Abstract
New regulations have increased the level of treatment required before mining effluent can be discharged. In particular, new federal regulations have stipulated that ammonia, a compound that can be toxic to freshwater organisms such as fish, must be removed to non-toxic levels prior to discharge. Furthermore, many mines are facing regional limits on effluent nitrate discharge. Nitrate is a compound that can contribute to the eutrophication of natural water bodies as well as contaminate drinking water sources. It is therefore important that the treatment systems be developed to remove ammonia and nitrate from mining effluent, and that those systems be tailored for the unique operating conditions of mining sites.
In this presentation, we will discuss a novel biological treatment method for the simultaneous removal of ammonia and nitrate. The presentation will include performance results from a large-scale pilot system at a gold mine in Northern Ontario.
Compared to conventional biological processes, which typically separate the ammonia and nitrate removal processes into two-four stages, this novel process requires only one-two stages because the ammonia and nitrate removal mechanisms are performed simultaneously. Furthermore, the novel biological treatment method is based on microorganisms that are much more resilient than conventional ammonia oxidizing microorganisms, meaning that the novel biological treatment method responds better to both temperature variation and upset conditions. For example, if the biological pre-treatment system were to intermittently produce over >0.5 mg/l effluent copper, the novel biological treatment method would respond/adapt/recover faster than conventional biological ammonia removal to the potentially inhibitory copper concentrations.
The novel biological process does require more carbon supplement than conventional biological ammonia and nitrate removal processes, and therefore also produces more biosolids. However, the biosolids are an organic by-product of the treatment process and can potentially be stockpiled for beneficial re-use during mine closure. Additionally, although the carbon supplement required is higher for the novel treatment method, other chemical demands for alkalinity supplement and pH adjustment are significantly lower than in conventional ammonia and nitrate removal.
Overall, the novel ammonia and nitrate removal process provides a viable alternative for the biological removal of ammonia and nitrate from mining effluent in the Canadian context.