Disinfection performance in wastewater stabilization ponds in cold climate conditions: a case study in Nunavut, Canada

Passive wastewater treatment systems are commonly applied in northern Canadian communities. Pathogen removal in these systems, which relies on natural purification, can be greatly affected by Arctic environmental conditions. In 2012, new Wastewater Systems Effluent Regulations (WSER) were implemented in Canada, but not in the far North due to the number of northern communities with limited wastewater treatment infrastructure which could present a challenge in achieving these criteria. In the summer of 2015, two sampling trips were undertaken to Pond Inlet (Nunavut) to study the disinfection performance of a single-celled wastewater stabilization pond (WSP). Sunlight disinfection was only effective close to the water surface, as UV and photosynthetically active radiation (PAR) were completely attenuated within the first 5-10 cm of the water column. The system achieved 0.76-1.28 log removal of E. coli, 0.81-1.00 log removal of fecal coliform and 0.79-1.02 log removal of total coliforms during the treatment season. The average E. coli concentration in the WSP was 1.3x10 CFU/100mL prior to annual decant, which exceeded discharge standards set by the Nunavut Water Board. Existing WSP disinfection models were selected to assess their viability to predict the performance of Arctic WSPs. In general, the models over predicted disinfection performance by an order of magnitude or more, and some were unable to replicate trends in the data. A modified model for polar WSPs should be developed, as existing models were designed for temperate or tropical regions.