Iron Behavior in the Ozonation and Filtration of Groundwater

Abstract

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 sand filtration. 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 mgL⁻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 mgL⁻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.

Keywords:

• Ozone
• Iron
• Filtration
• Oxidation
• Adsorption
• Groundwater Treatment
• Finland Groundwater

Notes

9. Hatva, T. “Iron and Manganese in Groundwater in Finland: Occurrence and Removal by Biofiltration,” National Board of Waters and Environment, Helsinki, Finland Publications of the Water and Environment Research Institute, n. 4, 1989.

11. IOA, “Iodometric Method for the Determination of Ozone in a Process Gas,” International Ozone Association, Quality Assurance Committee, Scottsdale, AZ, USA, Revised Standardized Procedure 001/96, 1996.

12. Kumpumäki, M. Raudan hapetusasteiden +II ja +III kvantitatiivinen määritys kiinteistä näytteistä, quantitative determination of iron oxidation number +I and +2 from solid sample. Pro gradu thesis, University of Oulu, Department of Chemistry. In Finnish with English abstract, 1998.

15. Sallanko, J. and E. Lakso, “Treatment of Humic Groundwaters, Final Report,” In Finnish with English abstract. University of Oulu, Oulu, Finland, Publications of Water Resources and Environmental Engineering Laboratory, A22. 2001.