Tannins are organic matter, sometimes found in water that give a light yellow to a dark tea colour. This effect is caused by a variety of humic and fulvic organic acids, which are typically found in waters influenced by rainfall on hillsides, running off through natural soild and peats into streams, rivers and lakes. Tannins have also been found in deep groundwater wells.

The Purolite^® resins of choice for this application are:

A500P
A850
A860
A870
Tanex

Since there is such a wide variety of Tannins known to exist, and since each type will respond to a particular resin, it is recommended that a bench test be performed to determine resin choice.

The complexity of any Tannin form is such that it is difficult to identify each by water analysis. Typical water analyses will provide an indication of Tannin level in ppm. Each Tannin removing resin has a capacity reported as total ppm. Dividing the total ppm capacity by the ppm level in the particular water will offer a good estimated capacity.

These Purolite anionic type resins are regenerated with brine, using the Chloride portion of the salt.

It is possible to top dress a Purolite cation resin bed with the appropriate Tannin removing Purolite resin to perform water softening and tannin removal within the mixed bed. It is highly recommended that a minimum 15cm or 6" Purolite Tannin removing resin bed be top dressed on the cation bed. This can be done when the water Hardness is less than 170 mg/l or 10 gpg. Since the Purolite Tannin removing anion resin is lighter in specific gravity, adjustment must be made to the backwash flow rate for the mixed bed. It should be reduced by 30 - 50% and the backwash time doubled. In addition, an upper strainer basket should be installed on the inlet of the vessel to prevent resin loss during backwash.

Purolite Tannin removing resins can also be used in a separate vessel when water quantity requirements demand. The same adjustments to the vessel and controls as for a top dressed system must be made.

When the water Hardness exceeds 170 mg/l or 10 gpg it should be softened.