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Impact of iron on UV disinfection

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Posted on August 14, 2018

If you have iron in your water, you’ll know it. Not necessarily because you see it in the water, but because you see the stains it can leave on bathroom fixtures - and even on your clothes! And worse than that, iron in your water can prevent your water from receiving optimal disinfection.

Iron in groundwater is a very common problem for well owners, second only to the presence of hardness shutterstock_101858818minerals. According to a study published by the United States Geological Society (USGS), iron was detected in about 45% of domestic wells. Although iron in water is not considered a health concern, there is a certain level where the poor taste of the water and staining will become more challenging. Nearly one in five (19%) of US wells tested showed the iron level exceeded the non-health guideline. Higher levels of iron were more common in the eastern half of the United States, but it was found everywhere.

 

Iron, as it turns out, exists in different forms. The iron in groundwater is ferrous iron (Fe 2+). It’s dissolved in the water and so it can’t be seen. But when the water comes out of the tap, the water is exposed to air and the iron is oxidized to ferric iron (Fe 3+). Ferric iron is not soluble in water, and and it will show up as rusty-brown deposits on everything from your bathroom and kitchen fixtures, to your washing machine, and even your clothes.
So, how do you get the iron out of the water before the damage is done?


Oddly enough, for high levels of iron, oxidation can be part of the answer. But the oxidation has to happen before the water leaves your tap. Some common oxidizing agents are chlorine, ozone, hydrogen peroxide, and oxygen itself. Adding any one of these to your water will cause ferric iron compounds to form as tiny solids, which can then be removed by filtration. This two-step process can be used for any levels of iron in water.
If you don’t want to add chemicals to your water, the dissolved iron can be removed in one step using synthetic zeolite-based cation exchange media in a whole-home system like this one. This is a great solution if you have high levels of iron plus hardness minerals in your water. If there are only low levels of iron in your hard water, then a water softener is likely all you need.


If you’re planning to use ultraviolet (UV) disinfection, it’s important to reduce iron levels to below 0.3 ppm (parts per million). Otherwise, the iron will interfere with the ultraviolet transmittance (UVT), and will also cause sleeve fouling. Both the UVT and fouled sleeve interfere with UV dose, which impacts the level of disinfection your water is receiving. Remember, you’re investing in a UV system to deal with any harmful microbes like E. coli, Giardia, or Cryptosporidium, that might end up in your water supply. So don’t let iron keep your UV system from doing its job!


The impact of iron in your water can be more serious than just ugly stains. Be sure to get your water tested and talk to a water treatment professional to help identify the best solution for your needs.