Color in Water

There are many factors that may cause color in water. The most common are organic matter, and/or colloidal solids that are too small and too fine to settle out properly. These suspended particles can cause problems with disinfection processes, and also be an indicator of bacterial activity in the water. Turbidity is measured in NTU's, (nephelometric turbidity units). The turbidity of drinking water should always be less than 1 NTU. Most treated city water is less than .2 NTU.

If the color is from tannins or humic acids, then a tannin filter might be applicable. These filters remove dissolved color by ion-exchange, using anion exchange media. The units we use regenerate with rock salt (sodium chloride). While these are called tannin filters, they are really ion-exchange units. Frequently we see shallow wells, or wells under the influence of surface run-off water, achieve high levels of tannins during heavy rainy periods. Tannin filters are often an excellent relatively low-cost technology to use for this type of problem, if the actual cause of the problem (such as sealing off the well from the surface) cannot be achieved.

While it is possible to filter water containing colloidal particles, and/or water that has a color to it, generally filtration is the last step in a process of treating this type of water. Since we primarily supply treatment equipment for very small systems, the type of treatment we might recommend is different than what large-scale municipalites use to treat turbidity.

One method we have used successfully for color removal involves injecting a flocculant, or coagulant aid, which allows the microscopic suspended particles that create the color in water, to lose their positive charge and "floc" together into larger clumps. This is easily done on small scale systems by using a metering pump and injecting 2 -5 ppm of "Cat-Floc" (one of many types of flocculant aids used for this purpose) into the water as it flows into a holding tank or storage tank. The water is allowed to settle, and is then followed by filtration to remove any suspended floc.

There are many different designs and application criteria that must be considered, including water chemistry, flow rates, how the water will be disinfected, and what types of filtration to use. In some cases additional treatment such as reverse osmosis or other types of membrane filtration, such as nano-filtration are used in place of or in conjunction with polymer injection and settling, for color removal.

The best first step in determining what types of processes to use in removing color is to get an accurate water analysis. You can also fill out an online technical request form and one of our water technicians will assist you in trying to identify the cause of the problem and recommend a solution.