干旱区生态环境知识资源中心

The Cebala area faces serious problems of salinization caused by shallow saline groundwater and bad drainage system. Situated in northern Tunisia, it is considered the largest area irrigated with treated wastewater in Tunisia. To analyze the environmental impact of the reuse of treated wastewater, an experimental plot was installed in a secondary open drainage for more than 2 years. In this paper, we present the main experimental results: an analysis of volume and the salinity of drained water, a characterization of chemical parameters and heavy metals in drainage water and the exported quantity of salts and heavy metals. From July 2013 to January 2016, we measured in 36 ha, a total sum of 985 m(3) ha(-1) d(-1) drained water with an average flow of 1.07 m(3) ha(-1) d(-1) and an average total dissolved solids (TDS) of 6 g L-1. The characterization of the drainage water shows a neutral to slightly alkaline pH of water. The chemical compositions of soluble salts show that the drainage water is dominated by the sodium and the chloride. The heavy metals Zn, Ni, Fe and Cr were the most abundant elements in the drainage ditch, whereas Cu and Cd were the less abundant ones. Compared with the Tunisian standard for the discharge of treated wastewater NT 106.02, both Cr and Cd concentrations constantly exceed it. This paper shows that special attention needs to be given to the drainage system in Cebala. This is due to the accumulation of 214 tons of slat in 36 million m 3 drainage water through the drainage ditch D2. The exported mass of heavy metal in the sampling site was in decreasing order of: Cr > Zn > Ni > Co > Pb > Mn > Cd > Fe > Cu. However, further studies are needed to assess their long-term potential risk on the environment.