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 (BOD5), chemical oxygen demand (COD), [Cr6+] 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 T5, pH value 7.13 was found in treatment T7 followed by 7.23 in T2 and T6, 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. Cr6+ concentration was reduced considerably in treatment T5 (0.03 mg/L) and T7 (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 (T5) as well as alum (T1) for the effective primary treatment of tannery effluents.Key words: Coagulation, alum, lime, ferric chloride, biological oxygen demand (BOD5) and chemical oxygen demand (COD)

Flood Damage Assessment: A Review of Flood Stage-Damage Function Curve

Nowadays, flood control has been replaced by flood management concept in terms of living with flood, making benefit of it, and minimizing its losses. The success in flood management in any region depends on the evaluation of different types of flood losses. For the assessment of flood damages, this requires the use of stage–damage functions for different categories of land use. A review is presented of the methods used to construct stage–damage function curves for residential, commercial, agricultural, and industrial category. Two main approaches in constructing stage–damage functions are empirical approach, which is based on damage data of past floods, and synthetic approach, which uses damage data collected by interview survey or questionnaire. For a developing country like Malaysia which has limited history and actual flood damage data, the synthetic method is the preferred approach in constructing stage–damage function curve