Screening of valorisation opportunities for iron sludge from drinking water J. Bergmans 1 , K. Broos 2 , G. Peleman 3 , S. Vandenbroucke 4 , V. Van Hoof 5 , P. Nielsen 6 1) VITO, jef.bergmans@vito.be 2) VITO, kris.broos@vito.be 3) De Watergroep, gisele.peleman@dewatergroep.be 4) De Watergroep, serge.vandenbroucke@dewatergroep.be 5) VITO, veronique.vanhoof@vito.be 6) VITO, peter.nielsen@vito.be Abstract: During the production of drinking water, an inorganic sludge rich in iron hydroxides (iron sludge) is produced. Although this sludge is typically low in contaminants, its disposal forms a significant cost for drinking water companies. The valorisation of 2 types of iron sludge was investigated: a type originating from groundwater extraction and a type from the treatment of surface water. Based on the physical and chemical characteristics of these 2 types, we present an overview of potential applications for which iron sludge can qualify. This overview exists of both known applications and new research ideas. Next to low-grade applications (e.g. in the building industry), several more high-grade applications are also described that take into account the main strengths of iron sludge, a fine-grained material with high iron content and a strong adsorption capacity. The proposed applications are evaluated on 5 criteria: societal & environmental implications, technological feasibility, quality requirements, economics and market size. Keywords: Iron sludge; Recovery; Potential applications Introduction Iron sludge is produced in the production of drinking water, both during the extraction of groundwater and the treatment of surface water. When groundwater is extracted, the water will be subjected to an aeration step, followed by sand filtration. The elements that are present in the water (e.g. Fe, Mn) will oxidize and precipitate. The precipitated sludge, rich in iron, can adsorb other elements (e.g. As). Surface water needs to be cleared from poorly sedimentable substances, colloids and part of the solutes. This is done by the addition of a flocculant, mostly FeCl 3 . The resulting flocs will settle and form a sludge (i.e. iron sludge). Iron sludge mainly contains amorphous iron hydroxides (Koopmans et al., 2010). Iron hydroxides show a strong adsorption of P and As (Pierce & Moore, 1982) (Chardon et al., 2012), but also adsorption applications for other elements (e.g. Cr) are reported (Mustafa et al., 2009). In Flanders, iron sludge is currently disposed in three applications: biogas facilities (reaction with H 2 S), agriculture (soil enhancer) and cement production (personal communication De Watergroep). Next to the use in biogas facilities, iron sludge in The Netherlands is also used in sewage treatment plants, brick production and low-grade building applications (embankment) (Personal communication De Reststoffenunie). The disposal to these applications, however, still forms a significant cost. In this study, we will screen several valorisation opportunities for iron sludge that can create an added-value. The investigated applications (stabilisation of contaminated waste streams, biogas installations, pigment in concrete, iron reactive barriers, sewage treatment, brick production, low-grade building applications, production of FeCl 3 , cement industry, agriculture) are screened and evaluated on 5 aspects: societal & environmental implications, technological feasibility, quality requirements, economics and market size.