Comparative Assessment of Performance of Aluminium Sulphate (Alum) and Ferrous Sulphate as Coagulants in Water Treatment

Alum and ferrous sulphate, being among the best-known coagulants in water treatment were investigated with the aim of determining their coagulation efficiencies. The parameter levels of a turbid water were determined before and after treatment with alum and ferrous sulphate respectively at coagulant dosages of 1 to 10 g per 3 litres of turbid water, for each of the following parameters: pH, total suspended solids (TSS), dissolved oxygen (DO), biochemical oxygen demand (BOD5), turbidity, chloride, fluoride, phosphate and chemical oxygen demand (COD). The turbid water was prepared by addition of ground humus soil to tap water. Using a sedimentation beaker, experiments were conducted, leading to optimum coagulant dosage in some parameters. Coagulation experiments of the turbid water at the coagulant dosage of 10 g per 3 litres, gave the following coagulation efficiencies with alum as the coagulant: pH (44.92%), TSS (98.71%), DO (90.10%), BOD5 (100%), Turbidity (98.70%), chloride (100%), fluoride (100%), Phosphate (80%), COD (100 %) and Copper (0.00%). Similarly, using ferrous sulphate coagulant for the same level of turbid water and same dosage, the coagulation efficiencies achieved were: pH (57.24%), TSS (96.54%), DO (96.31%), BOD5 (100%), Turbidity (96.77%), and chloride (100%), fluoride (100%), phosphate (91.11%), COD (100%) and Copper (0.00%). The results showed that increasing coagulant dosage enhances water quality with respect to all the parameters studied. Furthermore, the results indicated that pH, DO, BOD5, fluoride, phosphate and COD mean % efficiencies were higher for ferrous sulphate coagulant in comparison with alum. On the other hand, alum displayed better coagulation efficiency than ferrous sulphate in the following parameters: TSS, turbidity and chloride. The overall results of the coagulation studies applying increasing coagulant dosage revealed that coagulant efficiency is parameter dependent. The outcome of this work can be an important guide to water treatment operators.