Contaminated (in)organic sludges, coming from river b d sediments or from industrial production processes, are causing w orld ide a large threat for humans and ecology. This is not only related to toxic comp unds, but also to the large amounts of sludges that are disposed in landfills. Ex situ techniques are commonly practiced to obtain a better dewatering and consolidation of the sludges as pretreatment for disposal in new landfills. Reduction of the water concentrat ion in the sludge would increase the geostability, decrease the leaching of toxic compou nds and reduce the sludge volume in the landfill. This leads to an increased disposal c apa ity, which is of high economic importance, especially for dredging sludge and mine tailings. In the ‘In situ sludge consolidation’ project, techniques will be studied and developed for the in situ consolidation and stabilization of inorganic sludg es, both in landfills as directly in contaminated sediments. The ‘ In situ sludge consolidation’ project is executed by a consortium which consists of 4 resear ch centers (Flemish Institute for Technological Research, Catholic University of Leuv n, University of Ghent and the Catholic University College of Ostend-Bruges), eigh t companies (MWH, ENVISAN, Rasenberg Milieu, DEME Environmental Contractors, G hent Dredging, WVRB, Nyrstar and Tessenderlo Chemie) and two public orga nizations (Port of Antwerp and the Agency for Maritime and Coastal Services). This paper describes the objectives and specific research goals of the ‘ In situ sludge consolidation’ project. INTRODUCTION Contaminated inorganic sludges are causing worldwid e a large threat for humans and ecology. This is not only related to their ofte n high contents of toxic compounds (heavy metals and organic pollutants), but also due to the huge amounts of sludges that need to be processed or disposed in landfills. Inor ganic sludges originate from dredged river bed or harbour sediments and are also produce d in several industrial processes (ferro, non-ferro, chemical and mining industry). Inorganic sludges are often disposed in landfills a nd re generally characterized by high water contents and low geostability. These lan dfills are not always safe because of risks for leaching of the contaminants to the groun dwater and every year several dam breakages result in large environmental disasters. Several ex situ techniques have been developed and are commonly practiced to obtain a be tter dewatering and consolidation of the sludges as pretreatment for disposal in newl y created landfills. However, for existing landfills, in situ techniques for improved consolidation and dewaterin g of the sludge would be needed and very beneficial. In situ dewatering and consolidation of sludge in existing landfills would increase the geostability, decrease the leaching of toxic co mp unds and reduce the sludge volume in the landfill. This leads to an increased disposal capacity, which is of high economic importance since finding new locations for landfills becomes more and more problematic. Worldwide, sediments in rivers and est uaries are also often highly contaminated with heavy metals and organic pollutan ts, which may represent a serious environmental and ecological risk. When these sedim nts do not need to be dredged for nautical purposes, there also arises a need for in situ sanitation techniques in order to reduce the risks of these contaminated sediments. This paper describes the objectives and specific re search goals of the ‘ In situ sludge consolidation’ project which is executed in Flander s (Belgium) in the framework of the Environmental Technology Platform (MIP) since October 2007. THE ‘ IN SITU SLUDGE CONSOLIDATION’ PROJECT The ‘In situ sludge consolidation’ project is executed by a con sortium which consists of 4 research centers (the Flemish Institu te for Technological Research (VITO), Catholic University of Leuven (KUL), University of Ghent (UGent) and the Catholic University College of Ostend-Bruges(KHBO)), eight c ompanies (MWH, ENVISAN, Rasenberg Milieu, DEME Environmental Contractors, G hent Dredging, WVRB, Nyrstar and Tessenderlo Chemie) and two public orga nizations (Port of Antwerp and the Agency for Maritime and Coastal Services). In the ‘In situ sludge consolidation’ project, techniques will be studied and developed for the in situ consolidation and stabilization of inorganic sludg es, both in landfills as directly in contaminated sediments. Th e in situ approach is based on injection of additives into the sludge in order to obtain improved dewatering and consolidation of the sludge and in order to immobil ize the pollutants present in the sludge. A schematic overview of the approach for in situ sludge consolidation in a pond is shown in Figure 1. FIGURE 1. Schematic overview of the approach for in situ sludge consolidation and stabilisation in a pond: (A) additives are injected into the pond for sludge dewatering and stabilization of the pollutants; (B) Removal of wat er after improved dewatering creates extra available volume, stabilization of pollutants reduces the risk of leaching to the groundwater; (C) extra volume can be used for addit onal sludge deposition; (D) improved geotechnical stability enables construction of buil dings or a dike on top of the existing pond, creating additional volume for sludge deposi tion. GW A