Source Water Pretreatment in the Bottled Water Industry
Source waters typically contain a number of contaminants that may affect the purity and quality of bottled water. Failure to effectively treat these contaminants may lead to contaminated product water, costly product recalls and subsequent loss of customer trust. A successful bottling operation will do everything possible to avoid such problems.
The U.S. FDA and the bottled water industry require certain tests that impact source water characteristics, including: a complete water analysis when the plant starts up (and once a year after that); monthly tests for bacteria; ozone at start-up of every product run and twice per product per day; and a pH level check every hour during processing, daily if not processing.
Water contamination varies according to the sources from which the water is taken. Spring water and well water present different treatment challenges. In this article, we will look at water sources such as spring water, well (or borehole) water, reverse osmosis (RO)-processed water and distillation-processed water.
Spring water is defined as water that flows naturally to the earth’s surface from an underground formation. Contaminants typically found in spring water include turbidity, nitrates, total dissolved solids (TDS), bacteria, bromate, and iron or manganese.
Spring water-specific pretreatment options include multimedia filtration down to 10 microns, depth filtration down to 5 microns, ultraviolet (UV) units and depth filtration down to 1 micron absolute.
If ozone treatment is to be used after typical treatment, additional techniques may be needed to remove iron or manganese from the source water. In some cases of heavy bacterial contamination, chlorination of water and then chlorine removal by carbon filtration would be necessary.
Well Water/Borehole Water
Well water, or borehole water, is defined as water taken from a hole that has tapped (drilled or bored) into the water of an aquifer. Contaminants typically found in well water/borehole water include nitrates, TDS, bromide, bacteria, and iron or manganese; pH problems are also typical.
Recommended pretreatments include: multimedia filtration, aeration, depth filtration down to 1 micron and UV application. As with spring water, if ozone treatment is to follow, other pretreatment options may be required to remove iron or manganese from the source water. In some cases in which heavy bacterial contamination is reoccurring, chlorination of the well and carbon filtration may be required. If bromide levels are too high—generally over 5 ppb—ozonation of the water may not be possible. In those cases, UV units followed by 1-micron absolute filtration are required.
Correction of pH levels may be needed for very low pH values from wells. Many low pH conditions result from carbon dioxide gas in the water. Aeration will drive this out of the water. In some cases, sacrificial calcium carbonate filters successfully raise pH values.
RO-processed water has been purified by the RO process and meets the definition of purified water found in the United States Pharmacopeia.
In most cases, pretreatment of the feedwater prior to the RO system will be required. Contamination includes bacteria, silica, hardness, turbidity, iron and manganese, chlorine (found in municipal water supplies) and aluminum.
Recommended pretreatment includes using UV systems on well or spring source waters to help prevent “biofouling” of RO membranes. Turbidity can generally be reduced by media filtration, followed by 5-micron filtration. A carbon filter is required with chlorinated municipal source waters to remove chlorine to prevent destruction of the RO membranes. Special carbon or oversized carbon units will be required if chloramine is present in the source water.
Hardness is typically reduced by softening incoming source water. A twin alternating automatic regenerating system is preferred to prevent any hardness bypass to the RO unit. Antiscalant chemical injection can also be used to keep hardness minerals and silica in suspension to prevent membrane scaling. Silica can be a problem if it is over 20 ppm in source water. If levels are high, the recovery rate of the RO system can be changed or the incoming source water pH lowered by acid injection. The current preferred method is to inject an antiscalant solution into the source water to keep the silica in solution until it goes out of the system in the reject drain water stream. In this case, a good product flush system should be installed on the RO system.
Iron and manganese must be removed from source water by pretreatment methods such as aeration, chlorination or softening, or iron and manganese can be kept in the solution with the use of antiscalants.
Distillation-processed water is water that has been vaporized and condensed, and meets the definition of purified water in the U.S. Pharmacopeia. Contaminants that can cause problems during the distillation process and should be addressed prior to source water entering the distillation system include chlorine, high TDS, hardness, silica and high chloride levels.
During pretreatment, chlorine should be removed with carbon filtration before it enters the distillation equipment; otherwise, the chlorine will attack the distiller’s internal parts, which are made of stainless steel. Special carbon or oversized carbon units will be required if chloramine is present in the source water.
A twin alternating automatic regenerating softener is recommended to remove hardness before source water enters the distiller because the hardness will cause scaling problems. High TDS levels may dictate the use of an RO unit before distillation. The source water must be tested for silica levels when large-sized distillers are used. High silica levels may result in silicate formations inside the distiller.
It is critical to properly identify source water contaminants in a bottled water operation to ensure that they are eliminated prior to bottling. By effectively treating these contaminants, bottlers of varying source water can avoid costly problems and stand behind high-quality products.