Oxygen Dynamics and Carbon Removal in Municipal Waste Stabilization Ponds in Arctic Regions
Abstract Waste Stabilization Ponds (WSPs) are commonly used for municipal wastewater management in Canadian Arctic communities. However, there has been limited research on WSP performance in these regions, and how environmental and operational factors influence treatment processes in arctic WSPs. New wastewater discharge standards have been proposed for all Canadian municipalities and, with respect to arctic municipal wastewater treatment solutions, it is unclear if WSPs are capable of meeting these standards. The objectives of this research were to (i) characterize the performance of WSPs currently operating in arctic regions, (ii) identify environmental and operational variables that influence biological treatment processes, and (iii) develop recommendations for the design and upgrading of future and current arctic WSP systems. Four operational WSPs in the Canadian Arctic Territory of Nunavut were intensively monitored during a four year (2011-2014) period. The four WSPs were generally anaerobic, resulting in poor removal of carbonaceous biological oxygen demand (CBOD), with average effluent CBOD5 concentrations exceeding 80 mg/l. A series of controlled mesocosm experiments were conducted to identify how environmental conditions (temperature and irradiance) and organic carbon loading variables influenced algae growth, oxygen dynamics and CBOD5 removal rates. A process-based model was also developed to simulate oxygen dynamics and carbon removal and was successfully calibrated and validated using the experimental data. The experiments and process-based modeling demonstrated that the development of aerobic conditions, and increased rates of CBOD5 removal was directly linked to the presence of an active algae population. The results also indicated that current organic loading rate guidelines adapted from non-arctic regions are not applicable, and that both initial carbon concentrations and daily areal carbon loading rates need to be decreased in order to facilitate aerobic environments in arctic WSPs. WSPs operating in cold climates are very sensitive to changes in operational and environmental conditions, and greater resiliency needs to be incorporated into design guidelines in order to meet more stringent discharge criteria.