Filters in Bottled Water Production and Packaging
Whether from a spring or municipal water system, incoming water will have particles suspended in it that should be removed to protect system and product quality. The figure shows multiple filters (housings 1, 2, 3 and 5) that are in place to remove particles larger than 1 micron and keep downstream processes running smoothly.
These filter functions are performed using depth filtration products. The first filters remove sediment and other suspended particles. Trap filters (housings 2, 3 and 5) remove particles that may be released by equipment, such as sand particles from the multi-media filter, carbon particle after the activated carbon vessel or particles from fractured deionizing or softening resin beads in the resin trap filter.
Prefiltration for the RO system (housing 3) is also performed using depth filter media. Most systems manufacturers recommend removing particle larger than 5 microns to assure the life of the RO membranes. Some operators choose to remove even smaller particles to extend membrane life and reduce the need for system cleaning.
There are many possible bacteria and molds that could enter the process, but all can be removed just before packaging using membrane filters. Organisms can enter the bottle from two directions. The water itself can carry organisms. Even spring water from an underground source has some bacteria. The bottles can also bring organisms from the environment or from the water used to wash and rinse them.
Housings marked "6" in the figure are in place to capture most, though not all, of the fine particles and organisms that are in the product water or package wash/rinse water just before packaging. The filter is usually a membrane filter with pore sizes of 0.45µm to 0.65µm. This filter captures the bulk of the organisms and protects the critical final filter from being overloaded and fouling prematurely.
The final, sterilizing filter for the water (housings marked "7") captures all remaining bacteria. The membrane filters most often have pore size ratings of 0.22µm, though some operators choose to use 0.10μm pore size filters. This filter is the most critical in protecting your final product from possible contamination just before packaging.
Water may be stored in a tank system for distribution to additional treatment steps or for staging before packaging. Filtration acts as a critical contamination control step protecting your water from particles ranging in size from dust to particles as small as 0.03 microns. For bottled water operations, the vent filters act as a barrier to prevent airborne contaminants such as dust, bacteria and mold from entering the tank as the water is pumped to downstream operations.
Hydrophobic membrane filters are used for this filtration application. The hydrophobic nature of the membrane prevents water droplets from collecting on and wetting the membrane, which would block the flow of air and lead to tank failure. Tank vent filters with 0.22µm pore sizes are usually used because of their ability to block bacteria from entering the tanks.
Some operators use process gas to reduce the oxygen available in packages and remove one element that might support bacterial growth in packaged water. However, as with the water used to wash and rinse packages, the gas could carry organisms into the packages. Using hydrophobic membrane sterilizing filters similar to those used for vent filtration will prevent bacteria from entering the packages with the process gas.