The Role of Inorganic Metal Salts in Wastewater Clarification

Abstract

An investigation into the ability of four inorganic coagulants namely; alum (Al2(SO4)3.18H2O), ammonium aluminum sulphate (NH4Al(SO4)2.12H2O), ferrous sulphate (FeSO4) and ammonium ferrous sulphate (NH4)2Fe(SO4)2.6H2O) in clarifying wastewater was examined. Results obtained from conventional standard ‘jar-test’ experiments indicated that alum was the most effective coagulant since it reduced turbidity of the wastewater to 0.64 NTU at a contact time of 300 min. Ferrous sulphate was the least effective coagulant, reducing turbidity of the wastewater to 3.45 NTU only at 240 min contact time, but when the contact time of the experiment was increased from 240 to 300 min, re-coloration of the solution was observed indicating re-stabilization of suspended particles. These findings tend to support the claim that alum is a choice coagulant for wastewater clarification.