Fractionation and lability of phosphorus species in cottonseed meal-derived biochars as influenced by pyrolysis temperature

Authors: GUO, MINGXIN - Delaware State University; He, Zhongqi; TIAN, JING - Sichuan University

Submitted to: Molecules
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/3/2024
Publication Date: 1/6/2024
Citation: Guo, M., He, Z., Tian, J. 2024. Fractionation and lability of phosphorus species in cottonseed meal-derived biochars as influenced by pyrolysis temperature. Molecules. 29(2). Article 303. https://doi.org/10.3390/molecules29020303.
DOI: https://doi.org/10.3390/molecules29020303

Interpretive Summary: Worldwide approximately 27.4 million metric tons (121 million bales) of cotton are produced each year, yielding 11.0 million metric tons of lint and 16.4 million metric tons of cottonseed. The residue after oil extraction (defatting) is defatted cottonseed meal (CSM), a brown granular organic solid rich in protein, dietary fiber, and nitrogen, phosphorus and potassium (nutrients. This byproduct is usually utilized as an animal feed or a soil amendment. Converting CSM to biochar and utilizing the goods in agricultural and environmental applications may be a value-added, sustainable approach to recycle the byproduct. This study investigated the chemical transformation of P in CSM during pyrolysis and evaluated the lability of P in CSM-derived biochars generated at varied pyrolysis temperatures, aiming to optimize the pyrolysis operation for converting CSM to biochar products with desirable P supply dynamics in agricultural and environmental applications. This work found that , among the seven biochars prepared at different pyrolysis temperatures, that one made at 600°C exhibited the lowest proportions of readily labile P and residual P, implicating 450°C is the optimal pyrolysis temperature to convert CSM to biochar with maximal P bioavailability and minimal runoff risks.

Technical Abstract: Converting defatted cottonseed meal (CSM) to biochar and utilizing the goods in agricultural and environmental applications may be a value-added, sustainable approach to recycle the byproduct. In this study, raw CSM was transformed into biochar via complete batch slow pyrolysis at 300, 350, 400, 450, 500, 550, and 600°C. Thermochemical transformation of phosphorus (P) in CSM during pyrolysis was explored. Fractionation, lability, and potential bioavailability of total P (TP) in CSM-derived biochars were evaluated using sequential and batch chemical extraction techniques. The recovery of feed P in biochar was nearly 100% at =550°C and reduced to <88% at 600°C. During pyrolysis, the organic P (OP) molecules predominant in CSM was transformed to inorganic P (IP), first to polyphosphates and subsequently to othorphosphates as promoted by higher pyrolysis temperature. Conversion to biochar greatly reduced the mobility, lability, and bioavailability of P in CSM. The biochar TP consisted of 9.3–17.9% of readily labile (water-extractable) P, 10.3–24.1% of generally labile (sequentially NaHCO3-extractable) P, 0.5–2.8% of moderately labile (sequentially NaOH-extractable) P, 17.0–53.8% of low labile (sequentially HCl-extractable) P, and 17.8–47.5% of residual (unextractable) P. Mehlich-3 and 1 M HCl were effective batch extraction reagents for estimating the “readily to mid-term” available and the “overall” available P pools of CSM-derived biochars, respectively. The biochar generated at 450°C exhibited the lowest proportions of readily labile P and residual P compounds, suggesting 450°C as the optimal pyrolysis temperature to convert CSM to biochar with maximal P bioavailability and minimal runoff risks.