Iron-rich drinking water residuals for phosphate and arsenic removal in waste water or surface water

“During drinking water production iron-rich residuals are formed: in the Netherlands over 75,000 tons yearly. Instead of considering this a waste material, the iron oxides can be used to remove phosphate or arsenic from water. In this project we studied the practical possibilities for this use of iron sludge.
Introduction. In the Netherlands drinking water is produced from either groundwater, surface water or river bank filtrate.
Most groundwater contains ferrous iron, which upon aeration is turned into iron (hydr)oxides. Subsequently, these compounds are precipitated, resulting in an iron- rich sludge which has to be disposed of. When surface water is used as a source for drinking water, Fe(III)-salts are added as a coagulant. The resulting complexes are precipitated, which also results in an iron-rich sludge. From literature [1, 2] it is well known that iron oxides can adsorb orthophosphate (PO43-) to form a variety of surface species. This depends on the anions’ complex- ing capacity and on electrostatic interactions with the charged (hydr)oxides surfaces. Furthermore, it is known that iron (hydr)oxides may adsorb arsenic [3, 4] in the form of arsenate (AsO43-). So, the idea was to use iron (hydr)oxides from iron sludge as a filter material for the removal of phosphate or arsenate from water.
For practical purposes granular iron(hydr)oxides would be the preferred material. Pellets are easy to handle in transport and application. However, by simply drying and grinding very instable pellets are obtained. There- fore, a suitable binder material, which does not interfere with the adsorption capacity, and palletization proce- dure had to be found first.”

(Citaat: Hofman-Caris, C.H.M., Ahmad, A., van der Kolk, O. – Iron-rich drinking water residuals for phosphate and arsenic removal in waste water or surface water – WaterSolutions (2018)4, p.26-29)