Vattenrening genom komplexbildning mellan järn och humusämnen : en litteraturstudie med försök

Sammanfattning: The aim of this work was to study if two natural waters could be purified from iron and organic substances without the addition of chemicals. The working hypothesis was that complexation reactions between iron- and humic substances would happen spontaneously when two waters were mixed and that this reaction could be used for purification of surface- and groundwaters into water of drinking quality. The complexation reactions were studied through literature and experiments to determine if optimisation of the conditions could promote the creation of complexes between the two substances. The tests were carried out at the water plant in Älmhult, by mixing an iron rich ground water with a surface water, rich in humic-substances. The setup of the test consisted of a gravel filter, a mixing jar and a sand filter. The concentration of iron and organics were determined at different points in the test setup. The results showed that after mixing, the iron and humic concentrations were the same as the theoretically calculated values, e.g. iron was not accumulated in the gravel filter. After the sand filter, the concentration of the iron was reduced by 80 %, while the humic concentration was almost unchanged. The main reason why iron and humic substances did not complexate is probably due to complete oxidisation of the iron into Fe(OH)3 which precipitated into the solution and thereby did not participate in the adsorption of humic substances. It is also possible that other reactions, that were out of this test’s control may have influenced the results. At the same time a high degree of dissociation may have caused the humic substances to stay dissolved in the solution or as colloids. To optimise the conditions for complexation between iron and humic substances it is recommended that the mixing time is extended. This could be done, for example, by using a flocculation chamber and adjusting the pH.