Title: Production and characterization of biochars from agricultural by-products for use in soil quality enhancement Authors
|Rehrah, Djaafar -|
|Reddy, Muchha -|
|Bansode, Rishipal -|
|Schimmel, Keith -|
|Yu, Jianmei -|
|Ahmedna, Mohamed -|
Submitted to: Journal of Analytical & Applied Pyrolysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 18, 2014
Publication Date: June 2, 2014
Citation: Rehrah, D., Reddy, M.R., Novak, J.M., Bansode, R., Schimmel, K.A., Yu, J., Watts, D.W., Ahmedna, M. 2014. Production and characterization of biochars from agricultural by-products for use in soil quality enhancement. Journal of Analytical & Applied Pyrolysis. 108:301-304. Interpretive Summary: The production and processing of various agricultural by-products in the form of crop residues such as nutshells, cotton gin, corn cobs, sugarcane bagasse, rice hulls, and straws, etc. into biochar has gained global attention for its use as a soil amendment. Biochar is a solid by-product produced by thermal pyrolysis of these agricultural feedstocks. Because biochars are commonly produced from plants, they will contain a diversity of organic structures and inorganic elements that can serve to increase soil fertility by increasing carbon and plant nutrients. Before biochar is applied to soils, it is useful to chemically and physically characterize the biochar to insure that the integrity of soil health is maintained. We produced biochars from a variety of plant feedstocks at different pyrolysis temperatures to determine the impact of processing conditions on biochar quality. We found that biochar mass recovery and its chemical properties were greatly impacted by produced conditions. For example, more biochar was recovered at lower pyrolysis temperatures (300 degrees Celsius), and had more surface charge. The increase in surface charge implies a higher ability to bind plant nutrients and minimize leaching. In contrast, pyrolysis at higher temperatures (700 degrees Celsius) resulted in biochars with higher surface areas. Biochars with higher surface areas are appropriate for binding organic pollutants. These biochar characteristics are important to determine because it suggests that different biochar types can be produced to selectively improve physicochemical properties of soil through selection of specific feedstocks and pyrolysis conditions.
Technical Abstract: By-products are produced in significant amounts from crop residues such as pecan shells (PC), peanut shells (PS), and cotton gin (CG) trash. These residues can be used to produce biochar suitable for use in agricultural soil to sequester carbon and enhance plant growth by supplying and retaining nutrients while improving soil physical and biological properties. The objectives of this study were to produce biochars from different by-products [PC, PS, CG, and Switchgrass (Panicum virgatum L.)] at different pyrolysis temperatures and times, and to evaluate the resulting biochars physicochemical properties [yield, ash, pH, total surface area (TSA), surface charge (SC), and electrical conductivity (EC)] and elemental composition. Feedstocks were pyrolyzed under nitrogen at 3 temperatures (300, 500, and 750 degrees Celsius) and residence times each (8, 16, and 24 hour), (4, 8, and 12 hour), and (1, 2, and 3 hour), respectively, depending on the nature of the feedstock. Higher pyrolysis temperatures resulted in lower biochar recovery, greater TSA, higher pH, minimal SC, and higher ash contents. Among the eight biochars, switchgrass-derived biochar produced at 750 degree Celsius had the highest TSA followed by PC biochar. Substantial increase in biochar pH (up to 9.8) occurred at the higher temperatures. Biochars produced at lower temperatures (350 degrees Celsius) had measurable SC with PS biochar having the highest value. The highest ash content was observed in CG (up to 34%) compared to other biochars which exhibited <10% ash. These soil-related properties suggest that different biochar types can be produced to selectively improve physicochemical properties of soil through selection of specific feedstocks and pyrolysis conditions.