A Combined Method: Precipitation and Capping, to Attenuate Eutrophication in Canadian Lakes

摘要

Eutrophication is a natural phenomenon, unfortunately amplified and accelerated by human activities. Phosphorus and nitrogen are the principal nutrients responsible for eutrophication. Their excess in the environment, of domestic and agricultural origins, represents an important toxicological risk for the users of water. These excessive nutrients cause algae overgrowth and excess oxygen consumption, which leads to anoxic waters, production of toxins (such as those produced by cyanobacteria), and the production of pollutant gases. Excess nutrients and dead biomass settles at the bottom of the lake together with other trace contaminants such as toxic metals that are trapped within bottom sediments. Seasonally, the sediments release nutrients and contaminants that need to be mitigated in order to prevent eutrophication and overall water contamination. In Quebec and in Canada several lakes suffer from this problem and solutions have been divided in preventive practices (better runoff controls, protection of shores, elimination of leaking domestic septic tanks) and rehabilitating practices (oxygenation of water, precipitation of nutrients, dredging of sediments or capping). This paper will present recent advances in the development of a combined rehabilitating technique: Precipitation of phosphorous and capping of contaminated sediments. The paper includes: a recent literature review; phosphorous precipitation experiments using alum under optimized parameters; capping design considerations and theory; as well as the results of an experimental simulation of capping using a composite liner calcite/sand.