Physicochemical characterization of biochar derived from the pyrolysis of cotton gin waste and walnut shells

Authors: NDOUN, MARLENE CARLA - Pennsylvania State University; PREISENDANZ, HEATHER - Pennsylvania State University; Williams, Clinton; Veith, Tameria - Tamie; ELLIOTT, HERSCHEL - Pennsylvania State University; MASHTARE, MICHAEL - Pennsylvania State University; Knopf, Allan; VOZENILEK, NATASHA - Pennsylvania State University; VELEGOL, STEPHANIE - Pennsylvania State University

Submitted to: American Society of Agricultural and Biological Engineers
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/27/2023
Publication Date: 9/1/2023
Citation: Ndoun, M., Preisendanz, H., Williams, C.F., Veith, T.L., Elliott, H.A., Mashtare, M., Knopf, A.L., Vozenilek, N., Velegol, S.B. 2023. Physicochemical characterization of biochar derived from the pyrolysis of cotton gin waste and walnut shells. American Society of Agricultural and Biological Engineers. 66(5): 1163-1174. https://doi.org/10.13031/ja.15489.
DOI: https://doi.org/10.13031/ja.15489

Interpretive Summary: Biochar (a substance similar to charcoal) is produced by burning carbon containing compounds in low oxygen environments. Two agricultural wastes, walnut shells (produced at 800'C, WS800), and cotton gin waste (produced at 700'C, CG700) were prepared. Physical and chemical analysis were used to determine the characteristics of the produced biochar and their potential to be used for pollutant removal from wastewater and soils. Each biochar was characterized by measuring the pH, specific surface area, pore size, particle size, surface charge, and presence of functional groups. The higher temperature used to produce the WS800 led to a higher specific surface area and loss of water from the biochar, as determine by the specific surface area and functional group analysis, respectively. The process of burning the waste to produce the biochar led to the formation of ash which resulted in biochars exhibiting high pH values of 9.85 and 10.93 for the walnut shells and cotton gin waste, respectively. Surface charge measurements demonstrated that both biochars are negatively charged at pH values between 4-10, suggesting suitable applications for the removal of positively charged contaminants from the environment. Overall, results demonstrated that transformation of agricultural waste into biochar leads to the production of value-added materials that possess physical and chemical properties that could prove beneficial for decontamination of wastewater and soil.

Technical Abstract: The sustainable management of agricultural and municipal waste has gained increasing attention worldwide, especially regarding the production and recycling of value-added products that are renewable and carbon-rich. Further, as the beneficial reuse of treated wastewater increases, there is a need to remove contaminants that persist in the effluent to mitigate potential impacts on agroecosystems to which they are land-applied. Here, we characterized biochar produced from the pyrolysis of two agricultural waste products: cotton gin waste (pyrolyzed for 2 h at 700C, CG700) and walnut shells (pyrolyzed for 2 h at 800 C, WS800) to better understand their potential applications for water quality improvement. Each biochar was characterized by Brunauer-Emmett-Teller (BET) analysis to determine the specific surface area, Scanning Electron Microscopy (SEM) to elucidate change in morphology, Fourier Transform Infrared Spectroscopy (FT-IR) to determine surface functional groups, and zeta potential to determine the pH point of zero charge. The higher temperature used to produce WS800 led to an increase in the specific surface area and increased dehydration of the biochar (i.e., loss of the O-H group) as determined by the BET analysis and FT-IR, respectively. Pyrolysis led to destruction of the acidic functional groups and an increase in ash content, resulting in the production of alkaline biochars with pH values of 9.85 and 10.93 for the walnut shells and cotton gin waste, respectively. Zeta potential measurements demonstrated that both biochars are negatively charged at pH values between 4-10, suggesting suitable applications for the removal of cationic contaminants from aqueous systems. Overall, results demonstrated that biochars obtained from agricultural waste have the potential to be effective sorbents for decontamination of wastewater and soil.