Influence of Chitosan and Bentonite Characteristics on Phosphate Removal from Stormwater

Containment barrier systems, such as vertical slurry walls and low-permeable liners in waste containment systems, are commonly used to prevent groundwater contamination. However, traditional low-permeable clays used in these barriers have limitations in effectively removing various contaminants, including phosphate, which is a contaminant of global concern. The overarching goal of this work is to create a novel chitosan-bentonite composite barrier for improving the performance of containment systems. Chitosan, a material derived by deacetylating chitin, is a promising barrier material due to its ability to adsorb various contaminants. The purpose of this study is to investigate incorporating chitosan into these barriers to enhance their contaminant adsorption capacity. Previous studies were performed on three chitosans with varying degree of deacetylation (DOD) and molecular weights (MW) and one type of bentonite. The current study presents results from batch tests on four additional chitosan materials and a different source of bentonite. These tests assessed their individual phosphate removal capabilities and were compared with earlier findings. The chitosans exhibited varying phosphate removal efficiencies based on DOD, MW, surface area, and source. The highest removal efficiency ranging from 20.9% to 85.6%, at different initial phosphate concentrations, was achieved by one of the chitosan variants. In contrast, bentonite achieved 15.3% to 41.6% removal at different phosphate concentrations. Results suggest a composite material of chitosan and bentonite in engineered barriers could significantly enhance phosphate removal, especially at lower concentrations (0.5 mg/l), compared to a simple bentonite-based barrier.