Ammonia Nitrogen Removal by Enhanced Algae Growth – Case Study of a Subarctic Mine Site

Elevated concentrations of ammonia nitrogen is a common characteristic of mine impacted water and generally results from the dissolution of undetonated explosives (i.e., Ammonium Nitrate and Fuel Oil and emulsion explosives) by contact water. Several active water treatment technologies are commercially available to remove ammonia nitrogen, but reduction of active treatment demand by promoting natural attenuation is considered best industry practice. In this paper, the results of laboratory-scale and full-scale trials of a semi-passive approach (i.e., enhanced algae growth) to remove ammonia nitrogen at the Meliadine mine are presented. Phosphorus was found to be the limiting factor to algae growth at the mine site. The addition of various concentrations of phosphorus was first tested at a laboratory scale. The samples were exposed to in-situ conditions, and ammonia nitrogen removal rates ranging from 40% to 93% were achieved over a period of 24 days. This paper also presents the methodology and results of an in-pond treatment during which a 50% ammonia nitrogen removal rate was observed after 68 days. The studied mine site uses breakpoint chlorination as its primary treatment approach for ammonia nitrogen removal. The results presented in this paper show the potential of using enhanced algae growth as a pre-treatment method, subsequently reducing the quantity of chemicals required for operating the breakpoint chlorination plant. This potential requires further investigation and additional trials are currently under evaluation.