LaRonde Successfully Reduces Effluent Nitrogen Levels
For the past three years, the water treatment team at LaRonde has been testing different denitrification processes at its biological plant to determine which one works best at reducing the amount of nitrogen in the mine’s final effluent.
What exactly is denitrification? It is a biological process whereby, “nitrogen is removed from water.”
Why is it so important to reduce the amount of nitrogen in LaRonde’s effluent? While nitrogen can be found throughout nature and the environment, high levels of nitrogen entering natural waterways can result in excessive algae growth. Since the effluent from the Laronde mine eventually makes its way to nearby Lac Preissac where cottages abound and recreational fishing is practiced.
From a prevention point of view, the Canadian government has been considering amending the Metal Mining Effluent Regulations (MMER) to include a nitrate standard. While it has yet to determine what form the standards will take or when they will be introduced, the team at LaRonde wanted to ensure they had the right solutions in hand.
Patrick Laporte, Water Treatment Coordinator at LaRonde says, “We wanted to test various nitrate treatments in advance, so that we could be ahead of any potential regulations and quickly comply within any required time limits. In the future, we also anticipate that any imposed limits will continue to go lower and lower, and require more and more follow up. We wanted to do the necessary research and development work to ensure we could keep pace.”
The team tested three different types of denitrification with various carbon sources, to identify the process that would work best at treating the nitrates produced at the existing thiocyanate water treatment plant, also using bacteria
While two of three processes tested worked well, the team selected the process that reduced the nitrate levels in a cost efficient way, , used fewer chemicals, did not require extra sources of carbon and resulted in a cleaner effluent.
In December 2017, LaRonde retrofitted two reactors at its biological treatment plant with to the new process. It has already led to a 15 to 20% drop in nitrate levels. We expect to eventually reach a reduction between 20% and 40%.
“We can now reduce the levels of nitrate in our effluent and we are working at reducing the load of all contaminants released to the environment, in a continuous improvement mode,” comments Patrick. “Our team will continue to do research and advance our knowledge in this area so that we can continue to improve our process, reduce costs and reduce LaRonde’s environmental footprint.”