An analysis of phosphorus cycling in waste stabilization ponds (WSPs) in Nunavut

Abstract

This study examined the forms of and amounts of phosphorus (P) present in water and sediment samples taken from two arctic climate waste stabilization ponds (WSPs) located in Kugaaruk, and Pond Inlet, Nunavut. This information was used to determine the primary mechanisms for P removal from the water column in these types of systems. The central hypothesis was that the dissolved P in the WSPs is removed by precipitation with cations and by algal or bacterial assimilation. The study was exploratory in terms of examining which removal mechanism controls P removal. First, wastewater sample data was analyzed to detect significant differences between P concentrations at the beginning of the treatment season compared to the end of treatment season within the WSPs to determine if P is removed over the course of treatment. Then, sediment samples collected from the WSPs were analyzed with a P fractionation method to determine what forms of P are present in the sediment. WSP sediment samples were prepared using two P fractionation methods (Golterman, 1996; Lukkari et al., 2007) to extract different species of P. The data obtained with the method that had the highest percent recovery (Lukkari et al., 2007) was chosen for analysis of fractionation results. Organic-bound P was the largest sediment fraction extracted from both locations, indicating deposition of organic P (partly formed by P assimilation with algae) was one of the dominant P removal mechanisms. The water quality data analysis showed an increase in P in the Pond Inlet WSP, and no change in P concentrations in the Kugaaruk WSP, which may have been due to mobilization of P fractions in the sediment. Over 50% of sediment P extracted at both locations was bound to mobile P fractions, which indicates the mobilization of P from sediment at both locations may have occurred and resulted in increasing P concentrations (Pond Inlet) or no change in P concentrations (Kugarauk) in the water column at both locations. Other parameters examined at both WSPs included: biological oxygen demand (BOD5), total suspended solids (TSS), pH, temperature, and solar radiation. These parameters provided additional measurements of treatment performance and characterization of the WSPs to determine if the removal mechanisms proposed could be supported. The findings of this study identify areas for improvement in treatment performance at both WSP locations, as well as provide a focus for the direction of future research on these types of wastewater treatment systems.