The production of drinking water generates iron sludge as a residual. The iron sludge contains ferric (hydr)oxides, which are able to adsorb substances such as arsenic and phosphorus. This project researched how the iron sludge – via pelletisation – can acquire a solid form [granular ferric (hydr)oxide]. In addition, the iron pellets have been tested in the removal of the above-mentioned substances from water.
The objective of this project was to establish the potential of granular ferric (hydr)oxide, or granular aquafer, which is made from the ferric (hydr)oxide residual, for the adsorption of arsenic and phosphorus. The research examined how granular aquafer can be produced on a large scale and sustainably, and how to ensure that the material has the consistent chemical and physical quality required of an adsorbent in water (courses). During a period of over six months the material has been tested on a pilot scale for the removal of phosphorus from surface water and arsenic from drinking water at three different locations.
First the current status of the technique and the regulatory framework has been established. Drinking water production sites with iron-rich sludge – from various sources, and of varying composition and age – have been selected for the production of granular ferric (hydr)oxide. The materials were tested on a laboratory and pilot scale. The lab research determined various materials that are suitable for arsenic and phosphorus removal. These iron pellets have been produced from (mixtures of) selected wet sludges on the basis of prevailing and practicable methods, such as drying and pelletisation. The removal of phosphorus from surface water by the granular aquifer was then studied at Waternet, on a pilot scale under representative conditions. Arsenic removal was the object of study at Brabant Water, from deep groundwater, and at Dunea, from dune filtrate. In all cases effective removal of either phosphate or arsenic was observed during the whole testing period of over six months.
The project has provided an efficient adsorbate (of constant composition and quality) for the removal of phosphorus and arsenic from water. The adsorbate is produced from the iron sludge residual generated in the drinking water production process.