Iron behavior in the ozonation and filtration of groundwater

In Finnish groundwater, the main substances that require treatment are iron and manganese. In addition to this, groundwaters are soft and acidic. Iron removal is usually relatively effective by oxidizing dissolved iron into an insoluble form, either by aeration or chemical oxidization and removing the formed precipitate by sandfiltration. Sometimes, if the untreated water contains high amounts of organic matter, problems may arise for iron removal. In Finland, it is quite common that groundwater contains high levels of both iron and natural organic matter, mainly as humic substances. The groundwater of the Kukkala intake plant in Liminka has been found to be problematic, due to its high level of natural organic matter. This research studied the removal of iron from this water by means of oxidation with ozone and filtration. While the oxidation of iron by ozone was rapid, the precipitate particles formed were small, and thus could not be removed by sand and anthracite filtration, and the iron residue in the treated water was more than 2 mg L-1. And while the filtration was able to remove iron well without the feed of ozone, the iron residue in the treated water was only 0.30 mg L-1. In this case, iron was led to the filter in a bivalent dissolved form. So, the result of iron removal was the best when the sand/anthracite filter functioned largely as an adsorption filter.