Assessment of selected macroalgae for use in a biological hybrid system for treating sulphur in acid mine drainage (AMD)

Filamentous algae biomass is very limited in aerobic constructed wetlands and totally absent in anaerobic constructed wetlands. Its contribution to the removal of sulphur from acid mine drainage will therefore rarely reach a significant level if not used in association with secondary algae treatment ponds as part of a biological hybrid treatment system. Although a high sulphur concentration has a lower environmental impact than dissolved metals and acidity, it does have an adverse impact on water quality. The current study employed selected macroalgal species under laboratory conditions to determine the bioaccumulation of sulphur (S) and other important algal growth elements such as calcium (Ca), magnesium (Mg) and phosphorus (P) from acid mine drainage (AMD) water and treated constructed wetland water at different pH values. Following exposure of the macroalgae to AMD and treated constructed wetland water for 192 h, Microspora tumidula showed the highest bioaccumulation of S and P which occurred at a pH of 5. Oedogonium crassum showed the highest bioaccumulation of Ca and Mg at a pH of 7. The results also showed that the accumulation efficiency of Mg by all three macroalgal species increased significantly as the pH increased. The filamentous species Oedogonium crassum and Klebsormidium klebsii showed very little increase in chl-a (mg g−1 fw) and ash free dry weight (mg g−1 AFDW) after exposure to the mine and treated constructed wetland water after 192 h at all four pH ranges in comparison to the species M. tumidula. However, the species M. tumidula show significant increases in both chl-a (mg g−1 fw) and mg g−1 AFDW at pH values 5, 6.14 and 7. The study established that the species M. tumidula is a good candidate for use in a biological hybrid system for treating sulphur-rich acid mine drainage.