The company Sydvatten supplies drinking water to 900,000 people in western Skåne. The water comes primarily from Lake Bolmen and runs through an 80-kilometer-long tunnel to the Ringsjö Water Treatment Plant, where raw water is converted into drinking water. In the purification process, iron chloride is used to create a chemical precipitation that removes microorganisms, solid particles and unwanted substances from the raw water. The sludge that remains contains organic substances bound to iron compounds. The sludge in itself is harmless and could for example be used to bind phosphorus in agricultural soil, but there is currently no lucrative way to recover the iron chloride, something which could entail economic profit while also benefitting the environment.
“The volumes are large,” explains Kenneth M. Persson. The Sydvatten Water Treatment Plant produces about 70 million cubic meters of drinking water each year and uses several thousand tons of iron chloride.
“We would like to recover and recycle the iron chloride, but the bond between the organic matter in the sludge and the iron compounds which are formed are very complex and difficult to study. That’s why we turned to the MAX IV Laboratory, through the Science Link project, hoping to get a clearer picture of the structure of the sludge.”
With the help of staff at the MAX IV Laboratory, EXAFS was identified as a suitable technique for analyzing Sydvatten’s sludge samples. The experiments which were carried out revealed for the first time a three-dimensional image of the structure of the sludge and its composition at the atomic level.
“You could say that the MAX IV Laboratory gave us access to microscopy at a level of detail that we haven’t even been close to before. The experiments and the help we received in interpreting the results gave us a stunningly detailed analysis which now forms the basis of a project to find methods for effectively separating the iron from the organic substances. It is very likely that we will continue to make use of the resources at the MAX IV Laboratory to move forward in the process. Our vision is to be able to recycle and re-use the iron chloride in water purification and at the same time produce a completely harmless organic sludge which can be used for example in soil improvement.
To find out how substances are structured at the nanometer level requires extremely sensitive methods. One such method is EXAFS, or “Extended X-ray absorption fine structure”, which is used to examine the structure of materials at the atomic level. The method involves scanning the photon energy of an X-ray beam across a so-called absorption edge, i.e. the energy where the inner electrons in the atoms of a specific element start to absorb photons and are released from the atom. The appearance of the absorption provides information on which other kinds of atoms exist around it and the distance to them.