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Alum sludge was characterized to explore the feasibility of coagulant recovery using hydrochloric acid and its application as an alternative for the commercial coagulant. The composition of alum sludge from ESZ-WTP is a reflection of the structure of the virgin coagulant used in the treatment process and the contaminants in raw water. The analysis of sludge collected from ESZ-WTP showed that the average values of the water and organic contents were 86% and 25%, respectively. In addition, Table 2 shows the concentrations of metals in the sludge collected from ESZ-WTP. As shown, the major metal constituents of the sludge were aluminum 13.3%, iron 2.2%, and calcium 1.2%. These are nearly the same constituents of the commercial alum used in the treatment process. This indicates that the main source of metals in the sludge is the coagulant used in the treatment and not from raw water.

Table 2

Concentration of different metals (expressed in gram of metal per 100 g sludge on dry mass basis) in sludge samples collected from the drying lagoons of the ESZ-WTP

Metal Al Ba Co Cr Cu Fe Li 
Conc. 13.34 0.01 0.002 0.013 0.001 2.21 0.001 
Metal Mn Ni Pb Sr V Zn  
Conc. 0.27 0.004 0.087 0.017 0.012 0.011  
Metal K Na Ca Mg    
Conc. 0.216 0.164 1.203 0.902    
Metal Al Ba Co Cr Cu Fe Li 
Conc. 13.34 0.01 0.002 0.013 0.001 2.21 0.001 
Metal Mn Ni Pb Sr V Zn  
Conc. 0.27 0.004 0.087 0.017 0.012 0.011  
Metal K Na Ca Mg    
Conc. 0.216 0.164 1.203 0.902    

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