In the Netherlands drinking water treatment practically always generates aquafer as a residual. By treating this material with acid, we intend to reproduce iron salts. The salts can then be reused as a flocculant in drinking water or wastewater treatment.
Reuse of iron salts
The abstraction and treatment of drinking water always involves the formation of aquafer (iron sludge), either through the aeration of ferrous groundwater, or through the addition of iron salts as a flocculant. By treating this iron sludge with acid, iron salts can again be made and then reused as a flocculant in wastewater or drinking water treatment processes. The material can therefore be reused and the resource loop closed.
Research into technical and economic feasibility
Attempts have been made in the recent past to reuse iron salts in this manner. We started by examining where to expect possible problems in the process. We then conducted lab experiments to establish the composition of the aquafer from the different sites, and the best way of extracting the iron. This was followed by research on how the extracted iron functions as a flocculant compared to commercial flocculants, and how possible foaming problems might be prevented. The results showed that the iron extraction performance depended on the sludge type, but that, in specific cases, an efficient extraction is indeed possible, and that the extract in coagulation experiments achieved the same results as commercial iron salts. Furthermore, the costs involved are lower. We are now preparing a pilot research project. To start with, the extracted iron will be applied as a flocculant in a wastewater treatment process, since application in drinking water processes requires certification.
Circular process promotes sustainability
The use of flocculants accounts for a large part of the footprint of drinking water treatment. Moreover the drinking water utilities are in search of application possibilities for the formed sludge. Exploratory LCA studies have shown that making flocculants from aquafer and the reuse of these flocculants can significantly shrink this footprint. This study will examine whether this can be realised in practice.