Bottled water is produced in several formats with the production processes different depending upon the source and the classification.
Spring Water: As the names suggests, water comes from an untreated underground source. By defi nition, the water may only have minimal treatment, however processing must be done on the water to assure removal of harmful microbes and since no bacteriostatic agents can be added.
Mineral Water: Spring water containing at least 250 parts per million total dissolved solids (TDS). No minerals may be added to this water to create the TDS. The term “mineral water” is sometimes used to mean any bottled carbonated water.
Sparkling Water: Also referred to as club soda, soda water, sparkling water or seltzer water, is water into which carbon dioxide gas under pressure has been dissolved that causes the water to become effervescent. The water used for the carbonation is typically purified by reverse osmosis.
Purified Water: Water may come from any source, but most typical is municipal or well water. The water is typically processed through reverse osmosis and then some minerals are added back for taste.
Distilled Water: A version of purified water where condensed steam is collected on a cool surface. Most contaminants do not vaporize and therefore do not pass into the distillate, removing nearly 100% of all impurities.
PURIFICATION PROCESS
The spring water bottling process requires treatment that delivers satisfactory aesthetics as well as a product that is microbiologically safe. Visible clarity is essential and thus filtration down to 20 micron or less is required. At this point, the water can undergo exposure to ultraviolet light, treatment with ozone, filtration by a microbial rated microfiltration membrane or a combination of these processes.
Often UV is used in conjunction with membrane products such as ZTEC™ WB that have documented retention of Psuedomonas aruginosa, which is the common indicator for a 0.2 micron filter in this application. Prefiltration must also be part of the system design in order to protect the membrane filters. One to five micron Polypropylene depth or pleated filters are commonly used.
Large diameter cartridges such as the High Flow are becoming more commonplace due to the simplicity of design of a single cartridge as well as the smaller footprint of the vessel. If ozone is used in the process and will contact the filters, the use of an all-fluoropolymer filter such a Citadel is required due to the risk of damage to filters composed of other polymers such as polypropylene and PES.
Reverse osmosis is the central component of a purified water process. The source water will determine the level of prefiltration required, with the typical goal to have water with a Silt Density Index (SDI) of 4 or less. As with most prefiltration designs for reverse osmosis systems, the filter commonly used are polypropylene depth filters such as Stratum. Similar to spring water filtration processes, the large flow demands of purified water processes are favoring the use of large diameter filters such as the High Flow.
CASE STUDY
A large multinational beverage company had an installed system to produce sparkling water utilizing Pall High Flow cartridges.
The system was designed to use a 20 micron followed by a 10 micron, both 60" in length, which then fed into a UV light followed by a 0.2 micron membrane filter. Clay, sand and some organic materials were causing high turbidity and subsequent short life on the membrane filters. The incoming water was between 46°F–54°F (8°C and 12°C), giving the water a viscosity of approximately 1.6 cp. Coupled with the system flow of 420 GPM (1600 LPM), the large diameter cartridges provided an ideal design, requiring the use of a single vessel for each prefilter.
Standard cartridge design would require the use of at least 28 cartridges to meet the flow. In an attempt to improve the process and reduce filtration costs, the end user agreed to evaluate the Graver High Flow cartridges.
Rather than a direct substitution, the end user switched the 10 micron with a Graver High Flow 3 micron which was protected by a 20 micron High Flow. As expected, the 3 micron resulted in lower turbidity and thus offered better protection to the 0.2 micron membrane filter, yet despite the use of the more efficient filter, overall filtration costs decreased.
The successful change lead the end user to subsequently evaluate the use of a 1 micron Graver High Flow followed by a 1 micron. Again as expected, the 1 micron offered yet further life improvement of the 0.2 micron while still providing overall cost advantages from the original system design using Pall cartridges.