Assessment of mercury removal efficiency of a constructed wetland system from gold mining

Background. Mercury (Hg) contamination resulting from gold mining is an environmental problem caused by its ability to affect ecosystems and human health. Therefore, it is essential to propose alternatives focused on reducing the pollution produced mainly to water resources, due to the persistence and permanence of this heavy metal in the environment. Goals. This study evaluated the removal of Hg and the organic load of wastewater from a mining plant through a horizontal subsurface wetland flow system. Methods. The physicochemical characterization of the mining sewage was carried out, in addition, a system of three wetlands was designed and operated in which the Hydraulic Retention Time (HRT) and the plantation of Heliconia psittacorum were varied, then, parameters such as pH, OD, turbidity, BOD5, COD and Mercury were studied. An ANOVA statistical test with significance of 95% was applied. Results. The mining effluent showed COD and Hg concentrations of 197 mg O-2/L and 0.0021 mg/L, respectively, values which are higher than those permitted by Colombian and EPA regulations. The wetlands evaluated showed removal efficiencies for turbidity, BOD5, COD and Hg higher than 98.44%, 93.10%, 71.52% and 91.03%, respectively. The statistical tests suggest that there is no significant difference in the TRH (p=0.361), therefore it is possible to operate the wetland system with 2 days of treatment. In addition, significant differences were found between the planted wetlands and those composed only by the support bed (p=0.039). Conclusions. Horizontal subsurface flow wetlands and Heliconia psittacorum are highly efficient in the removal of Hg from gold mining wastewater, as a for environmental bioremediation.