Analysis and speciation of heavy metals in the water, sediments, and drinking water plant sludge of a deep and sulfate-rich Algerian reservoir.

This research work aimed to assess the water quality, speciation of heavy metals in sediments and water, and the drinking water treatment plant in an important Algerian reservoir (Timgad dam, Batna). Algeria has invested billions of dollars in large seawater desalination plants and dams; however, the water quality remains a serious issue, hence this research. The high concentration (≥ 400 mg/l) of sulfate and the depth (44 m) of the studied reservoir leads to sulfate-reducing bacteria (SRB) activity and water stratification, influencing the sulfur S cycle and metal speciation. The total and sequential extractions, using the method of the European Community Bureau of Reference (BCR), were applied to characterize seven metals in sediments and coagulation sludge. It showed the absence of Zn and only trace levels of other metals in the water, whereas the sediment and the decanter sludge were highly contaminated, especially by Fe and Zn (2100 to 2800 mg/kg); the other metal concentrations were much lower. The absence of Zn in aqueous phases and its high concentration in the solid phases turned out to be a serious paradox and issue of this research work. The compositions of the reservoir sediments and coagulation sludge (decanter sludge) were similar, suggesting the metals travel through turbidity, from reservoir to treatment plant and the potential drinking water contamination. This metal characterization, combined with speciation predictive software, will allow a better understanding of heavy metal behavior and fate.