Assessing the performance of horizontally flowing subsurface wetland equipped with Vetiveria zizanioides for the treatment of acid mine drainage

Abstract

Contamination of different ecological spheres with acid mine drainage (AMD) has raised numerous concerns in countries with well-developed mining industries, thus calling for urgent intervention measures to redress the prevailing water pollution challenges. Due to its chemical composition and (eco)-toxicological nature, AMD can pose severe environmental damage if not properly managed. Herein, the performance of subsurface horizontally flow constructed wetland (SSHF-CW) equipped with Vetiveria zizanioides for the treatment of AMD was explicitly assessed. To fulfill the goals of this phytoremediation study, the experiments were administered for a period of 30 days using authentic AMD from an active gold mine; and the quality of the feed and product water was monitored daily. The results showed a slight increase in pH from 2.4 to 4.01 and a net reduction in electrical conductivity, total dissolved solids, and sulphate, registering ≥ 47.20%, ≥ 46.00%, and ≥ 33.04%, respectively. Thenceforth, there was a net removal of metal in the following order; Zn (77.75%) ≥ Fe (75.36%) ≥ Mn (67.48%) ≥ Al (55.05%) ≥ Ni (44.01%) ≥ Cu (11.36%). Interestingly, the obtained results demonstrated that Vetiveria zizanioides was tolerant to AMD with a tolerance index of 1.23 after 30 days, while the removed metals were partitioned amongst the substrate, plant matrices, and external factors. Chemical species accumulated by the plants were more concentrated in the roots except for Mn, which was more concentrated in the shoots. The X-ray fluorescence and X-ray diffractometers analyses revealed the presence of chemical species in the substrate, while Fourier transform infrared and scanning electron microscopy-energy dispersive spectroscopy analysis revealed the presence of chemical species in plants roots, confirming that substrate and plants play a huge role in pollutants removal. As such, it can be concluded that SSHF-CW equipped with Vetiveria zizanioides plays a major role in the removal of contaminants from AMD and could be employed in derelict mines or small operations as a passive treatment technique to phyto-remediate mine effluents.

Keywords

• acid mine drainage
• horizontal subsurface constructed-wetland
• vetiveria zizanioides
• emerging treatment technique
• phytoremediation