Softening of groundwater in the eastern region of the Northern Algeria Sahara: Case of the Biskra region
In Biskra drinking water supply for inhabitants and the irrigation of crops are based on the exploitation of the groundwater aquifers of the northern Sahara. One of the major challenges for the sustainability of use of this resource is water quality of some aquifers (phreatic and Miopliocene). These are highly mineralized (between 2 and 3 g∙L‐1 of dissolved salt), the dominant chemical facies being sulphate-chloride with an excess of chlorides higher than the World Health Organization (WHO) standard (250 mg∙L‐1). To remedy this problem of salinity and in order to develop a reliable and economically sustainable softening technique, we have tested two partial softening processes in this work, coagulation-flocculation with aluminum sulphate on the one hand and precipitation with slaked lime Ca(OH)2 on the other. The main results confirm that the removal of chloride ions is low for both tested processes, 29.7% and 19.1% respectively. We have also demonstrated that water treatment with slaked lime was more efficient, sulphate ions being reduced to 73.3%. However, this process increased the pH of the treated water and required a subsequent pH adjustment. Similarly, the concentration of bicarbonate ions decreased by about 85% because the use of slaked lime acts not only on chlorides and sulphates associated with calcium and magnesium ions, but also on the bicarbonate ions. These tests were also used to justify the choice of the most appropriate method technically and economically for softening water in the study area