Bioremediation of acid mine drainage contaminated soils using bioattenuation, wastewater and air-injection system

Abstract

Acid mine drainage (AMD) poses a serious challenge to the ecosystem due to its disastrous effect on soil and water resources which contributes to the pollution and reduction of the accessibility of potable water and arable land for agricultural activities. The treatment of contaminated soils using physical, chemical, or thermal methods requires some improvements to meet the required remediation purpose. The purpose of this study is to investigate the application of bioattenuation, wastewater, and air-injection for the remediation of AMD polluted soils. A microcosm comprising 1 kg of polluted soil was amended with varying loadings of domestic and brewery wastewaters for biostimulation treatments, and the bioattenuation received no amendment while the bioventing treatment was supplied with wastewaters and atmospheric air at 3 L/min for 30 mins intervals every 48 h. The investigation conducted under the ambient condition for 28 days recorded average metal removal efficiencies of 12–31% (bioattenuation), 50–66% for all heavy metals (iron, aluminum, copper and zinc) except manganese (28%) (biostimulation) and 56–70% (bioventing) while 32%, 35% and 52% sulfate removal efficiencies were recorded for bioattenuation, bioventing and biostimulation respectively. The study revealed that wastewater and bioventing systems can be efficiently utilized as an eco-friendly approach for the treatment of acid mine contaminated soils and pollution mitigation in the mining environments. In addition, from a comparative point of view, the results of the study further showed that the amendment of wastewater is more effective for sulfate removal while air injection enhanced metal removal from acid mine drainage contaminated soils. The synergetic effects have also been observed; the current study demonstrates that the combined application of biostimulation and bioventing system requires constant monitoring to ensure the provision of appropriate anoxic conditions for biosulfidogenic activity by enhancing sulfate removal while promoting an oxic environment for the oxidation process to facilitate metal removal for the effective treatment of acid mine drainage contaminated soil.