Update on 3 years of successful commissioning and operation of a demonstration-scale constructed wetland treatment system (CWTS) at the Minto Mine, Yukon
Mr Ryan Herbert, Bryanna Eisner, Rachel Martz, Dr Vanessa Friesen, Dr Monique Simair
The Minto Mine is an open pit and subsurface copper mine located in the Yukon Territory. As part of the Reclamation and Closure Plan a constructed wetland treatment system (CWTS) is being designed and implemented through a phased approach. This talk will update on the past 3 years of commissioning and operation of the on-site demonstration-scale CWTS. Throughout the CWTS operational period, treatment achieved average outflow concentrations (dissolved) of: cadmium - 0.0092 ug/L, copper - 17.3 ug/L, molybdenum - 2.3 ug/L, selenium - 0.5 ug/L, and zinc - 1.9ug/L. Additionally, cadmium was often treated to below detection limits, nitrate was treated, and some sulphate treatment was also observed. As designed, treated constituents were transformed into stable minerals within the wetland sediments. Plant uptake of constituents was minimal throughout operation, and a high abundance of beneficial microbes associated with ongoing passive treatment were identified in the CWTS. Importantly, there was no discernible difference in treatment according to temperature (even under ice cover). The CWTS generally operated with a hydraulic retention time (HRT) of ~6 days, however, some constituents achieved a thermodynamic minimum within the system by half this time, suggesting 2 – 4 days HRT would be sufficient for treatment.