The feasibility of a permeable reactive barrier to treat acidic sulphate- and nitrate-contaminated groundwater

Abstract

Manufacturing of fertilisers at a site in Johannesburg, South Africa, has resulted in the localised contamination of the shallow groundwater. The latter migrates through the weathered granite zone and emerges as base flow to the natural drainage system that ultimately exits the site. The water quality is acidic and is contaminated with respect to nitrate, sulphate, aluminium, fluoride and manganese. Treatment of this water is therefore necessary before discharge.
In situ passive rehabilitation of groundwater using a permeable reactive barrier offers a potentially cheaper alternative to conventional treatment technologies for acidic groundwater. Feasibility criteria used in this study were based on the suitability
of the site for the installation of a permeable reactive barrier (PRB) and on the amenability of contaminants for treatment using locally available reactive media. The suitability of the reactive media was assessed from laboratory leach tests on reactive
materials (mushroom compost, dolomite and limestone). These tests were followed by batch testing of various composites of the mushroom compost and the neutralisation gravel media (dolomite and limestone for comparison).
The results of the study indicated that the site conditions were potentially suitable for the installation of a PRB but that the mushroom compost is not suitable as a carbon source. This was indicated by the limited success achieved in reducing sulphate concentration and the poor quality of the leachate with respect to sodium, chloride, ammonia and potassium. The neutralisation
capacity of the dolomite aggregate was similar to that of the limestone for the batch tests. However, it can be expected that the long-term performance would be inhibited by clogging and armouring by aluminium and manganese precipitates.

Water SA Vol.32 (2) 2006: pp.129_136