This study critically appraises employing chitosan as a composite with bentonite, biochar, or both materials as an alternative to conventional barrier materials. A comprehensive literature review was conducted to identify the studies reporting chitosan-bentonite composite (CBC), chitosan amended biochar (CAB), and chitosan-bentonite-biochar composite (CBBC) for effective removal of various contaminants. The study aims to review the synthesis of these composites, identify fundamental properties affecting their adsorption capacities, and examine how these properties affect or enhance the removal abilities of other materials within the composite. Notably, CBC composites have the advantage of adsorbing both cationic and anionic species, such as heavy metals and dyes, due to the cationic nature of chitosan and the anionic nature of montmorillonite, along with the increased accessible surface area due to the clay. CAB composites have the unique advantage of being low-cost sorbents with high specific surface area, affinity for a wide range of contaminants owing to the high surface area and microporosity of biochar, and abundant available functional groups from the chitosan. Limited studies have reported the utilization of CBBC composites to remove various contaminants. These composites can be prepared by combining the steps employed in preparing CBC and CAB composites. They can benefit from the favorable adsorption properties of all three materials while also satisfying the mechanical requirements of a barrier material. This study serves as a knowledge base for future research to develop novel composite barrier materials by incorporating chitosan and biochar as amendments to bentonite.
more »
« less
This content will become publicly available on February 22, 2025
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.
more »
« less
- PAR ID:
- 10528618
- Publisher / Repository:
- American Society of Civil Engineers
- Date Published:
- ISBN:
- 9780784485330
- Page Range / eLocation ID:
- 591 to 601
- Format(s):
- Medium: X
- Location:
- Vancouver, British Columbia, Canada
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Excessive levels of phosphate in stormwater runoff can negatively impact receiving surface water bodies, such as retention ponds, and may also seep into groundwater. Liner systems composed of materials with greater phosphate selectivity have the potential to mitigate infiltration and eliminate phosphate. One potential material is chitosan, an abundant naturally occurring biopolymer. This study evaluated five materials for their ability to remove phosphate from synthetic stormwater using batch tests with different initial phosphate concentrations ranging from 0.5 to 12 mg/L and a fixed 24-h exposure time. The materials included two types of clayey soils (kaolin and bentonite) and three different varieties of chitosan with varying molecular weights (low, medium, and high). The phosphate removal efficiency of kaolin was found to be the highest, with efficiencies ranging from 100% to 56% at different concentrations, while bentonite was found to be the least effective, with removal efficiencies ranging from 40% to 12%. The removal efficiencies of all three types of chitosans analyzed were higher than those of bentonite but lower than those of kaolin. The removal efficiencies ranged from 77% to 19% for low-molecular-weight chitosan, 84% to 31% for medium-molecular-weight chitosan, and 55% to 18% for high-molecular-weight chitosan. The removal mechanism of phosphate by kaolin and bentonite was attributed to surface adsorption and precipitation. In chitosan, the likely mechanism is electrostatic attraction. The maximum adsorption capacity for kaolin was not reached under the tested phosphate concentration range, indicating potential adsorption sites remained available on the particle surfaces. The results for bentonite, low-molecular-weight chitosan, and high-molecular-weight chitosan showed that these materials nearly reached their maximum adsorption capacities, indicating that fewer adsorption sites were remaining. The Langmuir adsorption isotherm was found to be the best-fit model for phosphate adsorption in all the materials tested compared to the Freundlich isotherm. According to the Langmuir model, the maximum adsorption capacities for kaolin, bentonite, low-molecular-weight chitosan, medium-molecular-weight chitosan, and high-molecular-weight chitosan were found to be 140.85, 33, 48.78, 82.64, and 51.28 mg/kg, respectively.more » « less
-
