Clarification and prefiltration covers a wide range of filtration applications
Removing unwanted particles from the liquid components used to make APIs is only one application. Undissolved powders and solid impurities, for example, may be introduced to the process by product components. Removal of these particles is critical to the quality of the final product.
Particle control targets visible particulates and larger solids carried by a liquid. Clarification removes smaller particles that may be suspended in the liquid and causing a haze. Clarification may also be part of a prefiltration process designed to remove both particles and larger microorganisms to reduce the particle load on the more expensive membrane filters used downstream.
The filters marked "1" in the figure are the possible location of filters for all clarification and prefiltration applications. Only one filter housing is shown in this diagram, though multiple filter stages may be used in liquid streams with large particle loads.
Clarification and prefiltration is often performed using depth filtration media, with the filters trapping progressively smaller particles in the layers of media. Some applications will use membrane based filters to capture both small particles and larger microorganisms. Again, protecting the efficacy of the critical downstream membrane filters is the most important goal of prefiltration.
Removing at least some of the organisms that might be in the stream may be part of the prefiltration process. As described above, the final filters (see Sterilizing Filtration below) must be protected from premature fouling by an excess of particles or bacteria. Bioburden Control filters are designed into the system to remove most, but not all bacteria. The sterilizing filters are then able to perform their function for an entire batch of product without fouling and causing undue difficulties with batch processing.
The housings marked "2" in the figure are in place to reduce the amount of bacteria and prevent premature fouling of the final, sterilizing filters. Bioburden reduction filters are usually membrane-based filter with pore sizes of 0.45μm to 0.80μm. This filter captures the bulk of the microorganisms, though not all.
When bacteria must be removed, before final packaging or to protect an intermediate process, this filter is chosen to remove whatever bacteria may be present in the product.
Filters used for this final filtration step are almost always membrane filters with an effective pore size of 0.22µm or 0.10µm with the pore size chosen based on the organisms that have been identified in the customer’s system. Sterilizing filters are integrity tested before and after use to assure that the filter has been installed properly and has not been damaged in any way.