High-gradient magnetic separation (HGMS) was successfully investigated for the concentration of dilute sludge wastes using a 0.3-T bench-scale system. Breakthrough curves for four different sludges containing a blend of paramagnetic metal hydroxides and oxides were measured at different feed velocities (0.0367-0.2754 cm s(-1)) and suspended insoluble solids feed concentrations (2.5-10.5 g L-1). With the aid of a dynamic model fitted to each of the breakthrough curves, the best bed utilizations of the HC MS unit and the highest enrichments of the feed were, respectively, on the order of 77% and 14 for the runs with lower feed velocities and concentrations. These results also corresponded to the HGMS unit producing on the order of 20 bed volumes of effluent free of suspended insoluble solids prior to breakthrough. Overall, the performance of the HGMS unit for this type of process was considered to be quite good, given the broad range of particle sizes, magnetic susceptibilities, and molecular species in each sludge waste. These results suggest that HGMS can be used as an effective and alternative treatment method for the concentration of a variety of dilute waste streams containing suspended solids of a diverse nature.