Finding effective, environmentally friendly ways to conserve our Water sources
Water is undoubtedly one of our most valuable and most constrained resources on earth. Despite earth’s abundance of water, precious little of this resource is safe for human consumption. Safeguarding water sources is, therefore, a key concern for us at Gem Diamonds, in line with our duty of care.
In line with our objective of conserving water sources, at our Letšeng mine, remediating water contaminated with nitrates is a key priority in our water management strategy. Over the years, a number of methods have been examined. One such method was the construction of an engineered wetland in the Qaqa Valley. The wetland construction commenced in late 2012 to test the hypothesis of the capacity of wetlands to treat elevated nitrates effectively. Unfortunately, due to the smaller and hardier vegetation indigenous to the mountainous areas surrounding our Letšeng mine, the plants were unable to absorb and use the nitrates present in the water at the rate necessary for remediation to occur at this point. We anticipate that results will improve as the wetland continues to establish itself over a longer period. The wetland has, however, served as an environmental offset area, having been restored after historical artisanal mining destroyed the area. Environmental offsetting is an intervention that seeks to counterbalance an adverse impact on one location by intervening at another location to deliver an environmental benefit.
Other methods of denitrification were subsequently explored. One such method, similar to the use of the wetland but different in application, is that of fertigation. Fertigation involves the use of wastewater supplied to plants through an irrigation system. Denitrification occurs when soil bacteria use nitrates for their respiration in the place of oxygen in the air. This process occurs most rapidly in warm, wet soils. This denitrification has the positive benefit of lowering the nitrate concentration in the water returned to the system. However, due to the colder weather experienced at our Letšeng mine, the denitrification process may be affected. Trials to determine the effectiveness of this method are ongoing.
One of our more promising denitrification trials is our bioremediation plant. In June 2015, a team from the University of the Free State conducted field testing at Letšeng to analyse the viability of such a project. Bioremediation is a strategy that uses naturally occurring organisms to break down pollutants such as nitrates into less toxic substances. Species in the bacterial genus Pseudomonas present high potential for bioremediation. During testing, the team discovered a dominance of Pseudomonas species in the water – this meant that naturally occurring bacteria could be used, rather than introducing an alien species, which may endanger the ecosystem in the long run.
A bioremediation pilot plant was subsequently set up. Although many challenges were initially faced, including a large amount of sediment in the water impacting the flow of water through the system, once these issues were dealt with, we began to collect data to monitor the plant’s effectiveness. This method of remediation is especially appealing due to its environmentally friendly nature. Not only does it create less waste than more expensive methods, such as reverse osmosis, but it is also more cost efficient and is not labour intensive. This exciting project could be extended to other mines facing more serious nitrate or other contaminant issues than those at Letšeng, as well as other industries that face similar issues.
To date, the bioremediation plant has supplied very promising results, with 90% to 99% of pollutants (nitrates) removed from the water. Large-scale application of this project is currently being explored to ascertain its viability in treating contaminated water leaving the mine site.
|Interior of the bioremediation plant at Letšeng.|