Iron removal at the drinking water treatment plant of Luleå

The study is aimed to find a suitable way to treat the iron contaminated well 21 in the Luleå water Treatment Plant in Gäddvik, Luleå. Rapid sand filtration was established to treat water pumped from the well. A pilot filter was constructed in October, 2007. The filter was run continuously and the filtrate was examined in the laboratory in different interval. The 8 months long experiment reveals the efficiency of the filter in removing iron. The period runs from the beginning of spring, winter and the starting of summer. There is a large difference in surface water temperature during this period. There are several wells in the plant contributing to the supply system. Most of them are free from iron problem. Unfortunately the well 21 is contaminated with iron and has never been contributing to the main plant due to severe iron contamination. The probable reason for this contamination is also discussed in this study depending on existing data from previous surveys. The performance of the filter in removing iron is satisfactory throughout the run. However sometimes even the pumped raw water had low concentration of iron. But even though the iron concentration is very high in raw water the filter was capable of removing 95% of it. The filter was run at different flow rates facilitating different retention times. In all cases the iron removal was quite successful. The filtrate had iron concentration lower than the standard value fixed by EPA allowable in drinking water. The plant has been suffering from turbidity problem since long time. The turbidity values from some wells are higher than the standard values (0.5 NTU). In this experiment the same problem occurred with turbidity. The filtrate water turbidity is well higher than the allowable limit. Different options like pH adjustment or aeration or the combination of both was applied to reduce turbidity although those were not quite successful. The relation of iron concentration with turbidity is also discussed in this study depending on the test results. Furthermore some recommendations have been made to solve this problem.Validerat; 20101217 (root