Experimental Study on the Valorization of Dredged Sediment from Reservoirs in Tunisia as Soil Amendment Regulating Metal Uptake by Crops

Abstract

Abstract-Sediment deposited on the bottom of water reservoirs is known as clayey waste which causes a big problem in the sense of sustainability of surface water resources in Tunisia. Every year, the water storage capacities of reservoirs are decreased by more than 1%. To cope with this situation, Tunisian government has adopted a national strategy for water and soil conservation since 1956. Nevertheless, the sedimentation rate is still high because this strategy is limited on the implementation of soil conservation measures such as terraces and hill lakes in some watersheds. Dredging, conventional but most effective countermeasure against sedimentation, is now required to recover the storage capacity of reservoirs. However, such countermeasure is not carried out in Tunisia because of its high cost. We have previously suggested to commercially valorize the sediment in order to cover partially the financial burden of the dredging activity. In this paper, we studied on the potential of the use of sediment as soil amendment. Sediment samples were extracted from different reservoirs in order to evaluate their ability to adsorb heavy metals and regulate the metals uptake by crops. Two methods have been carried out: a batch adsorption study and a semi field test. Results of this study show that the adsorption capacity is dependent on the mineralogical composition and the organic matter content of sediments. Metals are adsorbed on clay particles and carbonates containing in sediments, which decrease its mobility and accumulation in plants. The possibility of sediment valorization as soil amendment or adsorbent material is confirmed.