THERMOCHEMICAL PROCESSING OF AGRICULTURAL WASTES TO VALUE-ADDED PRODUCTS AND BIOENERGY
Location: Commodity Utilization Research
Title: Influence of pyrolysis temperature on biochar property and function as heavy metal sorbent in soil
Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 31, 2011
Publication Date: February 24, 2011
Citation: Uchimiya, M., Wartelle, L.H., Klasson, K.T., Fortier, C.A., Lima, I.M. 2011. Influence of pyrolysis temperature on biochar property and function as heavy metal sorbent in soil. Journal of Agricultural and Food Chemistry. 59:2501-2510.
Interpretive Summary: Biochar is one of the products formed during thermochemical waste-to-energy conversion processes. In addition to the use as a fuel, biochar has a wide range of agricultural and environmental applications such as soil fertilization, site remediation, and carbon sequestration. In this study, biochars were produced at different pyrolysis temperatures from cottonseed hulls and were characterized for physical and chemical properties such as the composition and surface area. Characterized biochars were then tested for their ability to sequester heavy metal contaminants when amended in a sandy loam soil. The results suggest that specific measurable properties of biochars, most importantly the surface functional groups, control the ability of biochars to sequester heavy metals in the soil type employed.
While large-scale soil amendment of biochars continues to receive interests for enhancing crop yields and to remediate contaminated sites, systematic study is lacking on how biochar properties translate into purported functions such as the heavy metal sequestration. In this study, cottonseed hulls were pyrolyzed at five temperatures (200, 350, 500, 650, and 800 oC) and characterized for the yield, moisture, ash, volatile matter, and fixed carbon contents, elemental composition (CHNSO), BET surface area, pH, pHpzc, and by ATR-FTIR. The characterization results were compared with literature values for additional source materials: grass, wood, pine needle, and broiler litter-derived biochars with and without post-treatments. At respective pyrolysis temperatures, cottonseed hull chars had ash content in between grass and wood chars, and significantly lower BET surface area in comparison to other plant source materials considered. The N:C ratio reached a maximum between 300 and 400 degrees C for all biomass sources considered, while the following trend in N:C ratio was maintained at each pyrolysis temperature: wood << cottonseed hull ˜ grass ˜ pine needle << broiler litter. To examine how biochar properties translate into its function as heavy metal (NiII, CuII, PbII, and CdII) sorbent, a soil amendment study was conducted for acidic sandy loam Norfolk soil previously shown to have low heavy metal retention capacity. The results suggest that the properties attributable to surface functional groups of biochars (volatile matter and oxygen contents and pHpzc) control the heavy metal sequestration ability in Norfolk soil, and biochar selection for soil amendment must be made case-by-case based on the biochar characteristics, soil property, and the target function.