Polishing pellets

The production of drinking water results in sludge with a high level of iron oxide/iron hydroxide. That sludge can be used as an adsorbent for, among other things, phosphate and arsenic. The drawback is that the sludge is released in a way that limits the practical application options, as well as transport and handling. In this project, we are trying to solve this problem by making pellets from the iron oxide/iron hydroxide.


The adsorption of phosphate and arsenic takes place on the surface of the iron oxide/iron hydroxide. This means that as much surface area as possible is required for an effective adsorbent. Meaning that pelletisation methods based on pressure are not appropriate. In this project, we are looking for an approach that will produce porous but stable pellets. A rotating disk pelletiser could be suitable for this purpose. In addition, a binder will have to be found that meets several requirements. The binder must enhance the mechanical stability of the pellets without reducing adsorption capacity. It will also have to be possible to use it in, for example, surface water and drinking water.


The drawback of aquafer – sludge with a high level of iron oxide/iron hydroxide – is that the material is released in the form of a slurry (approx. 8% solids content) or as a ‘dewatered’ material (approx. 30% solids content). That makes transport and handling difficult. A brief desk study will be carried out as the first step, looking at potentially applicable pelletisation techniques and binders. That will be followed by field tests with the most promising technique in combination with a number of binders. The focus here will be on both the effect on strength and the adsorption capacity of the pellets. In addition, tests will be conducted to see whether a washing procedure is needed to wash out unwanted materials and, if so, to identify the optimal approach.


If the production of aquafer in the form of stable pellets is successful, it will open the way to higher-grade applications for sludge from drinking water treatment. The benefit for drinking water companies is that the pellets will make their residual flow more versatile and increase its value. With this innovation, the companies can, for example, remove arsenic from drinking water themselves. In addition, water authorities may be interested in using the pellets for phosphate removal from surface water.