Distribution of aluminium from alum sludge in water and sediment

Abstract

Aluminium sulfate is generally used as a primary coagulant in most municipal water treatment plants. The sludge produced is often discharged back into the river. Depending on the physicochemical properties of the river water, aluminium from the sludge will become soluble and form various species that may be toxic to aquatic life. This study is an attempt to look at the effect of alum sludge dumping on the distribution of various aluminium species in the Linggi River of Negeri Sembilan, Malaysia, which is used as source of raw water for the Linggi Water Treatment Plant. The result showed that the total aluminium concentrations in the five sampling stations located upstream and downstream of the dumping point along the river were 0.48-1.14 mg L^-1, of which labile aluminium was 0.37-0.56 mg L^-1 and non-labile aluminium was 0.12-0.58 mg L^-1. Statistical analysis indicated that there was no significant difference in aluminium concentration in the water along the river. However, total aluminium concentration in the sediments increased significantly downstream from the water plant, indicating that aluminium from the sludge dumping may accumulate in the sediment.