Multi Media Tannin

Tannin Removal Media is a specialty purpose ion exchange resin designed to remove tannins, organic color and other naturally occurring organics including organo-metallic complexes (such as heme iron) from drinking water. In areas with organic contamination such as old river beds, swamps, non-deep underground aquifers and in downhill areas water source may be contaminated with organics, making a tea-like water color.

How Tannin Filtration Media works:

Tannin removal media works via ion exchange. Resin is intended to be used as an organic trap in a stand-alone unit in conjunction with other ion exchange processes, such as water softening or demineralization. Sodium chloride is generally preferred for regeneration for reasons of cost and efficiency. When available, sea water can be used quite effectively.

Tannin removal is an application that some dealers have felt uncomfortable tackling. Tannins, until several years ago, were treated with standard strong base macroporous anion resins manufactured with styrene and divinylbenzene. This type of resin worked well in some areas but failed in other areas. Over the last 5 to 10 years resins have come into the residential water market that have been more successful and have made this water treatment problem more attractive to the water treatment dealer, like Integrity Water Inc.

It is usually recommended that the water be softened prior to the tannin removal unit. The softener removes hardness and metals (like iron) that might otherwise foul the anion resin. Tannins will pass through softening (cation) resin without any detrimental effects. Hardness levels greater than 10 grains passing into a tannin removal unit may precipitate calcium carbonate, which is a white floc that can restrict flow in the system and blind exchange sites on the resin. Metals like iron also can foul the anion resin, reducing the anions' ability to remove tannins. Cleaning methods for these foulants will be discussed later.

Tannin Removal

Tannins are large molecular weight organic compounds. They are formed through the decomposition of plants and, to a much lesser degree, animals. These organics are generally found in surface waters or shallow wells. There are two primary categories in which tannin fall: Humic acid and Fulvic acid. These are simplified structures of very large molecules. Gallic acid, guaiacyl, syringyl and cresylic moieties are the building blocks of these organic molecules (Kunin, 1986). The structure of the tannin will vary from location to location, depending on the vegetation in the area. Tannins can also cause a yellow to dark tea color in water and may impart taste and odor. Tannins are not directly regulated by a governmental agency, however there is a secondary drinking water standard of 15 alpha units for color. A secondary drinking water standard is not federally enforced. Tannins are not a health issue; however, they are aesthetically unpleasing.

Tannins can be difficult to remove from water. One treatment method may be effective in one area, but it may not be totally effective 10km down the road. It is entirely dependent on the vegetation in a given area. Styrene-based macroporous anion resin has long been used to remove tannins from water. This type of resin worked well in some areas but poorly in other areas. More recently acrylic-based resin have emerged on the market and are producing excellent results in most cases. They can be manufactured as a gel or with macroporosity. There are also low crosslinked/high water retention styrene-based resins that are being used successfully.

Other Methods of Removing Tannins

Oxidizing agents like chlorine are effective at breaking down organic compounds like tannins. A simple jar test will show the concentration and retention time required to oxidize tannins. An activated carbon unit following the retention tank will remove the chlorine and may adsorb other organic compounds in the water. Some types of activated carbon alone may reduce the tannins to acceptable levels. Consult your carbon manufacturer for the appropriate type of product. It should be noted that the reaction between chlorine and tannins might produce trihalomethane (THMs) which are carcinogens.

Reverse osmosis is another effective method for removing tannins. Since tannins are high molecular weight organics RO should reject them effectively. However, tannins will tend to foul the membrane in the system. It also is very expensive to properly install a whole house RO system to treat all of the water.