Tannins in Water – how they form.
Tannins are commonly formed in borehole water, due to humic acid. Humic acid is a major component of humic substances, also known as NOM – Natural Organic Matter (The dark brown constituents of soil). Also found in coal, peat, seawater, and many upland streams, tannins are bitter, astringent, plant polyphenols that bind and precipitate proteins.
The word “tannin” refers to the source of tannins that are used when tanning animal hides into leather. However, “tannin” is also a comon term in the water treatment industry, meaning brown color in water, which is caused by rotting organic substances.
color in the water is from tannins or humic acids, then the self-cleaning, automatic tannin water filter, might be the suitable choice. These tannin filters remove dissolved color by way of ion-exchange, using anion exchange filter media. These filters regenerate with sodium chloride (rock salt).
Although these water filtration units are generally called tannin filters, they are in fact, ion-exchange units. Often we notice boreholes or wells that are under the influence of surface run-off water, result in high levels of tannin, during heavy rainfalls.
Tannin filters are a relatively low-cost and effective technology to use for this type of problem, especially if the nature of the problem (like sealing off the borehole) cannot be successfully achieved.
In some borehole water, in addition to tannins, there will be iron or manganese. Water that has high levels of iron or manganese is sometimes rust colored, red, brown, black, tan or green. Ozone disinfection or water chlorination, following by a custom designed iron filter, is a very effective way to remove tannins and these oxidized iron particles.
Generally, the first step to treating water that contains colloidal particles and/or water that has tannins, is to inject a coagulant aid, or to inject a floculant, which will allow these microscopic, suspended particles to lose their positive charge and “floc” together into larger clumps.
This water treatment process is easily achieved with smaller scale systems, by installing a metering pump, and injecting 2-5ppm of “Cat-Floc” (One of the many floculant aids used for this type of water problem) into the water, as it flows into a holding tank, or storage tank.
The water is then allowed to settle, and then followed by water filtration to remove any suspended “floc”. Sometimes, to get the floc to form, the water may need to be slighlty agitated or gently stirred.
An extremely effective way to remove tannin from water is by using Advanced Reverse Osmosis, or Ultra Filtration membrane systems. RO and UF systems to remove high levels of turbidity in water are ideally suited for home-owners, commercial sites and small communities, to produce pure, crystal clear water with less than 0.1 NTUs
Direct filtration is also an option, depending on the nature of the tannin. A backwashing sediment filter, using a special type of Zeolite filter media, is an excellent way to clarify your water. Direct Water Filtration can remove sediment down to the 5 to 10 micron range, where it is then periodically backwashed out by the automatic control valve.
The whole house cartridge water filter are large size filter cartridge systems, which come in a range of micron ratings, right down to 1 micron size. A common option used by home-owners with tannins in their water, is the 1 or 5 micron filter cartridge system.
When removing tannins in water, there are many different designs and application criteria to be considered, including the water chemistry, flow rates, how the water will be disinfected, and what types of water filtration to use.
In certain cases, additional water treatment methods, such as reverse osmosis or other membrane filtration systems are used in conjunction with the polymer injection and settling to remove tannins.
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