Efficiency of different coagulants combination for the treatment of tannery effluents: A case study of Bangladesh

This study has focused on the physico-chemical parameter of tannery effluents as well as the treatment efficiency of alum, ferric chloride and lime, addressed as different treatments. Sample collection and analysis were performed using standard method. Pollutant removal efficiency was measured in terms of reduction in value of total solid (TS), suspended solid (SS), total dissolved solid (TDS), color, pH, [Cl - ], Alkalinity, biological oxygen demand (BOD 5 ), chemical oxygen demand (COD), [Cr 6+ ] and salinity. While analyzing the physico-chemical parameters of the tannery effluents, before treating with coagulants, the odor of the effluents was found to be invariably objectionable. After treatment of the tannery effluents, the lowest value for color (246.67 in Hazen unit) was found in the treatment T 5 , pH value 7.13 was found in treatment T 7 followed by 7.23 in T 2 and T 6 , the lowest TS (3833.33 mg/L) was recorded in the treatment T5 and SS observed as 0 mg/L in case of both T5 and T1 treatments. Cr 6+ concentration was reduced considerably in treatment T 5 (0.03 mg/L) and T 7 (0.07 mg/L). Reduction in values of TDS, alkalinity, salinity, Cl - , BOD5 and COD in treated effluents was also notable. The study recommended the combination of alum and ferric chloride (T 5 ) as well as alum (T 1 ) for the effective primary treatment of tannery effluents. Key words: Coagulation, alum, lime, ferric chloride, biological oxygen demand (BOD5) and chemical oxygen demand (COD).