Kinetic Study of Aluminum Sulphate and Ammonium Aluminum Sulphate Coagulants in Wastewater Treatment

Abstract

An investigation into the kinetics of two inorganic coagulant namely: aluminum sulphate octadecahydrate (Al₂(SO₄)₃.18H₂O) an ammonium aluminum sulphate dodecahydrate (NH₄Al(SO₄)₂.12H₂O) was studied to determine the effect of certain kinetic parameters on coagulation performance of the above mentioned coagulants. Results of analysis obtained revealed that the rate constant (k) for Al₂(SO₄)₃.18H₂O was 5.727s^-1, while that for NH₄Al(SO₄)₂.12H₂O was 2.282s^-1. However, the order of the reaction (x_n) of Al₂(SO₄)₃.18H₂O and NH₄Al(SO₄)₂.12H₂O with the wastewater was 1.0 and 1.0, respectively, indicating that both reactions were first order. Considering the mechanism of the reaction, the general trend observed indicated that the Al₂(SO₄)₃.18H₂O reaction was thrice as fast as the NH₄Al(SO₄)₂.12H₂O reaction. This fact together with the larger value of k for Al₂(SO₄)₃.18H₂O obtained in the experiment lend credence to the widely held believe that Al₂(SO₄)₃.18H₂O is a more effective coagulant than NH₄Al(SO₄)₂.12H₂O in wastewater treatment.