zones and low flow areas, which over time can lead to biofilm build-up. Moreover, the bends in the tube also cause a pressure drop. This decreases the flow and subsequently diminishes the potential of washing away trace bacteria before it can develop into a biofilm. 

Pump speed could be raised to optimise flow, but this will increase energy demand and reduce the life of the pump, as well as raising the potential for maintenance. However, if pump speed becomes too fast, this could also result in pressure drops

Surface Acoustic Wave technology

An alternative flow measurement system for WFI loops is based on Surface Acoustic Wave (SAW) technology. With this approach, a flow meter generates surface acoustic waves that travel through the fluid. Calculating the time differences of the waves proportional to the flow, a SAW technology flow meter, like Bürkert’s Type 8098 FLOWave, can measure real time volumetric flow rate, cumulative volume, and flow velocity, as well as temperature – all vital indicators of conditions crucial to preventing biofilm development. 

The key advantage for WFI loop design is that SAW technology utilises a straight tube, preventing dead zones or the potential for pressure drop, which minimises the potential for bacterial growth. SAW technology also achieves this without any sensors in the flow, further decreasing the potential of biofilm development. Instead, the ultrasonic waves travel along the surface of the tube, with the sensors positioned on the external surface. 

The 316L stainless steel internal surface of Bürkert’s FLOWave flow meter has an average roughness (Ra) rating of <0.4 µm, making it ultra smooth. This ensures there are no microscopic pits or imperfections where biofilm can grow. The ultra smooth surface also helps FLOWave achieve CIP/SIP compatibility, and the design conforms with the necessary pharmaceutical standards, including an FDA certificate of conformity, and certification of compliance ASME BPE.  

Damien Moran is business development manager for Pharma and Biotech at Bürkert

For more information: 

www.burkert.co.uk

Tel: +44 1285 648720