Abstract

"This investigation evaluated the efficiency of primary coagulants, such as Ferrous sulfate (FeSO4 ‧7H2O), Ferric chloride (FeCl3 ‧6H2O) and Calcium hydroxide Ca (OH)2 as a coagulant aid. These chemical coagulants were used in different doses and combinations to reach the optimization of the coagulation and precipitation process, in terms of removal of chromium and other undesirable pollutants, such as ammonia, chlorides, sulfates, Chemical Oxygen Demand (COD), Total Suspended Solids(TSS), Total Dissolved Solids (TDS), hydrogen sulfide gas(H2S). The study was conducted during October 2013 – November 2014. The correlation Pearson between all indicators of raw effluents showed that Total alkalinity and ammonia ions(r = 0.896), TSS and NH4+ (r = 0.869), TSS and Cl- (r = 0.883), sulfate and pH, NH4+, TSS respectively, (r = 0.821), (r = 0. 807), (r = 0.824), H2S and COD (r =0.918) were strongly positively correlated. The correlation Pearson between all indicators of treated effluents showed a very strong correlation between E.Coli and St.Faecalis (r =0.992), also Total alkalinity and COD, chromium, respectively with (r = 0.918), (r =0.883), chromium and COD(r = 0.947), were strongly positively correlated. FeSO4 seemed to be less effective than FeCl3, with regard to the SVI. The Sludge Volume Index was the only parameter that was weakly negatively correlated with other parameters. This study concluded that the chemical combination of FeSO4 and Ca(OH)2 at 150 mg/L and 1000mg/L was more effective than FeCl3 and Ca(OH)2 for the treatment of the tannery effluents with a high efficiency in the removal of chromium, E.Coli and St. Faecalis, ammonia ions, chloride, H2S, TSS, COD and sulfate. A small disadvantage was observed with regard to the COD and TDS. "

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