Catastrophic release of heavy metals from the King River mine in Colorado and the Minas Gerais dam in Brazil have brought to the forefront the importance of contaminant stabilization and remediation in surface waters. Permeable reactive materials are currently utilized for the remediation of heavy metals and other pollutants by employing reactive media to remove contaminants. This research investigated the use of fly ashes with loss on ignition or sulfur trioxide exceeding ASTM C618 limits to enhance pollutant removal in pervious concrete. The high carbon and sulfur contents of the noncompliant fly ashes provide additional capacity to remove lead, cadmium, and zinc. High-sulfur and high-carbon fly ashes were less effective in metal removal at higher metal concentrations but improved removal at lower concentrations. These results suggest pervious concrete can be designed as an effective remedial technique for use in many infrastructure applications, including beneath permeable pavement, permeable asphalt, revetment, permeable shoulders, gabions for slope stability, mine tailing dams, and emergency surface water cleanup.more » « less
-
Isotopic analysis of phosphate oxygen from bones and teeth (18Op/16Op, δ18Op) is a common tool used to investigate modern and ancient ecosystems and their climate. However, existing methods have expanded to use pretreatments for organic removal, require large sample sizes, or require extended precipitation timing. All together, these factors could affect accuracy and precision of δ18Op measurement by promoting the formation of oxygen-bearing or nitrogen-rich contaminants. However, the nature and occurrence of contamination are not fully explored. Here we sought to develop a method of silver phosphate precipitation that tests the effect of different sample treatments and reduced sample sizes while preserving sample isotopic composition. Our protocol (SPORA) precipitates Ag3PO4 crystals from ∼1.5 mg of starting material while purifying phosphate from contaminants, like nitrogen or carbonate. Isolation and purification of phosphate are achieved with an anion exchange resin, followed by precipitation of silver phosphate using an updated silver ammine solution that targets small amounts of phosphate in solution. We used a variety of phosphate oxygen reference materials and biogenic apatite materials, such as modern and fossil specimens with varying collagen content, to test the SPORA protocol and its effects on the resultant phosphate oxygen isotopic composition. Results were then compared to those from another published silver phosphate precipitation method (i.e., Rapid University of Chicago Dilute, Rapid UC). Overall, δ18Op values of standards and biogenic apatites were similar between protocols (R2 = 0.99, p << 0.05). In addition to isotope composition comparisons, UV–Vis spectroscopy and Fourier Transform Infrared (FTIR) analyses discerned phosphate recovery and material composition of crystals precipitated via different protocols, respectively. We found that the resin i) may retain ∼10% of phosphate with no isotopic effects and ii) the SPORA protocol produces Ag3PO4 with more accurate δ18Op measurements by preventing the formation of contaminant oxygen phases, silver oxide (Ag2O) and silver carbonate (Ag2CO3), that confound the phosphate oxygen isotope composition. The SPORA Ag3PO4 precipitation procedure overcomes analytical limitations such as sample size and collagen contamination, conditions that other procedures for δ18Op analysis cannot address simultaneously. The SPORA protocol can be used on a large array of bioapatite materials for paleoecological, paleoclimatic, and archeological applications, while reducing the required sample size and ensuring pure Ag3PO4 for isotopic analysis.more » « less
-
Geosynthetic clay liners (GCLs) comprising sodium bentonite (NaB) have been shown to exhibit significant membrane behavior, whereby contaminants are restricted from passing through the clay due to electrostatic repulsion, potentially enhancing long-term containment performance. Recent membrane behavior research has focused on evaluating membrane efficiency () of enhanced bentonites (e.g., bentonite polymer composites) and testing under more complex conditions (e.g., elevated temperatures, unsaturated conditions), often drawing comparisons with earlier published data on NaB-GCLs. However, the validity of comparing NaB-GCL results across studies and from earlier work remains unclear. No prior study has evaluated the variability in reported values for the same type of NaB-GCL manufactured in different years. In this study, multistage membrane behavior tests were performed on specimens of the same NaB-GCL type manufactured at different dates. One specimen (GCL1) was taken from a NaB-GCL roll manufactured in the last five years. Another specimen (GCL2) was taken from a NaB-GCL roll that had been stored in a laboratory since 2005. Values of were measured for both specimens, and also compared to results reported in 2002 for the same type of NaB-GCL (GCL3). To support interpretation of the results, cation exchange capacity, mass per unit area, and swell index tests also were performed. For the same salt solution concentrations, GCL2 exhibited significantly lower than GCL1 and GCL3. Lower values of corresponded to lower bentonite mass per unit area. The results have important implications regarding limitations in comparing results of current membrane behavior research on enhanced materials and testing conditions to commonly cited literature data.more » « less