2019 CSCE Annual Conference - Laval (Greater Montreal) Conference
Dr. Catherine Mulligan, Concordia University
Dr. S. Samuel Li, Concordia University
This experimental investigation has been motivated by increasing scenarios of lakes receiving pollutants (heavy metals and nutrients) from various sources. Pollutants can enter the lake and accumulate over time in its sediments. Therefore, there is a need to effectively remove contaminants from the sediments. Field samples of non-uniform sediments from two contaminated lakes in Quebec were obtained and re-suspending of the sediments were examined for removing fine grain sized sediments. In general, the fine grains of contaminated sediment have larger amounts of pollutants adhered to their surfaces because of their higher specific surface area. Removal of these fine grains thus should effectively remove the pollutants. This research focuses on the re-suspension and settling behaviors of non-uniform sediments and the optimization of the removal of fine sediment grains. Laboratory experiments were conducted using a vertical cylinder of 20 cm in diameter and 50 cm in height. During the experiments, sediment samples from the lakes were deposited in tap water at a ratio of 1 gram of dry sediment to 10 ml of water. An air jet of about 10 m/s was injected at the bottom for 2 hours to ensure an even distribution of the sediment grains in the water. Immediately after this action, initial samples of well-mixed sediments and water were taken through an outlet hole in the cylinder wall, located at a height of 10 cm from the bottom. Initial grain sizes distributions were determined using a Laser scattering analyser. During sediment settling, subsequent samples were made every 5 minutes through outlet holes located at heights of 10, 15, 20 and 25 cm, respectively, from the bottom. The turbidity of the samples was measured using a turbidity meter. The sediment concentrations were obtained by measuring the amount of dried sediment on a filter and the volume of extracted water. The preliminary results show that fast settling of coarser gains occurred in the first few minutes. At a given height above the bottom, the grain size, turbidity and sediment concentration decrease with time. At a given time, they decreased with height. Thus in different applications such as phosphorus and heavy metal treatments, by identifying the range of sediments grain sizes which are carrying higher amounts of contaminant, we can target and remove them at the proper settling time and in the suitable height from the bottom which minimizes the amount of sediment removal in the resuspension technique.
Keywords: Sediment resuspension, sediment settling, sediment removal