2008:058 MASTER'S THESIS Iron Removal at the Drinking Water Treatment Plant of Luleå Ahmed Fahim Faisal Luleå University of Technology Master Thesis, Continuation Courses Environmental Engineering Department of Civil and Environmental Engineering Division of Sanitary Engineering 2008:058 - ISSN: 1653-0187 - ISRN: LTU-PB-EX--08/058--SE PREFACE This work was carried out from October 2007 to June 2008. The work is targeted to find out a suitable solution to activate the drinking water well 21, at the drinking water plant in Luleå which is severely contaminated by iron. The well had never been connected to the main distribution plant due to this serious contamination by iron. There are a number of investigations to add the well in distribution system, mentioned in the report. Unfortunately those were not successful. Hence the recent study is performed to find a suitable way to get rid of iron from drinking water. In this regard several samples have been collected in different times and analyzed in the laboratory. The results are analyzed and discussed in this report. The 8 months study is mandatory to achieve Masters Degree. The work was arranged by Luleå University of Technology and Technical office of Luleå Kommun. The work was performed at the Water Treatment Plant in Luleå. Several travels have been made to the plant to examine the samples collected of different times. I place special thanks to my supervisor Professor Jörgen Hanaeus, Division of Sanitary Engineering for his continuous guidance and instruction for the work. I am undoubtedly grateful to him for solving my thousands of doubts. I am also thankful to all the operators at the plant Lars-Olof Eriksson, Börje Lantto and Patrik Fahlen for their time-to-time help and all necessary background information I need for composing the report. I specially thank Patrik Fahlen for his willful support in establishing the pilot filter and providing all the necessary information about the well as well as the water quality without which the work is incomplete. On this occasion I would also like to thank my wife Ashfia for her encouragement and support to perform the work. ii ABSTRACT 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 the 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 value (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. iii Table of content 1 INTRODUCTION ……………………………………………………………..………1 2 BACKGROUND ....…………………………………………………………………….2 2.1 Iron chemistry…………......……………………...…………………………………2 2.1.1 Iron in water…………......……………………...……………………………...2 2.1.2 Source of iron in water…………......……………………..…………………....3 2.1.3 Effect of iron in water…………......……………………..…………………….4 2.1.4 Standard for iron in drinking water…………......……………………...………5 2.2 Description of the plant…………………………………………..............………….5 2.2.1 Treatment method ………………………………………………………….…7 2.2.2 Process ………………………………………………………………………..7 3 WATER TREATMENT TECHNIQUE ……………………………………………...8 3.1 Unit processes ……………………….………....……………………………...........8 4 IRON REMOVAL BY FILTRATION ..............…...........................………………..10 4.1 Filter medium…………………………...…………………….....…………………10 4.2 Properties of filter media……………….………………………………………….10 4.3 Rapid sand filtration ………………….……..………………………………..……11 4.3.1 Filter media……………….…………………………………………………..12 4.3.2 Head loss development………….……………………………………………12 4.3.3 Flow control during filtration…………..……………………………………..12 4.3.4 Backwashing……………………...…………………………………………..12 5 OBJECTIVES ………………………………………………………...……...…….....13 6 MATERIAL AND METHOD ……………..…………………………………………13 6.1 Pilot filter……………………..………………………………….......…………….14 6.2 Setting up the pilot filter ……...…………………….............……………………..14 6.3 Sampling the pilot filter….………………………………………………………...16 6.4 Laboratory equipment….…………………………………………………………..16 6.5 Laboratory analysis…………………...……………………………………………16 6.6 Laboratory experiments……………………………………………………………18 7 RESULTS ………………………………………………………………………..…....18 7.1 The pilot filter……………...…………………………………….......…………….18 7.1.1 Determination of the parameters……………………………………………..19 7.1.2 Determination of pressure drops……………………………………………..23 7.2 Results of the laboratory experiments……………….............……………………..23 8 DISCUSSION …………………………………………………………………………26 8.1 Iron removal……………………….…………………………….......…………….26 iv 8.2 Turbidity reduction ……………..………………….............………..…………..27 8.3 Optional experiments……………………….………….………………………...28 8.4 Summary discussion…………………………………….………………………..29 9 CONCLUSIONS.. ………………………..……………….…………………………30 9.1 Findings……………………………………………….……….......…………….30 9.2 Suggestions for future work…..…………………….……………...…………….31 10 List of references ……………………………………………………………………31 Appendices Appendix I Treatment plant layout……………………….……………………………..33 A) Treatment process….……………………….……………………………..33 B) Location of the wells………….…………….……………………………..33 Appendix II Previous investigation in well 21, 2000……………..……………………..34 Appendix III WHO guideline for aesthetic quality……….……………………………..34 Appendix IV River water quality parameters…………….……………………………...35 Appendix V Size distribution of particles in water and of filter materials………….…...36 Appendix VI Equipment for laboratory analysis…………….…………………………..36 A) Thermometer……………………………….………………………………36 B) pH meter…….…………….………………………………………..………37 C) HACH 2100 Turbidity meter……………….……………………………...37 D) Color kit……………………….…………….……………………………..38 E) Colorimeter……..….……………………….……………………………...38 F) Yellow Springs 58 Oxygen meter………….………………………………39 Appendix VII Method of iron detection by colorimeter.….……………………………..40 Appendix VIII Test results. ……………………………….……………………………..41 A) Results for different parameters at pilot filter runs….……………………..41 B) Results if pressure drops…...….…………….……………………………..43 v Tables and Figures Tables 1 Pressure drop for different flow rates in different time duration ………………23 2 Turbidity and iron content after stepwise addition of acid to raw water from well 21 and filtration……………………….24 3 Turbidity and iron content after addition of alkali and filtration ………………25 4 Turbidity and iron content after aeration of different duration followed by filtration .. ………………………..………….26 Figures 1 Location of the drinking water plant in Luleå ……..…………………..………….1 2 pE-pH diagram of iron system ………………………..………………..………….4 3 Water treatment processes in Luleå water treatment plant .……………………….6 4 Process of rapid sand filtration ………………………………………..…………11 5 The pilot filter…………………………..………………………………………...15 6 Temperature recording of water samples from the pilot filter ………..………….19 7 pH values of water samples from the pilot filter ………………...……………….20 8 Turbidity of water samples from the pilot filter ….…….……………..………….20 9 Color of water samples from the pilot filter …………...……………...………….21 10 Iron content of water samples from the pilot filter…..………………..………….22 11 Oxygen content of water samples from the pilot filter ……………..……………22 12 Co-relation between turbidity and iron content in treated samples from well 21..27 vi 1. INTRODUCTION Water is considered as another name of life. About 66% of the human body is considered to be water. It is the main transporter of all nutrient and air to cells. If there is shortage of water occurs dehydration follows. On the other hand drinking of polluted water will cause different diseases like diarrhea or cholera. Hence pure drinking water is a fundamental right of all on the earth. Only 3% of the water in the world is fresh. About 2/3 rd of this is frozen in polar ice caps and glaciers. Major portion of the rest is ground water and only 0.3% appears as surface water. About 7/8 th of this fresh surface water is contained by freshwater