The potential utilisation of indigenous South African grasses for acid mine drainage remediation

B Ramla,C Sheridan

doi:10.4314/wsa.v41i2.10

Abstract

Acid mine drainage (AMD) is a significant threat to the environment in South Africa and needs to be remedied. Although active treatment methods have been and are being implemented in industry, passive treatment systems involving bioremediation have the potential to be a more cost-effective and environmentally sustainable solution. Biological treatment of AMD involves the reduction of sulphate to sulphide by sulphate-reducing bacteria in the presence of a suitable organic substrate. This study tested the potential for indigenous grasses to be used as a carbon source in the bioremediation of AMD. Bioreactor experiments were conducted over a 70-day period to investigate whether indigenous grasses can be used to effectively reduce sulphate and iron concentrations, and increase the pH of an AMD solution. The results indicated that indigenous grasses hold promise for remediating AMD, as a maximum of 99% iron removal, 80% sulphate removal, and a final pH of 8.5 was achieved from initial conditions of 2 000 mg/l iron, 6 000 mg/l sulphate, and a pH of 3. Optimal results occurred in the bioreactor with Hyparrhenia hirta grass amended with soil containing microbes, although all bioreactors effected some form of remediation compared to the control.

Highlights

In South Africa, the mining industry is a key driver of the economy
We investigate the potential use of two indigenous grasses (Hyparrhenia hirta and Setaria sphacelata) as an organic substrate for treating acid mine drainage (AMD) through the mechanism of dissimilatory sulphate reduction (DSR)
The data indicate that the pH of the AMD in bioreactors with organic substrates increased during the 70-day period

Summary

Introduction

In South Africa, the mining industry is a key driver of the economy. South Africa possesses large natural reserves of various metals and coal, and hosts substantial mining activity (McCarthy, 2011). As a consequence of the types of ores in South Africa, which are often sulphide-based, mining operations, currently operational and abandoned, have led to the formation of acid mine drainage (AMD). AMD is a discharge from mining operations which is highly acidic and contains high concentrations of metals and sulphates (Manders et al, 2009). Acid mine drainage occurs naturally when sulphur-rich minerals from mining operations are exposed to air and water, and undergo oxidation of sulphur-based mineral (such as a pyrite). This results in the formation of sulphate and a reduction of the pH of the aquatic medium. Complete discussions of the formation of AMD and the problem of decant in the Witwatersrand basin are available (McCarthy, 2011; Sheridan, 2013)

Methods

Results

Conclusion