Evaluation of Residual Al3+ and Fe3+ Concentration in Blended Alum-Ferric Chloride Coagulant Use

Abstract

The use of aluminum and iron salts as coagulants in water treatment may cause the rise of aluminum and iron ions concentrations in finished water. Approximately drinking water is responsible for nearly five percent of the aluminum ingested by humans although aluminum accumulation in the brain is associated with neurodegenerative diseases. This study aims to evaluate the residual concentration of Al3+ and Fe3+ upon the use of blended alum-ferric chloride coagulant in clarifier effluent. An experimental study of Jar tests were conducted to evaluate the effect of blended alum-ferric chloride coagulant use on the finished water residual aluminum and ferric ion concentration. All parameters were determined according to APHA standard methods for water and wastewater examination. Data were compiled and analyzed using Microsoft excels 10 and Minitab 16 and presented using tables and graphs. As compared to single coagulant use, 1:1 A-FC (Alum-Ferric chloride) mix-use resulted in an average of 40% aluminum ion concentration and 20% residual ferric ion concentration reduction. At optimal pH and dose, the residual aluminum ion concentration were 0.1 mg/L, 0.06 mg/L and 0.09 mg/L for alum, 1:1 and 3:1 A-FC coagulants, respectively. While, the ferric ion concentration were 0.4 mg/L, 0.32 mg/L and 0.11 mg/L for ferric chloride, 1:1 and 3:1 alum-ferric chloride coagulants, respectively. The study demonstrated a strong correlation (r=0.93) between coagulant dose and residual aluminum ion concentration which was statistically significant (P<0.05). Also, a strong correlation (r=-0.97) was observed between the water pH and residual aluminum ion concentration which was similarly statistically significant (P<0.05). The residual aluminum and ferric ion concentrations were greatly reduced when alum and ferric chloride coagulants were used in combinations than used separately. The regular monitoring of chemical residuals in drinking water and control of coagulant conditions should be considered in the water treatment process.