Found in many species of plants and often released into the soil and water when vegetation decomposes, tannins in water can be difficult to remove. These biomolecules give water a yellow or brownish tint and often make it taste bitter, but they are not a health risk. If you have tannins in your water, read on to learn more about this contaminant and ways to treat it from the Certified Water Specialists at US Water Systems.
If your water looks more like tea than the clean, clear liquid that it should, you may have a problem with tannin in the water. The distinct brownish color of a nice cup of hot Earl Grey tea or a glass of cold iced tea comes from tannin, a biomolecule found in plants – including tea leaves. While this color and its accompanying slightly bitter, astringent taste may taste great in tea, it isn't very desirable in water. The color makes water look dirty and can stain porcelain fixtures and laundry.
Tannins are found in many types of vegetation, including tea, berries, nuts, and many types of trees. When those plants decompose in the soil, they easily leach into the water that flows through them, making their way into surface water supplies and shallow wells. Along with the tannins are humic acid and fulvic acid, related "humic" substances – substances that are produced by decaying organic matter – which can enter the water supply. All of these substances have a similar impact on the water, changing the color and making it taste and smell bitter. Exactly which humic acids and tannins in water are causing the problem will vary depending on the plant life in a given area.
Tannins in water are not a health concern. Many of the foods that we eat every day contain various types of tannins, and they are in fact added to a number of beverages for their color and taste. In water, however, they are very undesirable.
Because there are a number of different tannins and types of humic acids, they can be very difficult to remove from water. Just because one treatment method for tannins in water works well in one location, that doesn't mean it will be effective a few miles away, where the vegetation may be different. Historically, styrene-based macroporous anion resin has been used to treat tannin water, but it doesn't always work. Acrylic-based resins have been used more recently and have produced better results. They are made with a macroporous structure that allows them to be regenerated more effectively.
In most cases, water treatment experts recommended that tannin water be treated by a water softener before being processed by a tannin removal system. The softener uses a cation media to removes hardness minerals and some metals, both of which can have a negative impact on the anion resin used to remove tannins. The water softener uses an ion-exchange resin that attracts positively charged particles, so it won't have any impact on the tannins in the water.
Tannins have a slight negative charge, which is why they can be treated with anion resins, which attract negatively charged particles. In this specialty resin, the tannin ions are exchanged for chloride ions. Since the resin can't really distinguish between tannins in water and any other type of negatively charged particle, it will also remove these additional ions. This typically means that alkaline ions are removed, which can cause a corresponding decrease in the pH of the water. Once the resins capacity for these ions has been reached, the pH will go back to its original level. Nitrates are also frequently removed by this type of resin.
This anion resin is typically regenerated (meaning that the accumulated tannins are removed and new chloride ions are made available for the ion-exchange process) with salt, and the resin will generally be brined at 10 lbs per cubic foot. Most importantly, this regeneration should be performed every two to three days, which will reduce the likelihood of organic fouling. Tannins tend to migrate into the inner matrix of the anion resin. Once this occurs, it is very difficult to regenerate the tannins from the resin.
In many tanning treatment systems, the tannin resin is mixed with softening resin. This reduces the amount of space required by the equipment and lowers the cost of the equipment. This type of design is not ideal, however, since the mixing of the media can cause problems. US Water does not recommend that cation and anion resin be mixed together in the same tank, and recommends softening first, followed by a tannin removal system.
One drawback to treating tannins in water with anion resins is the potential for the system to develop a fishy odor. This is caused by trimethylamine (TMA), which is an organic compound used to make the resin. Under high pH conditions, the TMA (even in small concentrations) can produce this unpleasant smell, although it should dissipate relatively quickly. When the resin is made with the proper post-treatment, it will generally lose its odor within a regeneration or two. It should be noted that a macroporous anion resin will generally clean-up faster and easier than gel type anion resins. If your water naturally has a high pH (greater than 8), it's more likely to release a fish odor, and there's really no good way to prevent this. Putting the resin through several regenerations and exhaustion cycles should reduce the smell.
Probably the worst case scenario will occur when there is both high pH and chlorine. As chlorine degrades the tannin resin, the combination of by-products and high pH can create a smell that may never completely go away. It can also be a problem with water treated with chloramines.
While tannin removal anion exchange resins are a popular way of removing tannin from your water supply, you need to realize that a tannin anion exchange system can use several hundred of dollars a year in salt and waste up to 80 gallons of regenerating water every other day. You may need to replace the resin in 5 or 6 years. We think there is a better way.
Recently, a technology called charged membrane filtration (CMF) has proven to be highly effective at removing tannin from water supplies. The US Water Pulsar system is truly "disruptive technology," that is ready to displace the established technology and shake up the industry. The Pulsar Charged Membrane Filter System can remove the following contaminants:
Charged membrane filtration is manufactured with Nano alumina fibers that have a zeta potential of 51 millivolts. A CMF cartridge retains bacteria, virus, cryptosporidium oocysts and even tannin because of this strong zeta potential. The electroabsorbative technology for water purification CMF media is engineered this 51 millivolt charge cover the entire volume and depth of the media.
Unlike mechanical filters that rely on pore size, the CMF technology literally secures the contaminant by absorbing it in a very real way. This allows for virtually zero pressure drop and high flow rates. If you compare the Pulsar CMF to ultrafiltration membranes, you will find dramatically higher flow rates with less pressure drop. The filters also have a long life and are easily replaceable.
The CMF media is manufactured from a naturally occurring element called boehmite, which has no known health side effects. In fact, boehmite has long been used as an additive to food products and digestive analgesics. Additionally, it has passed testing for NSF/ANSI Standard 42 and 61 for potable water and USP Class VI testing and endotoxin testing.
Overall, US Water recommends CMF over anion exchange softening due to cost and performance.
Oxidizing agents such as chlorine and ozone are sometimes also effective at breaking down tannins in water. A simple jar test will show the concentration and retention time required to oxidize the tannins. An activated carbon unit following the retention tank will remove the oxidant and adsorb any additional organic compounds in the water. It should be noted that some activated carbons alone may not have a significant amount of capacity for tannins, so consult your carbon manufacturer for the appropriate type of carbon. Reverse osmosis is another effective method of removing tannins.
When treating for tannins, it's important to remember that there is no method that is 100% effective. Call our Certified Water Specialists at 1-800-608-8792 to discuss which method for removing tannins in water might work for you. Once you find a water treatment that works for you, it's best to stick to that technology.