Development of Novel Chitosan–Biochar–Bentonite Composite (CBBC) for Contaminant Barriers

Bentonite is widely used in environmental barrier systems due to its low permeability. However, its limited effectiveness in the removal of a wide range of contaminants reduces its usefulness as a barrier material. While several amendments and modifications have been proposed in the past to enhance bentonite’s adsorption performance, there is a pressing need for sustainable materials in such modifications. The current study investigates the development of a novel chitosan–biochar–bentonite composite (CBBC) barrier to improve the functionality of bentonite in terms of environmental containment. Chitosan, derived from the deacetylation of chitin—a naturally abundant polymer—has been extensively studied for its ability to remove a wide range of contaminants. Biochar, a carbon-rich material made by thermal decomposition of organic matter in the absence of oxygen, is recognized for its adsorption potential due to its large surface area and favorable surface functional groups. Specifically, chitosan derived from crustacean shells and biochar prepared using corn stalk were selected for this study. A novel methodology was developed for synthesizing CBBC from its constituent materials. The CBBC synthesized was tested for its ability to remove nutrients, specifically phosphate and nitrate, from synthetic stormwater. Batch tests were conducted with phosphate and nitrate solutions at varying concentrations (1–8 mg/L for phosphate and 0.5–10 mg/L for nitrate), representing typical concentrations in stormwater runoff. The results showed a significant increase in the phosphate and nitrate adsorption capacity for CBBC (102.04 PO4−3 -P mg/kg and 93.46 NO3−-N mg/kg) compared to bentonite alone (41.49 PO4−3-P mg/kg and 84.03 NO3−-N mg/kg). The adsorption capacities of bentonite and CBBC were modeled using isotherms to understand potential underlying mechanisms. The results of this study offer valuable insights into the effectiveness of CBBC in removing nutrients—highlighting its potential as an efficient barrier in stormwater retention ponds or other waste-containing impoundments.