Water Quality Spatial Heterogeneity in Wastewater Stabilization Ponds at Elevated pH
pH , Algae , Macrophytes , WSP , Wastewater , Lagoon
This thesis consists of work investigating the causes of and solutions to elevated pH in secondary facultative wastewater stabilization ponds (WSPs). Loyalist Township, Ontario, operates a water pollution control plant that employs three facultative WSPs that have experienced elevated pH levels in the summer months due to excessive algae growth. In efforts to comply with a regulated effluent pH of 9.5, the township commissioned this research group at Queen’s University to provide a scientifically proven solution to address this issue. Three studies are presented in this thesis that contribute to interventions that address the elevated pH. The first study examined the feasibility of using WSP sediments already present at the WPCP as a planting substrate for a proposed free water surface constructed wetland. Lab-scale experiments conducted under continuous and batch flow conditions demonstrated that the sediments were able to provide pH attenuation of domestic and synthetic wastewater without causing effluents to exceed regulatory compliance for other water quality parameters. The second study involved a 29-day field scale monitoring program that examined spatial and temporal water quality patterns in the first WSP at the WPCP. Results demonstrated that NO3- and PO43- were removed within the WSP, and that pH, DO, alkalinity, and total NH3 increased within the WSP. It was found that spatial heterogeneity in temperature, pH, and dissolved oxygen exists within the pond, possibly due to the presence of epipelic filamentous algae (Oedogonium) and submerged macrophytes (Myriophyllum, Potamogeton. The third study presented a novel approach to numerically model WSPs that attempted to reproduce the pH, DO, NO3-, total alkalinity, and PO43- observations taken in 2014. The model was the first of its kind to model pH dynamics in a WSP in the presence of filamentous algae and submerged macrophytes. The calibrated model was used to test the effect of increased NH4+ loading, organics loading, the removal of macrophytes, and the removal of the baffle to seasonal effluent pH levels. Increased loading of NH4+ and organics to the system was shown to produce the largest reduction in seasonal pH levels.