Iron oxidation in different types of groundwater of Western Siberia
Background, aim, and scope
The groundwaters of Western Siberia contain high concentrations of iron, manganese, silicon, ammonium, and, in several cases, hydrogen sulfide, carbonic acids, and dissolved organic substances. Generally, the groundwaters of Western Siberia can be divided into two major types: one type with a relatively low concentration of humic substances and high hardness (water of A type) and a second type with a relatively low hardness and high concentration of humic substances (water of B type). For drinking water production, the waters of A type are mostly treated in the classical way by aeration followed by sand bed filtration. The waters of B type often show problems when treated for iron removal. A part of iron practically does not form the flocs or particles suitable for filtration or sedimentation. The aim of this work was to determine the oxidizability of Fe(II), to characterize the iron colloids, and to investigate the complexation of the iron ions with humic substances and the coagulation of the iron colloids in the presence of dissolved organic matter.
Materials and methods
Water samples of the A and B types were taken from bore holes in Western Siberia (A type: in Tomsk and Tomsk region, B type: in Beliy Yar and Kargasok). Depth of sampling was about 200 m below surface. The oxidation of the groundwater samples by air oxygen and ozone was done in a bubble reactor consisting of a glass cylinder with a gas-inlet tube. To produce ozone, a compact ozone generator developed by Tomsk Polytechnic University was used. For the characterization of the colloids in the water of B type, the particle size distribution and the zeta potential were measured. To investigate the formation of complexes between iron and humic substances in the water of B type, size exclusion chromatography was used. The coagulation behavior of iron in the presence of dissolved organic substances was investigated at different pH values. The agglomerates were detected by measuring the optical density using a UV-Vis spectrometer.
Ozone showed, as expected, a faster oxidation of Fe(II) than air oxygen. The rate constants for Fe(II) oxidation were not much different for the waters of A and B types when the same oxidation process was used. However, the removal of iron after oxidation and filtration was higher in the water of A type than in the water of B type. No evidence for the formation of soluble complexes between iron and humic substances were found. In the water of A type, the coagulation process started at pH = 4.5 and accelerated with increasing pH value. In the water of B type, the coagulation of colloids occurred only at pH = 11 and higher.
The oxidation experiments indicated no major effect of dissolved organic carbon concentration on the kinetics of Fe(II) oxidation. In contrast to this, the humic substances showed a significant influence on the aggregation behavior of the iron hydroxide colloids. Due to the sorption of humic substances on the iron hydroxide colloids, they were highly stable in the pH range between 4.5 and 10. The particle size measurements confirmed the presence of small colloids in the water of B type. In contrast to this, the iron hydroxide colloids aggregated rapidly at pH = 11.
The results showed a great influence of humic substances on the iron removal from groundwaters of Western Siberia with high organic content. The sorption of humic substances on the iron colloids does not obviously allow their coagulation and formation of flocs suitable for filtration or sedimentation.
Recommendations and perspectives
By treatment of groundwaters containing high amounts of humic substances, some problems with the removal of iron are likely to occur. To increase the effectiveness of iron removal, the surface coating and pH-dependent charge effects should be taken into account by the selection and optimization of water treatment processes. The iron colloids coated by humic substances should be separated from the water phase by membrane filtration or by flocculation followed by filtration through different solid materials.
KeywordsAggregation Colloids Groundwater Humic substances Iron oxidation Iron removal Western Siberia Zeta potential
- Fomin GS (1995) Water. Control of chemical, bacterial and radiation safety according to the international standards. Encyclopaedia, Bth edn. Protector, МoscowGoogle Scholar
- Kocharyan AG (1999) Ways for perfection of the water quality normative base for water supply of the Russian Federation. In: Khublaryan MG (ed) Water problems at the border of centuries. Nauka, Moscow, p 347Google Scholar
- Serikov LV, Shiyan LN, Khasanov OL, Lukanin AA (1998) The improvement of accuracy of ozone in water determination. In: Proceedings of the 2nd Korea–Russia International Symposium on Science and Technology. Tomsk, pp 143–144Google Scholar
- Serikov LV, Shiyan LN, Tropina EA (2004) Oxidation of different forms of iron compositions in the ground water. In: Proceedings of the 8th Korea–Russia International Symposium on Science and Technology. Tomsk II, pp 82–84Google Scholar
- Serikov LV, Shiyan LN, Tropina HA (2005) Oxidation of different forms of iron compositions in ground waters. In: Proceedings of the German Russian Seminar (KarlsTom) on High-Dilute Systems: Mass Transfer, Reaction and Processes. Tomsk, pp 104–107Google Scholar
- Shubin BG, Serikov LV, Shiyan LN, Tropina EA (2002) Peculiarities of drinking water treatment from groundwater sources. Water: ecology and technology. In: Proceedings of 5th International Congress ‘AquaTech-2002’. Moscow, pp 333–334Google Scholar
- Shvartsev SL (1996) General hydrogeology. Nedra, MoscowGoogle Scholar
- State Report (2003) About the condition of water resources of the Russian Federation in 2002. NIA-Priroda, MoscowGoogle Scholar
- Tropina EA (2007) Technological system for drinking water treatment from ground waters of western Siberian region. Ph.D. Thesis, TomskGoogle Scholar
- Trufanov AI (1982) Formation of ferrous ground waters. Nauka, MoscowGoogle Scholar
- Yavorovskiy NA, Shiyan LN, Tropina EA, Pushnikova TA (2005) Peculiarities of chemical composition of ground water sources of Tomsk region. Monograph. In: Proceedings of Tomsk Scientists on the Water-Supply Systems. Tshay and K, Tomsk 648Google Scholar