Illinois River Dredged Sediment and Biosolids Used as Greenhouse Soil Mixtures

Accumulation of sediment in the Illinois River has greatly degraded the ecosystem. A large dredging project has been proposed to improve wildlife habitat and recreation in the Peoria Lakes reach of the river. Disposal of the dredged sediment is a concern because of the large quantities involved. The objective of this study was to determine if mixtures of dredged sediment with other materials, including biosolids, yard waste compost, and horse manure could serve as topsoil substitutes. Dredged sediment came from the Peoria Lakes portion of Illinois River, compost was obtained from the Urbana, Illinois municipal yard waste facility, and biosolids were obtained from the Metropolitan Water Reclamation District of Greater Chicago. Eighteen different mixtures were produced. Barley and snapbeans were grown in the mixtures in the greenhouse. Plant growth, total biomass, and heavy metals content were analyzed as well as physical and chemical properties of the soil mixtures. The experiment was carried out twice using the same soil material. Plants grew well in all treatments, except snapbeans were stunted by salts in unleached biosolid mixtures. The highest overall yield for barley was obtained in the treatment composed of 50% sediment and 50% biosolid. For snapbean, the highest yield was the treatment composed of 70% sediment and 30% biosolid. Heavy metals in plants tissue are within ranges considered normal, except for Mo in snapbean which is at a level of concern if the plants were used exclusively as animal fodder. Addition of biosolids to sediments decreased Mo plant availability. Compost did not have a significant effect on yield, but did significantly increase Mo uptake in snapbeans. Based on our results with this limited greenhouse experiment, the dredged sediment we used has no inherent chemical or physical properties that would preclude use as topsoil substitute. Adding dredged sediment to unleached biosolids improved plant growth and an optimum ratio of sediments to biosolids might be 80:20 to 70:30 in most situations.