Abstract

Different substances are carried from land to water areas such as lakes and ponds by natural or anthropogenic activities. Suspended solids (SS) consisting of organic and inorganic matter are examples of these substances that are discharged into water bodies. Contaminants, such as nutrients, bacteria, and heavy metal, which enter surface waters adsorb onto the surface of these particles and eventually settle on the bottom sediments which then become the largest potential source of contaminants into the overlying water. The presence of these SS in the water causes a decrease in the transparency and also excessive loads of nutrients which lead to eutrophication and rapid growth of algae in the water. Lake Johanne is a shallow mesoeutrophic lake located in the municipality of Saint-Anne-Des-Lacs, Quebec, Canada. The lake was exposed to algal blooms during the hot summer in the past and the water has been found to be turbid since 2008.
The focus of this study was to evaluate the water quality variables of this mesoeutrophic lake, to improve the quality of water using a geotextile filtration technique and thus assess the reliability of the geotextile filters in removing suspended solids and adsorbed nutrients. To accomplish these, lake water quality was monitored for two years (2017-2018). Also, a series of on-site filtration experiments was conducted beside the lake using non-woven geotextiles as filter media. Different combinations of geotextiles, differing in apparent opening sizes and number of layers (5-6), were examined to find the combination showing maximum efficiency in removing SS and associated nutrients. Experiments were classified into four categories with respect to the geotextile combination used as a filter media.
The results obtained from all the experiments conducted with different geotextile combinations were promising for the suspended solids, turbidity, chlorophyll-a, and phosphorus removals. However, combination 3 which included two layers of 100 microns followed by two layers of 90 microns, and two layers of 70 microns showed better results as compared to the other combinations used in this study. The filtration experiments conducted with this combination resulted in 8.3 g /m2-d total suspended solids (TSS), 11.6 mg /m2-d total phosphorus (TP), 9.8 g /m2-d chemical oxygen demand (COD), and 11.1 mg /m2-d chlorophyll-a removal. Overall, the results have indicated the potential of non-woven geotextiles for use as a filter media to improve the quality of surface water by removing SS and algae that impair the water quality. Thus, the geotextile filtration technique can be considered as an effective remediation method for contaminated surface water bodies such as lakes and ponds.